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Micromachines
Volume 9
Issue 4
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Micromachines, Volume 9, Issue 4 (April 2018) – 58 articles

Cover Story (view full-size image): Thermotaxis and chemotaxis are defined as the tendency of cells and microorganisms under thermal and chemical gradients to migrate toward favorable physical situations and avoid damage and death. Advances in microfluidics have enhanced the precision of controlling and capturing microscale samples, and bridged the gap between in-vitro and in-situ assays, specifically in taxis experiments. Thermo- and chemotaxis inspired the design and development of novel microfluidic systems and devices based on thermocapillary and chemocapillary flow control. View this paper
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19 pages, 15612 KiB  
Perspective
Emerging Anti-Fouling Methods: Towards Reusability of 3D-Printed Devices for Biomedical Applications
by Eric Lepowsky and Savas Tasoglu
Micromachines 2018, 9(4), 196; https://doi.org/10.3390/mi9040196 - 20 Apr 2018
Cited by 17 | Viewed by 8254
Abstract
Microfluidic devices are used in a myriad of biomedical applications such as cancer screening, drug testing, and point-of-care diagnostics. Three-dimensional (3D) printing offers a low-cost, rapid prototyping, efficient fabrication method, as compared to the costly—in terms of time, labor, and resources—traditional fabrication method [...] Read more.
Microfluidic devices are used in a myriad of biomedical applications such as cancer screening, drug testing, and point-of-care diagnostics. Three-dimensional (3D) printing offers a low-cost, rapid prototyping, efficient fabrication method, as compared to the costly—in terms of time, labor, and resources—traditional fabrication method of soft lithography of poly(dimethylsiloxane) (PDMS). Various 3D printing methods are applicable, including fused deposition modeling, stereolithography, and photopolymer inkjet printing. Additionally, several materials are available that have low-viscosity in their raw form and, after printing and curing, exhibit high material strength, optical transparency, and biocompatibility. These features make 3D-printed microfluidic chips ideal for biomedical applications. However, for developing devices capable of long-term use, fouling—by nonspecific protein absorption and bacterial adhesion due to the intrinsic hydrophobicity of most 3D-printed materials—presents a barrier to reusability. For this reason, there is a growing interest in anti-fouling methods and materials. Traditional and emerging approaches to anti-fouling are presented in regard to their applicability to microfluidic chips, with a particular interest in approaches compatible with 3D-printed chips. Full article
(This article belongs to the Special Issue 3D Printed Microfluidic Devices)
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Figure 1

Figure 1
<p>Schematic representation of 3D printing methods commonly applied in the fabrication of microfluidic devices. (<b>a</b>) Fused deposition modeling (FDM) [<a href="#B48-micromachines-09-00196" class="html-bibr">48</a>]: a solid filament is fed from an external spool through the extrusion head, in which the filament is heated and extruded; (<b>b</b>) Stereolithography (SLA) [<a href="#B49-micromachines-09-00196" class="html-bibr">49</a>]: a laser is directed at a scanning mirror which focuses the laser on a pool of photo-sensitive resin; (<b>c</b>) Photopolymer inkjet printing [<a href="#B50-micromachines-09-00196" class="html-bibr">50</a>]: photopolymer material and support material are fed into an inkjet printing head which deposits the material in layers while an attached UV lamp cures the printed material. Illustrations courtesy of [<a href="#B48-micromachines-09-00196" class="html-bibr">48</a>,<a href="#B49-micromachines-09-00196" class="html-bibr">49</a>,<a href="#B50-micromachines-09-00196" class="html-bibr">50</a>].</p> Full article ">Figure 2
<p>Biomedical applications of 3D-printed microfluidic devices; (<b>a</b>) A combinatorial mixer which generates four titrations of two dye solutions and produces combinatorial mixes of the dye titrations to deliver sixteen mixture combinations into separate outlet microchannels (reproduced, with permission, from [<a href="#B98-micromachines-09-00196" class="html-bibr">98</a>]); (<b>b</b>) a helical-shaped 3D microfluidic device with trapezoidal-shaped channels for the detection of pathogenic bacteria by inertial focusing (reproduced, with permission, from [<a href="#B90-micromachines-09-00196" class="html-bibr">90</a>]); (<b>c</b>) automated 3D-printed microfluidic single-valve device. Below are micrographs of the valve unit in its open and closed states (reproduced, with permission, from [<a href="#B70-micromachines-09-00196" class="html-bibr">70</a>]); (<b>d</b>) single-outlet sub-circuit elements are connected to form a four-outlet mixer. Each sub-circuit element is identical, constituted by a single inlet splitter (reproduced, with permission, from [<a href="#B99-micromachines-09-00196" class="html-bibr">99</a>]); (<b>e</b>) example of a simple, high-throughput mini-bioreactor array (MBRA) used for the cultivation of microbial communities (reproduced, with permission, from [<a href="#B19-micromachines-09-00196" class="html-bibr">19</a>,<a href="#B100-micromachines-09-00196" class="html-bibr">100</a>]); (<b>f</b>) Three-dimensional gradient generator for the mixing of two dyes, consisting of three levels of combining, mixing, and splitting (reprinted, with permission, from [<a href="#B86-micromachines-09-00196" class="html-bibr">86</a>], Copyright 2014 American Chemical Society); (<b>g</b>,<b>h</b>) instrumented cardiac microphysiological device fabricated by multi-material 3D printing; (<b>g</b>) illustration of the working principles of the microphysiological device; (<b>h</b>) images of the fully-printed device (reproduced, with permission, from [<a href="#B101-micromachines-09-00196" class="html-bibr">101</a>]).</p> Full article ">Figure 3
<p>Emerging anti-fouling methods and materials: SLIPS (Slippery Liquid-Infused Porous Surfaces). (<b>a</b>,<b>b</b>) Evolution of the reduction in the visible area of an endoscope surface coated by SLIPS as a function of the number of dips. Silicone oil of low viscosity (10 cSt) was used as the lubricating liquid. Red corresponds to an uncoated endoscope, which fails immediately after a single dip. Green, blue, and black correspond to three replicates of SLIPS coated endoscopes; (<b>a</b>) endoscope dipped in whole porcine blood. Inset images show the visibility of the field of view at 70, 08, and 100 dips for the poorest performing sample; (<b>b</b>) endoscope dipped in mucus. Insets show the visibility of a coated endoscope after repeated dips compared to an untreated endoscope (reproduced, with permission, from [<a href="#B37-micromachines-09-00196" class="html-bibr">37</a>]). (<b>c</b>) Comparison of the repellency of a tethered-liquid perfluorocarbon (TLP) treated surface to an untreated surface (reproduced, with permission, from [<a href="#B35-micromachines-09-00196" class="html-bibr">35</a>]).</p> Full article ">
13 pages, 8738 KiB  
Article
Maskless Surface Modification of Polyurethane Films by an Atmospheric Pressure He/O2 Plasma Microjet for Gelatin Immobilization
by Man Zhang, Yichuan Dai, Li Wen, Hai Wang and Jiaru Chu
Micromachines 2018, 9(4), 195; https://doi.org/10.3390/mi9040195 - 20 Apr 2018
Cited by 8 | Viewed by 5189
Abstract
A localized maskless modification method of polyurethane (PU) films through an atmospheric pressure He/O2 plasma microjet (APPμJ) was proposed. The APPμJ system combines an atmospheric pressure plasma jet (APPJ) with a microfabricated silicon micronozzle with dimension of 30 μm, which has advantages [...] Read more.
A localized maskless modification method of polyurethane (PU) films through an atmospheric pressure He/O2 plasma microjet (APPμJ) was proposed. The APPμJ system combines an atmospheric pressure plasma jet (APPJ) with a microfabricated silicon micronozzle with dimension of 30 μm, which has advantages of simple structure and low cost. The possibility of APPμJ in functionalizing PU films with hydroxyl (–OH) groups and covalent grafting of gelatin for improving its biocompatibility was demonstrated. The morphologies and chemical compositions of the modified surface were analyzed by scanning electronic microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The fluorescent images show the modified surface can be divided into four areas with different fluorescence intensity from the center to the outside domain. The distribution of the rings could be controlled by plasma process parameters, such as the treatment time and the flow rate of O2. When the treatment time is 4 to 5 min with the oxygen percentage of 0.6%, the PU film can be effectively local functionalized with the diameter of 170 μm. In addition, the modification mechanism of PU films by the APPμJ is investigated. The localized polymer modified by APPμJ has potential applications in the field of tissue engineering. Full article
(This article belongs to the Special Issue Plasma-Based Surface Engineering)
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Figure 1
<p>(<b>a</b>) The schematic of the atmospheric pressure plasma microjet (APPμJ) system; (<b>b</b>) photograph of the plasma microjet ejected from a 30 μm silicon micronozzle; (<b>c</b>) local magnified image of the APPμJ.</p> Full article ">Figure 2
<p>(<b>a</b>) Schematic diagram of the inverted pyramid silicon micronozzle fabrication procedure; (<b>b</b>) The diagram of the silicon micronozzle; (<b>c</b>) Scanning electronic microscopy (SEM) images of the silicon micronozzle.</p> Full article ">Figure 3
<p>Schematic diagram of the three-step surface modification protocol.</p> Full article ">Figure 4
<p>Typical current–voltage waveforms of the atmospheric pressure He/O<sub>2</sub> plasma microjet (APPμJ).</p> Full article ">Figure 5
<p>Optical emission spectra of APPμJ under 0.6% O<sub>2</sub>–He gas mixture. (<b>a</b>) Optical emission spectra of the APPμJ under the same applied voltage of ±7.0 kV; (<b>b</b>) Different volumes of oxygen are added to obtain the optimum parameters.</p> Full article ">Figure 6
<p>High-resolution C1s peak of (<b>a</b>) an untreated PU film and (<b>b</b>) a He/O<sub>2</sub> plasma-treated PU film.</p> Full article ">Figure 7
<p>(<b>a</b>) Fluorescence microscope image of the gelatin immobilized PU film which can be divided into four regions (I–IV) depending on the fluorescence intensity; (<b>b</b>) Normalized fluorescent intensity profiles of the dash-dotted line in the fluorescence microscope image; (<b>c</b>) SEM images of plasma treated PU film.</p> Full article ">Figure 8
<p>Raman spectra of the plasma-treated PU film. (<b>a</b>) The Raman spectra of 5 different regions (regions I–IV and the edge region) of the plasma-treated PU film and untreated PU film; (<b>b</b>) Further processed Raman signals of the plasma-treated PU film.</p> Full article ">Figure 9
<p>Fluorescence microscope images of the gelatin immobilized PU films which were treated by plasma microjet with different O<sub>2</sub>/He mixed percentages (0.6–1.0%) for different times (3–6 min). Scale bar: 200 μm.</p> Full article ">
15 pages, 4682 KiB  
Article
Particle-Based Microfluidic Quartz Crystal Microbalance (QCM) Biosensing Utilizing Mass Amplification and Magnetic Bead Convection
by Jan-W. Thies, Bettina Thürmann, Anke Vierheller and Andreas Dietzel
Micromachines 2018, 9(4), 194; https://doi.org/10.3390/mi9040194 - 18 Apr 2018
Cited by 11 | Viewed by 6178
Abstract
Microfluidic quartz crystal microbalances (QCM) can be used as powerful biosensors that not only allow quantifying a target analyte, but also provide kinetic information about the surface processes of binding and release. Nevertheless, their practical use as point-of-care devices is restricted by a [...] Read more.
Microfluidic quartz crystal microbalances (QCM) can be used as powerful biosensors that not only allow quantifying a target analyte, but also provide kinetic information about the surface processes of binding and release. Nevertheless, their practical use as point-of-care devices is restricted by a limit of detection (LoD) of some ng/cm². It prohibits the measurement of small molecules in low concentrations within the initial sample. Here, two concepts based on superparamagnetic particles are presented that allow enhancing the LoD of a QCM. First, a particle-enhanced C-reactive protein (CRP) measurement on a QCM is shown. The signal response could be increased by a factor of up to five by utilizing the particles for mass amplification. Further, a scheme for sample pre-preparation utilizing convective up-concentration involving magnetic bead manipulation is investigated. These experiments are carried out with a glass device that is fabricated by utilizing a femtosecond laser. Operation regimes for the magnetic manipulation of particles within the microfluidic channel with integrated pole pieces that are activated by external permanent magnets are described. Finally, the potential combination of the concepts of mass amplification and up-concentration within an integrated lab-on-a chip device is discussed. Full article
(This article belongs to the Special Issue Microfluidic Sensors)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Flow cell device with integrated microfabricated quartz crystal microbalances (QCM) in comparison to a one-cent coin.</p> Full article ">Figure 2
<p>C-reactive protein (CRP) measurement utilizing the mass enhancement protocol involving a second antibody and streptavidin-coated superparamagnetic nanoparticles.</p> Full article ">Figure 3
<p>(<b>a</b>) Simulation of the magnetic field density within a microfluidic channel surrounded by seven interlocked pole pieces exposed to the field of a one permanent magnet. (<b>b</b>) Progress of the magnetic field density along the blue and red line in <a href="#micromachines-09-00194-f003" class="html-fig">Figure 3</a>a. Colors in both figures indicate their relation. The final magnetic manipulation system is shown in <a href="#sec3dot2-micromachines-09-00194" class="html-sec">Section 3.2</a>.</p> Full article ">Figure 4
<p>Process for fabrication of a magnetic manipulation system made from glass and a stainless steel foil by fs-laser machining (the final device fabricated with this process is shown in <a href="#sec3dot2-micromachines-09-00194" class="html-sec">Section 3.2</a>).</p> Full article ">Figure 5
<p>(<b>a</b>) Pole pieces inlay for the particle manipulation system. (<b>b</b>) Detailed view of three trident pole piece shafts.</p> Full article ">Figure 6
<p>Resonance frequency change for several steps of additional mass up to the complete CRP nanoparticle sandwich. The amount of applied second antibody and nanoparticles is constant for all of the CRP concentrations. Trendlines serve as guide for the eye only.</p> Full article ">Figure 7
<p>The microfluidic bead convection system. (<b>a</b>) The glass channel and pole piece inlays in comparison to a one-cent coin, as well as the assembled device. (<b>b</b>) The system with a cylindrical permanent magnet placed in a three-dimensional (3D) printed holder.</p> Full article ">Figure 8
<p>The retention ration as a function of fluid flow velocities. Typical operational characteristics for the particle convection device equipped with two magnets for varying flow velocities are indicated. The squares represent the oscillating operation mode for the two different magnet pairs. Before reaching the corresponding flow velocities, particles get immobilized near the pole pieces, while for higher flow velocities, the particles leave the system without showing any signs of induced fluctuation.</p> Full article ">Figure 9
<p>Close-up of the fs-laser fabricated pole pieces along the microfluidic channel with immobilized superparamagnetic beads.</p> Full article ">Figure 10
<p>Operation mode concept with achievable unit operations of the magnetic manipulation system in combination with an attached QCM sensor.</p> Full article ">Figure 11
<p>Concept study for the combination of a magnetic manipulation system with fs-laser machined pole pieces and a microfluidic QCM sensor into one lab-on-a-chip system fabricated in glass.</p> Full article ">
10 pages, 3904 KiB  
Article
Parametric Excitation of Optomechanical Resonators by Periodical Modulation
by Jianguo Huang, Muhammad Faeyz Karim, Jiuhui Wu, Tianning Chen and Aiqun Liu
Micromachines 2018, 9(4), 193; https://doi.org/10.3390/mi9040193 - 18 Apr 2018
Cited by 1 | Viewed by 4346
Abstract
Optical excitation of mechanical resonators has long been a research interest, since it has great applications in the physical and engineering field. Previous optomechanical methods rely on the wavelength-dependent, optical anti-damping effects, with the working range limited to the blue-detuning range. In this [...] Read more.
Optical excitation of mechanical resonators has long been a research interest, since it has great applications in the physical and engineering field. Previous optomechanical methods rely on the wavelength-dependent, optical anti-damping effects, with the working range limited to the blue-detuning range. In this study, we experimentally demonstrated the excitation of optomechanical resonators by periodical modulation. The wavelength working range was extended from the blue-detuning to red-detuning range. This demonstration will provide a new way to excite mechanical resonators and benefit practical applications, such as optical mass sensors and gyroscopes with an extended working range. Full article
(This article belongs to the Special Issue Optofluidics: From Fundamental Research to Applications)
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Figure 1

Figure 1
<p>Schematic of different methods for excitation of optomechanical resonators. (<b>a</b>) Passive backaction between cavity and mechanical cantilever by direct current (DC) light using optical anti-damping effect; (<b>b</b>) active feedback control by DC light using optical anti-damping effect; (<b>c</b>) modulated light at twice the mechanical frequency using optical spring effect.</p> Full article ">Figure 2
<p>(<b>a</b>) The schematic illustration of modulated method by alternating current (AC) light using optical spring effect for mechanical excitation; (<b>b</b>) the size of mechanical cantilever.</p> Full article ">Figure 3
<p>The theoretical simulation of the normalized mechanical response under the periodical modulation. (<b>a</b>) The mechanical oscillator is not excited at <span class="html-italic">ε</span> = 0; (<b>b</b>) the mechanical oscillator is excited at <span class="html-italic">ε</span> = 1; (<b>c</b>) the steady amplitudes as a function of the modulation strength.</p> Full article ">Figure 4
<p>(<b>a</b>) scanning electron microscope (SEM) image of the fabricated device; (<b>b</b>) zoom-in view with the width labeled.</p> Full article ">Figure 5
<p>The schematic of the experimental setup. Abbreviations: EOM, electro-optical modulator; CL, optical circulator; VOA, variable optical attenuator; BF, bandpass filter; PD, photon detector; OS, oscilloscope; ASE, amplified spontaneous emission light; OSA, optical spectrum analyzer; S1–S4, optical switch.</p> Full article ">Figure 6
<p>(<b>a</b>) Transmission spectrum of the optical racetrack cavity showing resonance at different optical wavelengths. Resonance wavelength at 1571.86 nm was used as the pump light channel and resonance wavelength at 1587.94 nm was used as the probe light channel. (<b>b</b>) The zoom-in transmission spectrum at 1571.86 nm with a Lorenz fitting, which shows the optical quality factor, is <span class="html-italic">Q</span> = 8.4 × 10<sup>4</sup>.</p> Full article ">Figure 7
<p>(<b>a</b>) The power spectral density of the measured signals, showing the mechanical vibration motions. The inset is the finite element simulation of the two mechanical vibration modes, which correspond to <span class="html-italic">x</span> and <span class="html-italic">z</span> direction. (<b>b</b>) The zoom-in power spectrum density of two mechanical oscillators.</p> Full article ">Figure 8
<p>(<b>a</b>) The power spectral density of the measured signals, showing the thermal mechanical noise (black curve) and amplified mechanical motions (red curve) when the pump light is in the state of off and on separately; (<b>b</b>) the time domain traces showing the original mechanical vibrations and amplified vibrations separately.</p> Full article ">Figure 9
<p>(<b>a</b>) The power spectral density of the measured signals when the wavelength detuning is from −80 pm to 50 pm (curves are vertically offset for clarification); (<b>b</b>) the peak value of power spectral density at the mechanical resonance frequency versus the pump power.</p> Full article ">
11 pages, 3324 KiB  
Article
Multiple Electrohydrodynamic Effects on the Morphology and Running Behavior of Tiny Liquid Metal Motors
by Yue Sun, Shuo Xu, Sicong Tan and Jing Liu
Micromachines 2018, 9(4), 192; https://doi.org/10.3390/mi9040192 - 18 Apr 2018
Cited by 12 | Viewed by 3851
Abstract
Minimized motors can harvest different types of energy and transfer them into kinetic power to carry out complex operations, such as targeted drug delivery, health care, sensing and so on. In recent years, the liquid metal motor is emerging as a very promising [...] Read more.
Minimized motors can harvest different types of energy and transfer them into kinetic power to carry out complex operations, such as targeted drug delivery, health care, sensing and so on. In recent years, the liquid metal motor is emerging as a very promising tiny machine. This work is dedicated to investigate the motion characteristics of self-powered liquid metal droplet machines under external electric field, after engulfing a small amount of aluminum. Two new non-dimensional parameters, named Ä and Ö , are put forward for the first time to evaluate the ratio of the forces resulting from the electric field to the fluidic viscous force and the ratio of the friction force to the fluidic viscous force. Forces exerted on liquid metal droplets, the viscosity between the droplet and the surrounding fluid, the pressure difference on both ends, the friction between the bottom of the droplet and the sink base, and bubble propulsion force are evaluated and estimated regarding whether they are impetus or resistance. Effects of electric field intensity, droplet size, solution concentration and surface roughness etc. on the morphology and running behavior of such tiny liquid metal motors are clarified in detail. This work sheds light on the moving mechanism of the liquid metal droplet in aqueous solutions, preparing for more precise and complicated control of liquid metal soft machines. Full article
(This article belongs to the Special Issue Selected Papers from 2017 International Conference on Micro/Nanomachines)
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Figure 1

Figure 1
<p>Surface charge redistribution of a liquid metal droplet in the electric field.</p> Full article ">Figure 2
<p>Forces analysis diagram for the locomotive liquid metal droplet in the electrical field when (<b>a</b>) the friction force <math display="inline"><semantics> <mrow> <msub> <mi>F</mi> <mi>f</mi> </msub> </mrow> </semantics></math> is an impetus; (<b>b</b>) the friction force <math display="inline"><semantics> <mrow> <msub> <mi>F</mi> <mi>f</mi> </msub> </mrow> </semantics></math> is a resistance.</p> Full article ">Figure 3
<p>Geometrical meaning of parameters in equations.</p> Full article ">Figure 4
<p>The transient velocity of the liquid metal droplet motor under different voltages.</p> Full article ">Figure 5
<p>(<b>a</b>) Movement of the liquid metal droplet on a smooth surface under the impact of different voltages. The displacement and transient velocity change with time of the liquid metal droplet when the applied voltage is (<b>b</b>) 4 V; (<b>c</b>) 16 V; (<b>d</b>) 22 V, respectively, each with a snapshot of the droplet when it is moving at a constant speed.</p> Full article ">Figure 6
<p>The average velocity of the motor varies with droplet sizes.</p> Full article ">Figure 7
<p>The average velocity of the motor varies with solution concentrations.</p> Full article ">Figure 8
<p>(<b>a</b>) Movement of the liquid metal droplet on a rough surface under the impact of different voltages. The displacement and transient velocity change with time of the liquid metal droplet when the applied voltage is (<b>b</b>) 4 V; (<b>c</b>) 16 V; (<b>d</b>) 22 V, respectively, each with a snapshot of the droplet when it is moving at a constant speed.</p> Full article ">Figure 9
<p>The comparison on average velocities of the liquid metal motor between the case of smooth base and the rough base.</p> Full article ">
12 pages, 3483 KiB  
Article
Open Design 3D-Printable Adjustable Micropipette that Meets the ISO Standard for Accuracy
by Martin D. Brennan, Fahad F. Bokhari and David T. Eddington
Micromachines 2018, 9(4), 191; https://doi.org/10.3390/mi9040191 - 18 Apr 2018
Cited by 14 | Viewed by 10241
Abstract
Scientific communities are drawn to the open source model as an increasingly utilitarian method to produce and share work. Initially used as a means to develop freely-available software, open source projects have been applied to hardware including scientific tools. Increasing convenience of 3D [...] Read more.
Scientific communities are drawn to the open source model as an increasingly utilitarian method to produce and share work. Initially used as a means to develop freely-available software, open source projects have been applied to hardware including scientific tools. Increasing convenience of 3D printing has fueled the proliferation of open labware projects aiming to develop and share designs for scientific tools that can be produced in-house as inexpensive alternatives to commercial products. We present our design of a micropipette that is assembled from 3D-printable parts and some hardware that works by actuating a disposable syringe to a user-adjustable limit. Graduations on the syringe are used to accurately adjust the set point to the desired volume. Our open design printed micropipette is assessed in comparison with a commercial pipette and meets the ISO 8655 standards. Full article
(This article belongs to the Special Issue 3D Printed Microfluidic Devices)
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Figure 1

Figure 1
<p>CAD renderings of printable parts and cross-sections. (<b>A</b>) The printed plunger part is a shaft that pushes on the syringe plunger and slides in the printed body part. The printed plunger has a latching tongue and button, which interfaces with the printed body part. (<b>B</b>) The printed body part holds the syringe and interfaces with the printed plunger part. The body part features the unlatching button and slots to hold the syringe in place by its flanges. The body part also has two cutouts in the top for the plunger button and for the hex nut and bolt. STL files of the printable parts are available in the <a href="#app1-micromachines-09-00191" class="html-app">Supplementary Materials</a>.</p> Full article ">Figure 2
<p>CAD renderings of assembled pipette and function. The pipette actuates the syringe to three positions. (<b>A</b>) The latched position. When the plunger is pressed, the pipette locks at this position. The tip is then placed in a liquid, and the unlatching button is pressed to release the pipette back to the set position (<b>B</b>), drawing in liquid. (<b>B</b>) The set position. The position of the screw determines the total displacement that the plunger moves. The pipette is spring loaded to return to this position. (<b>C</b>) The blow-out position. The fluid is transferred by pressing the plunger past the latched position to blow-out all the liquid. (<b>D</b>) Return to the latched position. The pipette returns to the latched position ready to perform another transfer.</p> Full article ">Figure 3
<p>Photo of the parts to make the pipette. (<b>A</b>) Printed body part. (<b>B</b>) Printed plunger part. (<b>C</b>) Springs. (<b>D</b>) M3 hex nut and M3 bolt. (<b>E</b>) Disposable syringes. (<b>F</b>) Two sizes of tubing to adapt pipette tips to luer barbs. (<b>G</b>) Luer lock syringe-to-barb adapters. (<b>H</b>) Pipette tips. A list of parts is in <a href="#app2-micromachines-09-00191" class="html-app">Appendix A</a>: <a href="#micromachines-09-00191-t0A1" class="html-table">Table A1</a> and <a href="#micromachines-09-00191-t0A2" class="html-table">Table A2</a>.</p> Full article ">Figure 4
<p>Photos of assembled pipettes. (<b>A</b>) Two assemblies of the pipette: the 100–1000-<math display="inline"> <semantics> <mi mathvariant="sans-serif">μ</mi> </semantics> </math>L configuration (top) and the 30–300-<math display="inline"> <semantics> <mi mathvariant="sans-serif">μ</mi> </semantics> </math>L configuration (bottom). (<b>B</b>) Close-up photo of the taped on scale for each of the syringes. Scales are available in the <a href="#app2-micromachines-09-00191" class="html-app">Appendix A</a>: <a href="#micromachines-09-00191-f0A1" class="html-fig">Figure A1</a> and <a href="#micromachines-09-00191-f0A2" class="html-fig">Figure A2</a>.</p> Full article ">Figure 5
<p>Comparison of the accuracy, or systematic error, among 100–1000-<math display="inline"> <semantics> <mi mathvariant="sans-serif">μ</mi> </semantics> </math>L pipettes. The box plot indicates the range of the ISO standard; the plotted circle indicates the commercial pipette; and the plotted squares are the printed pipette. Empty squares are with the printed pipette with our adjusted graduation scale, and the filled squares are measurements taken with the syringe’s existing graduations (data from <a href="#micromachines-09-00191-t001" class="html-table">Table 1</a>.)</p> Full article ">Figure 6
<p>Comparison of the accuracy, or systematic error, among 30–300-<math display="inline"> <semantics> <mi mathvariant="sans-serif">μ</mi> </semantics> </math>L pipettes. The box plot indicates the range of the ISO standard; the plotted circle indicates the commercial pipette; and the plotted squares are the printed pipette. Empty squares are with the printed pipette with our adjusted graduation scale, and the filled squares are measurements taken with the syringe’s existing graduations (data from <a href="#micromachines-09-00191-t002" class="html-table">Table 2</a>.)</p> Full article ">Figure A1
<p>Adjusted scale graduations for the 30–300-<math display="inline"> <semantics> <mi mathvariant="sans-serif">μ</mi> </semantics> </math>L pipette. Adjusted scale graduations that can be printed on paper or a transparency sheet and taped onto a 1-mL syringe. Using these graduations will correct for expansion of air and allow ISO standards to be met. One-inch and 1-cm marks to check the scale are included, as well as a reproduction of the existing 1-mL syringe graduation marks.</p> Full article ">Figure A2
<p>Adjusted scale graduations for the 100–1000-<math display="inline"> <semantics> <mi mathvariant="sans-serif">μ</mi> </semantics> </math>L pipette. Adjusted scale graduations that can be printed on paper or a transparency sheet and taped onto a 3-mL syringe. Using these graduations will correct for expansion of air and allow ISO standards to be met. One-inch and 1-cm marks to check the scale are included, as well as a reproduction of the existing 3-mL syringe graduation marks. Print this image to 100% scale.</p> Full article ">
15 pages, 31184 KiB  
Article
Electrostatically Driven In-Plane Silicon Micropump for Modular Configuration
by Sebastian Uhlig, Matthieu Gaudet, Sergiu Langa, Klaus Schimmanz, Holger Conrad, Bert Kaiser and Harald Schenk
Micromachines 2018, 9(4), 190; https://doi.org/10.3390/mi9040190 - 18 Apr 2018
Cited by 39 | Viewed by 5064
Abstract
In this paper, an in-plane reciprocating displacement micropump for liquids and gases which is actuated by a new class of electrostatic bending actuators is reported. The so-called “Nano Electrostatic Drive” is capable of deflecting beyond the electrode gap distance, enabling large generated forces [...] Read more.
In this paper, an in-plane reciprocating displacement micropump for liquids and gases which is actuated by a new class of electrostatic bending actuators is reported. The so-called “Nano Electrostatic Drive” is capable of deflecting beyond the electrode gap distance, enabling large generated forces and deflections. Depending on the requirements of the targeted system, the micropump can be modularly designed to meet the specified differential pressures and flow rates by a serial and parallel arrangement of equally working pumping base units. Two selected, medium specific micropump test structure devices for pumping air and isopropanol were designed and investigated. An analytical approach of the driving unit is presented and two-way Fluid-Structure Interaction (FSI) simulations of the micropump were carried out to determine the dynamic behavior. The simulation showed that the test structure device designed for air expected to overcome a total differential pressure of 130 kPa and deliver a flow rate of 0.11 sccm at a 265 Hz driving frequency. The isopropanol design is expected to generate 210 kPa and pump 0.01 sccm at 21 Hz. The device is monolithically fabricated by CMOS-compatible bulk micromachining processes under the use of standard materials only, such as crystalline silicon, silicon dioxide and alumina. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International Conference on Microfluidic Handling Systems)
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<p>Representation of clamped-free NED actuator with length <span class="html-italic">L</span>. Radius of curvature defined positive, as shown. (<b>a</b>) Non-actuated state; (<b>b</b>) actuated state—cylindrical bending line.</p> Full article ">Figure 2
<p>Sketch of four specifically arranged NED actuator beams and their bending line in (c-c) configuration, when actuated.</p> Full article ">Figure 3
<p>Sketch of the pumping principle based on a NED actuator beam in (c-c) configuration in combination with 3 passive check valves: (<b>a</b>) Active displacement associated to a pump stroke; (<b>b</b>) Passive displacement associated to an intake stroke. Flow and actuator movement direction indicated by arrows.</p> Full article ">Figure 4
<p>Pressure/displacement graph and concept of NED actuation scheme in the micropump.</p> Full article ">Figure 5
<p>Base pumping unit of NED micropump (dashed rectangle marks off imaginary unit boarder). (<b>a</b>) Active stroke, transfer of fluid via valves on right-hand side; (<b>b</b>) Passive stroke, transfer of fluid via left-hand sided valves. Arrows indicate direction of flow.</p> Full article ">Figure 6
<p>Micrograph of the device layer of the complete in-plane test structure chip dedicated to pumping IPA. The dashed rectangle indicates one base pumping unit within one pump block, while the dash-dotted rectangle indicated the pump block itself.</p> Full article ">Figure 7
<p>Micrographs of fabricated NED micropump test samples. (<b>a</b>) DRIE test etching of electrostatic gap (BOX-layer not released). Inset shows encapsulation of the NED electrodes by 60 nm ALD-Al<sub>2</sub>O<sub>3</sub>; (<b>b</b>) Device layer of micropump test sample designed for IPA. Inset shows passive flap valves and beginning of defined shaped NED electrodes.</p> Full article ">Figure 8
<p>Sketch of a cross-section through the micropump test structure chip shows the sandwich of the three-layer silicon wafer stack. The NED actuators of one base unit moving in plane (indicated). The fluidic leak through clearance above and below the actuators is shown as well.</p> Full article ">Figure 9
<p>Sketch (2D) of the model setup used for the 2-way FSI simulation of the behavior of one base unit.</p> Full article ">Figure 10
<p>Ramped step function of NED actuator beam effective moments in “ANSYS mechanical”. The values are scaled to a 2.5D model slice height of 4 µm.</p> Full article ">Figure 11
<p>Results of the transient FSI simulation. (<b>a</b>) Maximum deflection of actuators and valves; (<b>b</b>) Differential pressure behavior; (<b>c</b>) One-phase flow rate through the cavity extrapolated to 75 µm of the device layer height.</p> Full article ">Figure 12
<p>Generated differential pressure vs. displacement graph, obtained from the simulation results as well as analytical model. The resulting stroke volume for corresponding displacements of the NED actuator beams in (c-c) configuration is written on the top <span class="html-italic">x</span> axis. The intended operation point of the micropump is at the half of the actuator displacement.</p> Full article ">Figure 13
<p>Frequency-dependent output flow rate behavior for (<b>a</b>) Base unit Design A (air); (<b>b</b>) Base unit Design B (IPA). The dashed curves (left <span class="html-italic">y</span> axis) display the corresponding actuation zone widths. (Dotted) Linear Extrapolation to zero flow rates due to simulation end time.</p> Full article ">Figure A1
<p>Results of the spatial discretization refinement analysis of the structural and fluid domain mesh (grid). The chosen mesh densities used in the simulation are indicated in red.</p> Full article ">
18 pages, 38516 KiB  
Article
Position-Space-Based Design of a Symmetric Spatial Translational Compliant Mechanism for Micro-/Nano-Manipulation
by Haiyang Li and Guangbo Hao
Micromachines 2018, 9(4), 189; https://doi.org/10.3390/mi9040189 - 17 Apr 2018
Cited by 22 | Viewed by 5324
Abstract
Symmetry enables excellent motion performance of compliant mechanisms, such as minimized parasitic motion, reduced cross-axis coupling, mitigated buckling, and decreased thermal sensitivity. However, most existing symmetric compliant mechanisms are heavily over-constrained due to the fact that they are usually obtained by directly adding [...] Read more.
Symmetry enables excellent motion performance of compliant mechanisms, such as minimized parasitic motion, reduced cross-axis coupling, mitigated buckling, and decreased thermal sensitivity. However, most existing symmetric compliant mechanisms are heavily over-constrained due to the fact that they are usually obtained by directly adding over-constraints to the associated non-symmetric compliant mechanisms. Therefore, existing symmetric compliant mechanisms usually have relatively complex structures and relatively large actuation stiffness. This paper presents a position-space-based approach to the design of symmetric compliant mechanisms. Using this position-space-based approach, a non-symmetric compliant mechanism can be reconfigured into a symmetric compliant mechanism by rearranging the compliant modules and adding minimal over-constraints. A symmetric spatial translational compliant parallel mechanism (symmetric XYZ compliant parallel mechanism (CPM)) is designed using the position-space-based design approach in this paper. Furthermore, the actuation forces of the symmetric XYZ CPM are nonlinearly and analytically modelled, which are represented by the given primary translations and the geometrical parameters. The maximum difference, between the nonlinear analytical results and the nonlinear finite element analysis (FEA) results, is less than 2.58%. Additionally, a physical prototype of the symmetric XYZ CPM is fabricated, and the desirable motion characteristics such as minimized cross-axis coupling are also verified by FEA simulations and experimental testing. Full article
(This article belongs to the Section A：Physics)
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<p>Position-space-based reconfiguration of a general one degree of freedom (1-DOF) translational compliant mechanism: (<b>a</b>) original 1-DOF translational compliant mechanism; (<b>b</b>) decomposition of the 1-DOF translational compliant mechanism; (<b>c</b>) change of geometrical dimension; (<b>d</b>) change of geometrical shape; (<b>e</b>) changes of both geometrical dimension and geometrical shape; and (<b>f</b>) addition of redundant compliant modules (MS: motion stage, BS: base stage, RL: rigid link, compliant modules are labelled by numbers (1) to (5)).</p> Full article ">Figure 2
<p>Position-space-based reconfiguration for generating a 1-DOF symmetric translational compliant mechanism: (<b>a</b>) decomposition of the 1-DOF translational compliant mechanism; (<b>b</b>) translations of compliant modules; (<b>c</b>) rotations of compliant modules; (<b>d</b>) further translations of compliant modules; (<b>e</b>) symmetric 1-DOF translational compliant mechanism; and (<b>f</b>) deformation of the 1-DOF translational compliant mechanism under an actuation force.</p> Full article ">Figure 3
<p>A symmetric XYZ compliant parallel mechanism (CPM) obtained via reconfiguring a non-symmetric XYZ CPM: (<b>a</b>) the original non-symmetric XYZ CPM [<a href="#B29-micromachines-09-00189" class="html-bibr">29</a>]; (<b>b</b>) decomposition of the non-symmetric XYZ CPM; (<b>c</b>) further decomposition of the actuated compliant modules (AMs) of the non-symmetric XYZ CPM; (<b>d</b>) AM-X-1 translated to a new permitted position; (<b>e</b>) addition of redundant compliant modules (over-constraints); (<b>f</b>) reconfiguration of the legs associated with the translations along the Y<sub>ms</sub>- and Z<sub>ms</sub>-axes; (<b>g</b>) BS design; (<b>h</b>) resulting symmetric XYZ CPM; and (<b>i</b>) symmetric XYZ CPM designed by traditional approach, i.e., directly adding redundant compliant modules.</p> Full article ">Figure 4
<p>Compliant modules: (<b>a</b>) A two-beam compliant module (TBCM) and its coordinate system and (<b>b</b>) a four-beam compliant module and its coordinate system.</p> Full article ">Figure 5
<p>Simplified spring model of the symmetric XYZ CPM with illustrative force actuation along the X-axis (RL-X is red in color, RL-Y is green in color, and RL-Z is blue in color).</p> Full article ">Figure 6
<p>Comparison between the analytical results and the finite element analysis (FEA) results in terms of the force-displacement relationship.</p> Full article ">Figure 7
<p>Variation of actuation force, <span class="html-italic">f</span><sub>x</sub>, with <span class="html-italic">ξ</span><sub>asy</sub> and <span class="html-italic">ξ</span><sub>asz</sub>, when <span class="html-italic">ξ</span><sub>asx</sub> = 0.</p> Full article ">Figure 8
<p>Comparison of lost motions between the symmetric and non-symmetric XYZ CPMs shown in <a href="#micromachines-09-00189-f003" class="html-fig">Figure 3</a>a,h (Symbols, ‘*’, ‘△’ and ‘○’, in this figure are data points).</p> Full article ">Figure 9
<p>Comparison of input parasitic translations between the symmetric and non-symmetric XYZ CPMs shown in <a href="#micromachines-09-00189-f003" class="html-fig">Figure 3</a>a,h (Symbols, ‘*’, ‘△’ and ‘○’, in this figure are data points).</p> Full article ">Figure 10
<p>Comparison of input parasitic rotations between the symmetric and non-symmetric XYZ CPMs shown in <a href="#micromachines-09-00189-f003" class="html-fig">Figure 3</a>a,h (Symbols, ‘*’, ‘△’ and ‘○’, in this figure are data points).</p> Full article ">Figure 11
<p>Comparison of output parasitic rotations between the symmetric and non-symmetric XYZ CPMs shown in <a href="#micromachines-09-00189-f003" class="html-fig">Figure 3</a>a,h (Symbols, ‘*’, ‘△’ and ‘○’, in this figure are data points).</p> Full article ">Figure 12
<p>Coupling comparison between the symmetric and non-symmetric XYZ CPMs shown in <a href="#micromachines-09-00189-f003" class="html-fig">Figure 3</a>a,h (Symbols, ‘*’, ‘△’ and ‘○’, in this figure are data points).</p> Full article ">Figure 13
<p>Main assembling components: (<b>a</b>) rigid cube; (<b>b</b>) rigid washer; (<b>c</b>) compliant passive compliant modules (PM) beam; and (<b>d</b>) compliant AM beam.</p> Full article ">Figure 14
<p>Assembling demonstration of the practical design: (<b>a</b>–<b>e</b>) assembling of rigid cubes, rigid washers, compliant PM beams, and compliant AM beams; (<b>f</b>) assembling of three RLs; (<b>g</b>) assembling of output platform; and (<b>h</b>) assembling of supporting seat.</p> Full article ">Figure 15
<p>A prototype of the practical design.</p> Full article ">Figure 16
<p>Relationship between the input displacement and the output displacement along the X<sub>ms</sub>-axis.</p> Full article ">
12 pages, 5116 KiB  
Article
A Horizontal Magnetic Tweezers and Its Use for Studying Single DNA Molecules
by Roberto Fabian, Jr., Christopher Tyson, Pamela L. Tuma, Ian Pegg and Abhijit Sarkar
Micromachines 2018, 9(4), 188; https://doi.org/10.3390/mi9040188 - 17 Apr 2018
Cited by 12 | Viewed by 5733
Abstract
We report the development of a magnetic tweezers that can be used to micromanipulate single DNA molecules by applying picoNewton (pN)-scale forces in the horizontal plane. The resulting force–extension data from our experiments show high-resolution detection of changes in the DNA tether’s extension: [...] Read more.
We report the development of a magnetic tweezers that can be used to micromanipulate single DNA molecules by applying picoNewton (pN)-scale forces in the horizontal plane. The resulting force–extension data from our experiments show high-resolution detection of changes in the DNA tether’s extension: ~0.5 pN in the force and <10 nm change in extension. We calibrate our instrument using multiple orthogonal techniques including the well-characterized DNA overstretching transition. We also quantify the repeatability of force and extension measurements, and present data on the behavior of the overstretching transition under varying salt conditions. The design and experimental protocols are described in detail, which should enable straightforward reproduction of the tweezers. Full article
(This article belongs to the Special Issue Micro Technologies for Single Molecule Manipulation and Detection)
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<p>Basic principle of the horizontal magnetic tweezers: (<b>a</b>) the tweezers uses a rigid functionalized glass pipette to manipulate a bead attached to one end of a DNA tether and immobilized by biotin-streptavidin interactions to the surface of a rigid glass pipette. The other end of the tether is attached to a superparamagnetic bead suspended in buffer and placed at varying distances from a 3 mm × 2 mm × 1 mm bar magnet. Forces ranging from 0.5 pN to 100 pN (and higher) can be produced by moving the DNA-magnet distance from 2000 μm to 100 μm; (<b>b</b>) the design of the sample cell is shown. The sample cell has an inlet and an outlet for buffer exchange. The open side of the sample cell allows the insertion of the functionalized glass pipette used to capture and immobilize DNA-bead pairs; (<b>c</b>) a block diagram showing the layout of the horizontal magnetic tweezers.</p> Full article ">Figure 2
<p>Experimental results of force vs DNA extension experiments on λ-DNA using the horizontal magnetic tweezers. Our data are represented by the solid black circles; corresponding standard errors in the forces are shown by blue lines. The solid red line represents the worm-like chain model for a single DNA molecule’s response to force, which agrees well with our data in the 1.0 pN to 40 pN force range. This corresponds to DNA extension from 13.7 μm to 16.2 μm. Between 40 pN to 60 pN our data begins to deviate to the right from the worm-like chain model. This is the region where the DNA is at is full contour length (around 25 pN) and then begins to stretch. At force range of 52.8 pN up to 60.1 pN with corresponding DNA extension of 16.5 μm up to 16.8 μm, our data further shifted to the right from the worm-like chain model. At force range of 64.7 pN up to 73.7 pN with corresponding DNA extension of 18.2 μm up to 29.3 μm, the DNA tether undergoes the overstretching transition with its zero-force contour length <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mi>o</mi> </msub> </mrow> </semantics></math> increasing by 70% of <math display="inline"><semantics> <mrow> <msub> <mi>L</mi> <mi>o</mi> </msub> </mrow> </semantics></math>. The inset shows two snapshots from our DNA extension experiments. From left to right, the first snapshot shows a single DNA with contour length of 16.4 μm with the tethered bead 550 μm from the magnet and corresponding to a force of 44.2 pN. The second snapshot shows a single DNA molecule in the overstretching transition with an extension of 28.5 μm, ~<math display="inline"><semantics> <mrow> <mn>1.7</mn> <msub> <mi>L</mi> <mi>o</mi> </msub> </mrow> </semantics></math>, at 430 μm from the magnet for a force of ~66.8 pN.</p> Full article ">Figure 3
<p>Magnetic force acting on a 2.8 μm superparamagnetic bead as a function of distance from the magnet. The solid black circles represent the force at each position from the magnet—see <a href="#micromachines-09-00188-t001" class="html-table">Table 1</a> columns 1 and 2. The blue lines represent the standard error in the forces—see <a href="#micromachines-09-00188-t001" class="html-table">Table 1</a> column 3.</p> Full article ">Figure 4
<p>Replications of force–extension measurements using five different magnets and comparison to calibration data. The WLC is plotted as red solid line. The black solid circles represent the experimental results on λ-DNA using optical tweezers as presented in Strick et al. [<a href="#B11-micromachines-09-00188" class="html-bibr">11</a>]. The remaining solid colored circles represent data from our experimental replications.</p> Full article ">Figure 5
<p>Hysteresis in DNA overstretching transition: (<b>a</b>) the extension-time graph of the DNA during a reversible overstretching transition. This experiment is done on 1× Tris-EDTA (TE) buffer with 150 mM NaCl at room temperature. Looking left to right, the extensional and contractile phases are symmetrical; (<b>b</b>) the extension-time graph of the DNA during a hysteretic overstretching transition. This experiment is done on 1× TE buffer in the absence of salt at room temperature. Looking left to right, the asymmetry between the extensional and contractile responses is clear visible. Bead-magnet distance are adjusted at a speed of 10 μm/s in (<b>a</b>,<b>b</b>).</p> Full article ">
13 pages, 33679 KiB  
Article
Progress on the Use of Commercial Digital Optical Disc Units for Low-Power Laser Micromachining in Biomedical Applications
by Aarón Cruz-Ramírez, Raúl Sánchez-Olvera, Diego Zamarrón-Hernández, Mathieu Hautefeuille, Lucia Cabriales, Edgar Jiménez-Díaz, Beatriz Díaz-Bello, Jehú López-Aparicio, Daniel Pérez-Calixto, Mariel Cano-Jorge and Genaro Vázquez-Victorio
Micromachines 2018, 9(4), 187; https://doi.org/10.3390/mi9040187 - 16 Apr 2018
Cited by 7 | Viewed by 6184
Abstract
The development of organ-on-chip and biological scaffolds is currently requiring simpler methods for microstructure biocompatible materials in three dimensions, to fabricate structural and functional elements in biomaterials, or modify the physicochemical properties of desired substrates. Aiming at addressing this need, a low-power CD-DVD-Blu-ray [...] Read more.
The development of organ-on-chip and biological scaffolds is currently requiring simpler methods for microstructure biocompatible materials in three dimensions, to fabricate structural and functional elements in biomaterials, or modify the physicochemical properties of desired substrates. Aiming at addressing this need, a low-power CD-DVD-Blu-ray laser pickup head was mounted on a programmable three-axis micro-displacement system in order to modify the surface of polymeric materials in a local fashion. Thanks to a specially-designed method using a strongly absorbing additive coating the materials of interest, it has been possible to establish and precisely control processes useful in microtechnology for biomedical applications. The system was upgraded with Blu-ray laser for additive manufacturing and ablation on a single platform. In this work, we present the application of these fabrication techniques to the development of biomimetic cellular culture platforms thanks to the simple integration of several features typically achieved with traditional, less cost-effective microtechnology methods in one step or through replica-molding. Our straightforward approach indeed enables great control of local laser microablation or polymerization for true on-demand biomimetic micropatterned designs in transparent polymers and hydrogels and is allowing integration of microfluidics, microelectronics, surface microstructuring, and transfer of superficial protein micropatterns on a variety of biocompatible materials. Full article
(This article belongs to the Special Issue Micro-Machining: Challenges and Opportunities)
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Full article ">Figure 1
<p>Diagrams of the laser ablation (<b>a</b>) and DLW (<b>b</b>) microfabrication methods to fabricate microstructures directly in transparent plastics such as PMMA, PDMS, PLA, and Loctite 3525 (<b>c1</b>) or by direct laser writing in Loctite 3525 (<b>c2</b>). Everything was achieved with the benchtop laser platform with two laser wavelengths (<b>d</b>). Electronics are not shown for clarity. Scale bars are 1 mm.</p> Full article ">Figure 2
<p>Laser-etching control in PMMA substrates: average depth (<b>a</b>) and width (<b>b</b>) as a function of laser power density and pulse time. Data points are averaged over the full patterns.</p> Full article ">Figure 3
<p>Example of a 3D profile obtained by ablation with multiple laser passes: (<b>a</b>) 3D profile of the successive etched layers; (<b>b</b>) the average depth of a square region etched one to five times (1X to 5X); and (<b>c</b>) the Root Mean Square roughness of the etched area as a function of the number of passes.</p> Full article ">Figure 4
<p>(<b>a1</b>) Dimensions of crosslinked features on Loctite 3525, and profiles of the (<b>a2</b>) smallest and (<b>a3</b>) tallest features fabricated with 4 W/cm<sup>2</sup> and 106 W/cm<sup>2</sup> respectively. (<b>b1</b>) SEM micrograph of a 3D pyramid fabricated on a single layer of Loctite 3525 by crosslinking the material in a Z-stepper fashion with a laser power density of 37.05 W/cm<sup>2</sup>; and (<b>b2</b>) the profile measured at the middle of the pyramid.</p> Full article ">Figure 5
<p>Microelectrodes fabrication processes: local laser ablation of PMMA etches interdigitated microchannels that are filled with carbon paste using doctor blading (<b>a1</b>–<b>a4</b>) and DLW is used on a thin Loctite layer as a protective coating to chemically etch a PCB copper board (<b>b1</b>–<b>b5</b>) Scale bars are 500 µm and 1 mm for (<b>a4</b>) and (<b>b5</b>) respectively.</p> Full article ">Figure 6
<p>(<b>a</b>) Laser micropatterned PMMA mold for two-input two-output microfluidic channel design. (<b>b</b>) Example of colorant diffusion microfluidics inside PDMS microchannel for bonding validation. (<b>c</b>) Microfluidic device (Scale bars: (<b>a</b>) 1 mm, (<b>b</b>) 500 µm, (<b>c</b>) 5 mm).</p> Full article ">Figure 7
<p>(<b>a</b>) Bright field photograph of a squared microwell. (<b>b</b>) Regionalized hepatic C9 cells cultured onto PDMS replica, (yellow discontinued square corresponds to (<b>c</b>) and the red one corresponds to (<b>d</b>)). (<b>c</b>) In response to spatial confinement, cells upon/atop the microwell present YAP/TAZ (green) in the cytoplasm as shown by the non-colocalization with the nuclei stained with DAPI (blue). (<b>d</b>) On the contrary, cells outside the microwell, have YAP/TAZ in the nuclei, as shown by the colocalization with DAPI (full experiment unpublished at the time).</p> Full article ">Figure 8
<p>Diagram of PMMA laser etching for the fabrication of µCP master molds: (<b>a1</b>) Laser etching of PMMA to obtain a mastermold, (<b>a2</b>) PDMS is poured onto the PMMA structured master, (<b>a3</b>) the stamp is peeled off the master, (<b>a4</b>) the stamp is incubated with an ink solution, (<b>a5</b>) the excess of solution is removed, (<b>a6</b>) the inked stamp is placed onto a glass coverslip and the protein pattern is suitable for cell culture. (<b>b</b>) HepG2 cells grow selectively onto the collagen I protein pattern (green is calcein (live cells), scale bar: 100 µm. Diagram of Loctite DLW for the fabrication of µCP stamps in one single step: (<b>c1</b>) Selective laser crosslinking of Loctite to obtain the desired stamp, (<b>c2</b>) the stamp is incubated with an ink solution, (<b>c3</b>) the excess of the solution is removed, (<b>c4</b>) the inked stamp is placed onto a glass coverslip and the protein pattern is suitable for cell culture. (<b>d</b>) HepG2 cells onto the transferred protein pattern (green is phalloidin as actin cytoskeleton marker), scale bar: 100 µm.</p> Full article ">Figure 9
<p>Polyacrylamide hydrogels with microposts structures: PMMA laser-etched mold with microwells (<b>a</b>), vertical microposts are transferred to polyacrylamide (<b>b</b>) and A549 cells were seeded on 300 micron wide hydrogel pillars for confinement studies (<b>c</b>). Scale bars are 3 mm for (<b>a</b>), 1 cm for (<b>b</b>), and 100 µm for (<b>c</b>).</p> Full article ">
11 pages, 18123 KiB  
Article
Fabrication of an Anti-Reflective and Super-Hydrophobic Structure by Vacuum Ultraviolet Light-Assisted Bonding and Nanoscale Pattern Transfer
by Yuki Hashimoto and Takatoki Yamamoto
Micromachines 2018, 9(4), 186; https://doi.org/10.3390/mi9040186 - 15 Apr 2018
Cited by 11 | Viewed by 6151
Abstract
The application of subwavelength, textured structures to glass surfaces has been shown to reduce reflectivity and also results in self-cleaning due to super-hydrophobicity. However, current methods of producing such textures are typically either expensive or difficult to scale up. Based on prior work [...] Read more.
The application of subwavelength, textured structures to glass surfaces has been shown to reduce reflectivity and also results in self-cleaning due to super-hydrophobicity. However, current methods of producing such textures are typically either expensive or difficult to scale up. Based on prior work by the authors, the present study employed a combination of vacuum ultraviolet (VUV) light-assisted bonding and release agent-free pattern transfer to fabricate a moth-eye texture on a glass substrate. This was accomplished by forming a cyclic olefin polymer mold master with a moth-eye pattern, transferring this pattern to a polydimethylsiloxane (PDMS) spin coating, activating both the PDMS and a glass substrate with VUV light, and then bonding the PDMS to the glass before releasing the mold. Atomic force microscopy demonstrated that the desired pattern was successfully replicated on the PDMS surface with a high degree of accuracy, and the textured glass specimen exhibited approximately 3% higher transmittance than untreated glass. Contact angle measurements also showed that the hydrophobicity of the textured surface was significantly increased. These results confirm that this new technique is a viable means of fabricating optical nanostructures via a simple, inexpensive process. Full article
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<p>Unit cell employed as a finite element model of the inverted moth-eye structure in the COMSOL Multiphysics RF module.</p> Full article ">Figure 2
<p>(<b>a</b>) Simulated reflection spectrum of the inverted moth-eye structure at various depths (200–600 nm) and incident light wavelengths (400–700 nm) The color bar indicates the reflectance values. (<b>b</b>) Dependence of the calculated maximum reflectance (R_max) in the visible light region on the depth of the inverted moth-eye structure.</p> Full article ">Figure 3
<p>Schematic diagram of the VUV-assisted bonding and nanoscale pattern transfer process for fabricating the inverted moth-eye structure. (<b>a</b>) Spin-coating and curing of PDMS on a COP mold with a textured pattern, (<b>b</b>) surface activation of the glass and PDMS by VUV light, (<b>c</b>) bonding of the glass and the PDMS surfaces, and (<b>d</b>) release of the COP mold from the PDMS layer.</p> Full article ">Figure 4
<p>Schematic diagram of a liquid droplet on a textured surface similar to the inverted moth-eye structure, showing the parameters used to calculate the GFE density: (<b>a</b>) side-view, (<b>b</b>) enlarged top-view, and (<b>c</b>) enlarged side-view corresponding to the line in the top-view. Areas in deep blue indicate the ratio of the actual wetted area to the total solid area of the textured surface (<math display="inline"> <semantics> <mrow> <msub> <mi>r</mi> <mi>ϕ</mi> </msub> </mrow> </semantics> </math>), and red areas indicate the ratio of the actual area of liquid-solid contact to the projected area on the horizontal plane (<math display="inline"> <semantics> <mrow> <msub> <mi>ϕ</mi> <mi>s</mi> </msub> </mrow> </semantics> </math>).</p> Full article ">Figure 5
<p>AFM image of the COP mold.</p> Full article ">Figure 6
<p>AFM image of the inverted moth-eye structure made of PDMS.</p> Full article ">Figure 7
<p>Transmission spectrum of a glass substrate bonded to PDMS having an inverted moth-eye structure. The spectrum for glass and the simulated spectrum are shown for comparison purposes.</p> Full article ">Figure 8
<p>Contour maps (2D map:(a), 3D map:(b)) showing changes in the GFE density (In(<span class="html-italic">G</span>* − <span class="html-italic">G</span>*<span class="html-italic"><sub>min</sub></span>)) as a function of the estimated apparent contact angle (<math display="inline"> <semantics> <mrow> <msubsup> <mi>θ</mi> <mi>E</mi> <mo>*</mo> </msubsup> </mrow> </semantics> </math>) with the normalized position at the water-air interface (<span class="html-italic">Z</span>/<span class="html-italic">D</span>) in an inverted moth-eye structure made of PDMS (<math display="inline"> <semantics> <mrow> <mi>θ</mi> <mo>=</mo> <mn>100</mn> <mo>°</mo> </mrow> </semantics> </math>). The insert in the 2D map is a captured image of a water droplet on the inverted moth-eye structure. The blue region represents the global minimum in the GFE density.</p> Full article ">
22 pages, 2988 KiB  
Review
Research and Analysis of MEMS Switches in Different Frequency Bands
by Wenchao Tian, Ping Li and LinXiao Yuan
Micromachines 2018, 9(4), 185; https://doi.org/10.3390/mi9040185 - 15 Apr 2018
Cited by 42 | Viewed by 5462
Abstract
Due to their high isolation, low insertion loss, high linearity, and low power consumption, microelectromechanical systems (MEMS) switches have drawn much attention from researchers in recent years. In this paper, we introduce the research status of MEMS switches in different bands and several [...] Read more.
Due to their high isolation, low insertion loss, high linearity, and low power consumption, microelectromechanical systems (MEMS) switches have drawn much attention from researchers in recent years. In this paper, we introduce the research status of MEMS switches in different bands and several reliability issues, such as dielectric charging, contact failure, and temperature instability. In this paper, some of the following methods to improve the performance of MEMS switches in high frequency are summarized: (1) utilizing combinations of several switches in series; (2) covering a float metal layer on the dielectric layer; (3) using dielectric layer materials with high dielectric constants and conductor materials with low resistance; (4) developing MEMS switches using T-match and π-match; (5) designing MEMS switches based on bipolar complementary metal–oxide–semiconductor (BiCMOS) technology and reconfigurable MEMS’ surfaces; (6) employing thermal compensation structures, circularly symmetric structures, thermal buckle-beam actuators, molybdenum membrane, and thin-film packaging; (7) selecting Ultra-NanoCrystalline diamond or aluminum nitride dielectric materials and applying a bipolar driving voltage, stoppers, and a double-dielectric-layer structure; and (8) adopting gold alloying with carbon nanotubes (CNTs), hermetic and reliable packaging, and mN-level contact. Full article
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<p>The schematics of typical microelectromechanical systems (MEMS) switches: (<b>a</b>) shunt capacitive MEMS switch; (<b>b</b>) DC contact switch. Coplanar waveguide (CPW) = coplanar waveguide.</p> Full article ">Figure 2
<p>The novel capacitive MEMS switch with high capacitance ratio for multiband. Reprinted by permission from [<a href="#B36-micromachines-09-00185" class="html-bibr">36</a>].</p> Full article ">Figure 3
<p>The capacitive MEMS switch with asymmetrical cantilevers. Reprinted by permission from [<a href="#B40-micromachines-09-00185" class="html-bibr">40</a>].</p> Full article ">
17 pages, 22594 KiB  
Article
Topology Optimization of Spatially Compliant Mechanisms with an Isomorphic Matrix of a 3-UPC Type Parallel Prototype Manipulator
by Dachang Zhu, Wanghu Zhan, Fupei Wu and Alessandro Simeone
Micromachines 2018, 9(4), 184; https://doi.org/10.3390/mi9040184 - 14 Apr 2018
Cited by 10 | Viewed by 4669
Abstract
A novel topology optimization approach is proposed in this paper for the design of three rotational degree-of-freedom (DOF) spatially compliant mechanisms, combining the Jacobian isomorphic mapping matrix with the solid isotropic material with penalization (SIMP) topological method. In this approach, the isomorphic Jacobian [...] Read more.
A novel topology optimization approach is proposed in this paper for the design of three rotational degree-of-freedom (DOF) spatially compliant mechanisms, combining the Jacobian isomorphic mapping matrix with the solid isotropic material with penalization (SIMP) topological method. In this approach, the isomorphic Jacobian matrix of a 3-UPC (U: universal joint, P: prismatic joint, C: cylindrical joint) type parallel prototype manipulator is formulated. Subsequently, the orthogonal triangular decomposition and differential kinematic method is applied to uncouple the Jacobian matrix to construct a constraint for topology optimization. Firstly, with respect to the 3-UPC type parallel prototype manipulator, the Jacobian matrix is derived to map the inputs and outputs to be used for initializing the topology optimization process. Secondly, the orthogonal triangular decomposition with the differential kinematic method is used to reconstruct the uncoupled mapping matrix to derive the 3-UPC type parallel prototype manipulator. Finally, a combination of the solid isotropic material with penalization (SIMP) method and the isomorphic mapping matrix is applied to construct the topological model. A typical three rotational DOF spatially compliant mechanism is reported as a numerical example to demonstrate the effectiveness of the proposed method. Full article
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<p>3-UPC type parallel prototype manipulator (<b>a</b>) structure configuration model, (<b>b</b>) parameters with coordinate frame.</p> Full article ">Figure 2
<p>Initial design domain of the three-DOF spatially compliant mechanism.</p> Full article ">Figure 3
<p>Topology optimization structure of the three-DOF spatially compliant mechanism, (<b>a</b>) Structure of the three-DOF spatially compliant mechanism; (<b>b</b>) Top view of this structure.</p> Full article ">Figure 4
<p>Topology optimization iteration procedure of the three-DOF spatially compliant mechanism.</p> Full article ">Figure 5
<p>Structure of the 3-UPC type parallel prototype manipulator using SimMechanical<sup>@</sup> software.</p> Full article ">Figure 6
<p>Forward kinematic comparison between differential kinematic approximation method and actual model of the 3-UPC type parallel prototype manipulator.</p> Full article ">Figure 7
<p>Stress distribution comparison: (<b>a</b>) before optimization; (<b>b</b>) after optimization.</p> Full article ">Figure 7 Cont.
<p>Stress distribution comparison: (<b>a</b>) before optimization; (<b>b</b>) after optimization.</p> Full article ">Figure 8
<p>The three nano-scale-rotational displacements of the spatially compliant mechanism; (<b>a</b>) Along the <math display="inline"><semantics> <mi>x</mi> </semantics></math>-axis the maximum displacement is 7.774 × 10<sup>−7</sup> rad and the minimum displacement is −6.299 × 10<sup>−7</sup> rad; (<b>b</b>) Along the <math display="inline"><semantics> <mi>y</mi> </semantics></math>-axis the maximum displacement is 3.541 × 10<sup>−6</sup> rad and the minimum displacement is −2.299 × 10<sup>−7</sup> rad; (<b>c</b>) Along the <math display="inline"><semantics> <mi>z</mi> </semantics></math>-axis the maximum displacement is 4.344 × 10<sup>−6</sup> rad and the minimum displacement is 0 rad.</p> Full article ">Figure 8 Cont.
<p>The three nano-scale-rotational displacements of the spatially compliant mechanism; (<b>a</b>) Along the <math display="inline"><semantics> <mi>x</mi> </semantics></math>-axis the maximum displacement is 7.774 × 10<sup>−7</sup> rad and the minimum displacement is −6.299 × 10<sup>−7</sup> rad; (<b>b</b>) Along the <math display="inline"><semantics> <mi>y</mi> </semantics></math>-axis the maximum displacement is 3.541 × 10<sup>−6</sup> rad and the minimum displacement is −2.299 × 10<sup>−7</sup> rad; (<b>c</b>) Along the <math display="inline"><semantics> <mi>z</mi> </semantics></math>-axis the maximum displacement is 4.344 × 10<sup>−6</sup> rad and the minimum displacement is 0 rad.</p> Full article ">Figure 9
<p>Topological structure, controller and actuator. (<b>a</b>) The physical model of the topological structure, (<b>b</b>) Controller, (<b>c</b>) PZT actuator.</p> Full article ">Figure 10
<p>Experimental device.</p> Full article ">Figure 11
<p>Displacement of three rotational directions along <math display="inline"><semantics> <mrow> <mi>x</mi> <mo>−</mo> <mi>y</mi> <mo>−</mo> <mi>z</mi> </mrow> </semantics></math> axes; (<b>a</b>) Around <math display="inline"><semantics> <mi>x</mi> </semantics></math>-axis, (<b>b</b>) Around <math display="inline"><semantics> <mi>y</mi> </semantics></math>-axis, (<b>c</b>) Around <math display="inline"><semantics> <mi>z</mi> </semantics></math>-axis.</p> Full article ">Figure 12
<p>First order modal of the proposed spatially compliant mechanism with three-rotational-DOFs.</p> Full article ">Figure 13
<p>Second order modal of the proposed spatially compliant mechanism with three rotational DOFs.</p> Full article ">
19 pages, 2644 KiB  
Review
High-Throughput Optofluidic Acquisition of Microdroplets in Microfluidic Systems
by Zain Hayat and Abdel I. El Abed
Micromachines 2018, 9(4), 183; https://doi.org/10.3390/mi9040183 - 14 Apr 2018
Cited by 18 | Viewed by 7210
Abstract
Droplet optofluidics technology aims at manipulating the tiny volume of fluids confined in micro-droplets with light, while exploiting their interaction to create “digital” micro-systems with highly significant scientific and technological interests. Manipulating droplets with light is particularly attractive since the latter provides wavelength [...] Read more.
Droplet optofluidics technology aims at manipulating the tiny volume of fluids confined in micro-droplets with light, while exploiting their interaction to create “digital” micro-systems with highly significant scientific and technological interests. Manipulating droplets with light is particularly attractive since the latter provides wavelength and intensity tunability, as well as high temporal and spatial resolution. In this review study, we focus mainly on recent methods developed in order to monitor real-time analysis of droplet size and size distribution, active merging of microdroplets using light, or to use microdroplets as optical probes. Full article
(This article belongs to the Special Issue Advances in Optofluidics)
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<p>Droplet generation by microfluidic systems. (<b>a</b>) T-junction; (<b>b</b>) Flow-focusing; (<b>c</b>) Co-flow (glass capillary); (<b>d</b>) Droplet generation by flow focusing device (use of fluorinated oil with stabilizing agent and disperse phase as water solution of dye), device also includes on-chip storage pool for droplet collection and operation region.</p> Full article ">Figure 2
<p>(<b>top</b>) A typical dual channel microfluidic droplet monitoring setup, consisting of two laser sources with each laser band limited by a bandpass filter. The two components of the fluorescence signals emitted by the two different dyes are separated, filtered, and collected on two different photo-multiplier tubes (PMTs). (<b>bottom</b>) Typical recorded fluorescence intensity versus time emitted by flowing droplets containing both fluorescein and rhodamine dyes at different concentrations. DM: dichroic mirror.</p> Full article ">Figure 3
<p>Fluorescence signal extracts from setup (<b>a</b>) without surfactant; (<b>b</b>) with surfactant.</p> Full article ">Figure 4
<p>Fluorescence signal from microdroplets (<b>a</b>) in HFE7500–without surfactant; (<b>b</b>) with surfactant KryJeffa; (<b>c</b>) droplets stabilized in Krytox (size around 125 <math display="inline"> <semantics> <mi mathvariant="sans-serif">μ</mi> </semantics> </math>m); (<b>d</b>) big droplets with surfactant Krytox (size above 250 <math display="inline"> <semantics> <mi mathvariant="sans-serif">μ</mi> </semantics> </math>m); (<b>e</b>) plug-like deformation of a large droplet induced by flow of viscous oil; (<b>f</b>) heterogeneous distribution of surfactant at the droplet interface; (<b>g</b>) in the case of Krytox the distribution of surfactant and its corresponding interaction to charged rhodamine molecules at the rear of the microdroplet.</p> Full article ">Figure 4 Cont.
<p>Fluorescence signal from microdroplets (<b>a</b>) in HFE7500–without surfactant; (<b>b</b>) with surfactant KryJeffa; (<b>c</b>) droplets stabilized in Krytox (size around 125 <math display="inline"> <semantics> <mi mathvariant="sans-serif">μ</mi> </semantics> </math>m); (<b>d</b>) big droplets with surfactant Krytox (size above 250 <math display="inline"> <semantics> <mi mathvariant="sans-serif">μ</mi> </semantics> </math>m); (<b>e</b>) plug-like deformation of a large droplet induced by flow of viscous oil; (<b>f</b>) heterogeneous distribution of surfactant at the droplet interface; (<b>g</b>) in the case of Krytox the distribution of surfactant and its corresponding interaction to charged rhodamine molecules at the rear of the microdroplet.</p> Full article ">Figure 5
<p>Different studies for droplet generation monitoring: (<b>A</b>) A microdroplet megascale detector (<math display="inline"> <semantics> <mrow> <mi mathvariant="sans-serif">μ</mi> </mrow> </semantics> </math>MD) containing a micro-controller-based light emitting diode, a microfluidic device with 120 parallel dropmakers, a cell phone camera for recording, and an off-site data processor. Reproduced with permission from [<a href="#B39-micromachines-09-00183" class="html-bibr">39</a>]; (<b>B</b>) Experimental setup of the Integrated Comprehensive Droplet Digital Detection (IC 3D) system, housing 496 nm and 532 nm laser sources, a dual source single detector scheme modified for the typical experimental needs. A software controlled micro-cuvette holder and rotation unit (1–1100 rpm in rotational speed while 1–15 mm/s vertical translational speed). Reproduced with permission from [<a href="#B36-micromachines-09-00183" class="html-bibr">36</a>]; (<b>C</b>) A CMOS (complementary metal oxide semiconductor)-based sensor with channel bed as closest perimeter for fluorescence detection. The compact sensor assembly consists of a 1280 × 1024 pixel platform, a spin-coated pigment-based band-pass filter, a 250 mW blue LED, and another filter to band limit the light between 457 nm to 492 nm. Reproduced with permission from [<a href="#B34-micromachines-09-00183" class="html-bibr">34</a>]; (<b>D</b>) Integrated micro-optical system with micro-lens assemblies on top of droplet chambers while metallic surfaces at other side of chamber provide optical resonance for improved signal. Reproduced with permission from [<a href="#B38-micromachines-09-00183" class="html-bibr">38</a>]; (<b>E</b>) Experimental stage for digital polymerase chain reaction (PCR) housing a 1 × 256 droplet splitting microfluidic chip on a thermistor stage for PCR thermocycling, a wide field light source, and a digital camera with large field-of-view lens assembly. Reproduced with permission from [<a href="#B37-micromachines-09-00183" class="html-bibr">37</a>].</p> Full article ">Figure 6
<p>Optical droplets merging and sorting: (<b>a</b>) Square-shaped projection patterns moving two droplets towards each other, merged, and sliced back to acquire two droplets. Reproduced with permission from [<a href="#B135-micromachines-09-00183" class="html-bibr">135</a>]; (<b>b</b>) Time sequences of an elongated droplet sliced by on-chip Teflon blade, droplet motion assisted by line projection. Reproduced with permission from [<a href="#B136-micromachines-09-00183" class="html-bibr">136</a>].</p> Full article ">Figure 7
<p>Surfactants 1 and 2: (<b>a</b>) Chemical composition; (<b>b</b>) Interfacial tension versus concentration, red curve for Surfactant 1 and green curve for Surfactant 2; (<b>c</b>) Surface pressure versus molecular area; (<b>d</b>) Light-induced merging of droplets 1 and 2. Reproduced with permission from [<a href="#B32-micromachines-09-00183" class="html-bibr">32</a>].</p> Full article ">Figure 8
<p>Imaging using microdroplets: setup for light input from the top with an adjustable image plane, droplets on a substrate, image plane, and bottom collection objective with vertical translation, characteristic focal length tunability based on the morphology of the emulsion, and corresponding fully converging-to-fully diverging mechanism. Reproduced with permission from [<a href="#B63-micromachines-09-00183" class="html-bibr">63</a>].</p> Full article ">
9 pages, 2371 KiB  
Communication
Photopatternable Magnetic Hollowbots by Nd-Fe-B Nanocomposite for Potential Targeted Drug Delivery Applications
by Hui Li, Jing Chen, Jinjie Zhang, Jingyong Zhang, Guoru Zhao and Lei Wang
Micromachines 2018, 9(4), 182; https://doi.org/10.3390/mi9040182 - 13 Apr 2018
Cited by 4 | Viewed by 3982
Abstract
In contrast to traditional drug administration, targeted drug delivery can prolong, localize, target and have a protected drug interaction with the diseased tissue. Drug delivery carriers, such as polymeric micelles, liposomes, dendrimers, nanotubes, and so on, are hard to scale-up, costly, and have [...] Read more.
In contrast to traditional drug administration, targeted drug delivery can prolong, localize, target and have a protected drug interaction with the diseased tissue. Drug delivery carriers, such as polymeric micelles, liposomes, dendrimers, nanotubes, and so on, are hard to scale-up, costly, and have short shelf life. Here we show the novel fabrication and characterization of photopatternable magnetic hollow microrobots that can potentially be utilized in microfluidics and drug delivery applications. These magnetic hollowbots can be fabricated using standard ultraviolet (UV) lithography with low cost and easily accessible equipment, which results in them being easy to scale up, and inexpensive to fabricate. Contact-free actuation of freestanding magnetic hollowbots were demonstrated by using an applied 900 G external magnetic field to achieve the movement control in an aqueous environment. According to the movement clip, the average speed of the magnetic hollowbots was estimated to be 1.9 mm/s. Full article
(This article belongs to the Special Issue Locomotion at Small Scales: From Biology to Artificial Systems)
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<p>Recent magnetic micro-/nano- drug delivery systems. (<b>a</b>) The cyclo(Arg-Gly-Asp-D)-doxorubicin/verapamil-magnetic nanoparticles-Poly(lactic acid-coglycolic acid) nanoparticles. Reproduced with permission from [<a href="#B10-micromachines-09-00182" class="html-bibr">10</a>]. Copyright 2013, Elsevier; (<b>b</b>) An array of helical micromachines. Reproduced with permission from [<a href="#B9-micromachines-09-00182" class="html-bibr">9</a>]. Copyright 2012, John Wiley and Sons; (<b>c</b>) Heterogeneous rattle-type Fe<sub>3</sub>O<sub>4</sub>@mSiO<sub>2</sub> nanoparticles. Reproduced with permission from [<a href="#B11-micromachines-09-00182" class="html-bibr">11</a>]. Copyright 2011, The Royal Society of Chemistry; (<b>d</b>) Rattle-type magnetic mesoporous silica nanospheres. Reproduced with permission from [<a href="#B12-micromachines-09-00182" class="html-bibr">12</a>], Copyright 2011, The Royal Society of Chemistry; (<b>e</b>) Tissue plasminogen activator bound to silica-coated magnetic nanoparticle after staining with phosphotungstic acid. Reproduced with permission from [<a href="#B13-micromachines-09-00182" class="html-bibr">13</a>]; (<b>f</b>) Hollow core, magnetic, and mesoporous double-shell nanostructures. Reproduced with permission from [<a href="#B14-micromachines-09-00182" class="html-bibr">14</a>]. Copyright 2011, John Wiley and Sons; (<b>g</b>) An untethered artificial bacterial flagella. Reproduced with permission from [<a href="#B15-micromachines-09-00182" class="html-bibr">15</a>]. Copyright 2009, AIP Publishing.; (<b>h</b>) MagnetoSperm moving under the influence of the oscillating weak magnetic fields. Reproduced with permission from [<a href="#B16-micromachines-09-00182" class="html-bibr">16</a>]. Copyright 2014, AIP Publishing.</p> Full article ">Figure 2
<p>Schematic of magnetic hollowbots fabrication.</p> Full article ">Figure 3
<p>Scanning electron microscope (SEM) images of cylindrical (<b>a</b>) and cuboid (<b>b</b>) magnetic hollowbots before photopatterning top layer. (<b>c</b>) SEM image and sketch of the photopatterned magnetic cylindrical hollowbot structure. (<b>d</b>) SEM image of the photopatterned magnetic cuboid hollowbots. Scale bars = 100 µm.</p> Full article ">Figure 4
<p>Optical images of (<b>a</b>) 40%, 1000 rpm, (<b>b</b>) 40%, 4000 rpm samples.</p> Full article ">Figure 5
<p>(<b>a</b>–<b>d</b>) 10% mass fraction Nd-Fe-B composite uniformity for different fabrication spincoating speed. Histograms represent for samples at given processing parameters. (<b>e</b>–<b>h</b>) 40% mass fraction Nd-Fe-B composite uniformity for different fabrication spincoating speed. Histograms represent for samples at given processing parameters.</p> Full article ">Figure 6
<p>Captured images (every 2 s) from the clip of hollowbots actuated by external magnetic field in isopropyl alcohol. (<b>a</b>) 0 s; (<b>b</b>) 2 s; (<b>c</b>) 4 s; (<b>d</b>) 6 s; (<b>e</b>) 8 s; (<b>f</b>) 10 s.</p> Full article ">
13 pages, 4065 KiB  
Article
Bonding-Based Wafer-Level Vacuum Packaging Using Atomic Hydrogen Pre-Treated Cu Bonding Frames
by Koki Tanaka, Hideki Hirano, Masafumi Kumano, Joerg Froemel and Shuji Tanaka
Micromachines 2018, 9(4), 181; https://doi.org/10.3390/mi9040181 - 13 Apr 2018
Cited by 4 | Viewed by 4840
Abstract
A novel surface activation technology for Cu-Cu bonding-based wafer-level vacuum packaging using hot-wire-generated atomic hydrogen treatment was developed. Vacuum sealing temperature at 300 °C was achieved by atomic hydrogen pre-treatment for Cu native oxide reduction, while 350 °C was needed by the conventional [...] Read more.
A novel surface activation technology for Cu-Cu bonding-based wafer-level vacuum packaging using hot-wire-generated atomic hydrogen treatment was developed. Vacuum sealing temperature at 300 °C was achieved by atomic hydrogen pre-treatment for Cu native oxide reduction, while 350 °C was needed by the conventional wet chemical oxide reduction procedure. A remote-type hot-wire tool was employed to minimize substrate overheating by thermal emission from the hot-wire. The maximum substrate temperature during the pre-treatment is lower than the temperature of Cu nano-grain re-crystallization, which enhances Cu atomic diffusion during the bonding process. Even after 24 h wafer storage in atmospheric conditions after atomic hydrogen irradiation, low-temperature vacuum sealing was achieved because surface hydrogen species grown by the atomic hydrogen treatment suppressed re-oxidation. Vacuum sealing yield, pressure in the sealed cavity and bonding shear strength by atomic hydrogen pre-treated Cu-Cu bonding are 90%, 5 kPa and 100 MPa, respectively, which are equivalent to conventional Cu-Cu bonding at higher temperature. Leak rate of the bonded device is less than 10−14 Pa m3 s−1 order, which is applicable for practical use. The developed technology can contribute to low-temperature hermetic packaging. Full article
(This article belongs to the Special Issue Wafer Level Packaging of MEMS)
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<p>Schematic of the remote-type hot-wire tool.</p> Full article ">Figure 2
<p>Fabrication processes of (<b>a</b>) the top wafer (cavity wafer), (<b>b</b>) the bottom wafer (bonding frame wafer) and (<b>c</b>) bonded wafer. Both wafer size is 2 cm square. Each wafer has 16 cavities with diaphragms and bonding frames.</p> Full article ">Figure 3
<p>Schematic of the sealed cavity pressure evaluation by zero-balance method.</p> Full article ">Figure 4
<p>Schematic of bonding shear strength evaluation.</p> Full article ">Figure 5
<p>Yields of the hermetic sealed cavities. A pair of bonding wafers is exposed to the atmosphere for 1 h after each pre-treatment. (<b>a</b>) Citric acid treated wafer. (<b>b</b>) Atomic hydrogen treated wafer.</p> Full article ">Figure 6
<p>Shear strengths of the bonded chips.</p> Full article ">Figure 7
<p>Hermetic sealed cavities pressure measured by zero-balance method.</p> Full article ">Figure 8
<p>Cavity pressure change with air exposure time. (<b>a</b>) Citric acid treated wafer, which was bonded at 350 °C. (<b>b</b>) Atomic hydrogen treated wafer, which was bonded at 300 °C.</p> Full article ">Figure 9
<p>AES spectra of the treated Cu films after exposed to the air for 1 or 24 h. (<b>a</b>) Citric acid treated Cu film. (<b>b</b>) Atomic hydrogen treated Cu film.</p> Full article ">Figure 10
<p>TDS spectra of the treated Cu films after exposed to the atmosphere for 1 h. (<b>a</b>) Citric acid treated Cu film. (<b>b</b>) Atomic hydrogen treated Cu film.</p> Full article ">Figure 11
<p>Total amounts of desorbed molecules in the TDS measurements. The treated Cu films are exposed to the atmosphere for 1 or 24 h. (<b>a</b>) Citric acid treated Cu film. (<b>b</b>) Atomic hydrogen treated Cu film.</p> Full article ">
9 pages, 10663 KiB  
Article
Quantitative Evaluation of Dielectric Breakdown of Silicon Micro- and Nanofluidic Devices for Electrophoretic Transport of a Single DNA Molecule
by Mamiko Sano, Noritada Kaji, Qiong Wu, Toyohiro Naito, Takao Yasui, Masateru Taniguchi, Tomoji Kawai and Yoshinobu Baba
Micromachines 2018, 9(4), 180; https://doi.org/10.3390/mi9040180 - 13 Apr 2018
Cited by 4 | Viewed by 3897
Abstract
In the present study, we quantitatively evaluated dielectric breakdown in silicon-based micro- and nanofluidic devices under practical electrophoretic conditions by changing the thickness of the insulating layer. At higher buffer concentration, a silicon nanofluidic device with a 100 nm or 250 nm silicon [...] Read more.
In the present study, we quantitatively evaluated dielectric breakdown in silicon-based micro- and nanofluidic devices under practical electrophoretic conditions by changing the thickness of the insulating layer. At higher buffer concentration, a silicon nanofluidic device with a 100 nm or 250 nm silicon dioxide layer tolerated dielectric breakdown up to ca. 10 V/cm, thereby allowing successful electrophoretic migration of a single DNA molecule through a nanochannel. The observed DNA migration behavior suggested that parameters, such as thickness of the insulating layer, tolerance of dielectric breakdown, and bonding status of silicon and glass substrate, should be optimized to achieve successful electrophoretic transport of a DNA molecule through a nanopore for nanopore-based DNA sequencing applications. Full article
(This article belongs to the Special Issue State-of-the-Art Lab-on-a-Chip Technology in Japan)
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<p>Microfluidic devices for dielectric breakdown experiments (<b>A</b>–<b>C</b>) and a nanofluidic device for single DNA molecule observation (<b>D</b>–<b>G</b>). (<b>A</b>–<b>C</b>) Image of microfluidic devices with (<b>A</b>) natural oxide (NO) layer, (<b>B</b>) 100 nm thick, and (<b>C</b>) 250 nm thick silicon dioxide layer on the surface of silicon substrate formed via CVD. The dimension of all the microchannels were; 200 μm in width, 2 μm in depth, and 1 cm in length. (<b>D</b>) Image of the nanofluidic devices. Micro- and nanochannels were fabricated on a silicon substrate and covered with glass via anodic bonding. (<b>E</b>) Schematic illustration of the micro- and nanochannels and the electrodes setup. (<b>F</b>) Optical microscope image of the nanochannels bridging two wide microchannels. The highlighted region by yellow indicates the area fabricated by EB lithography. (<b>G</b>) Scanning electron microscope image of the nanochannels. Both the width and the depth of the nanochannels are 100 nm and the length is 10 μm.</p> Full article ">Figure 2
<p>Representative time courses of the applied voltage (red line) and the channel currents (blue line) on the silicon microchannels with the following varying oxide layer thicknesses: (<b>A</b>) NO, (<b>B</b>) 100 nm, and (<b>C</b>) 250 nm. In all experiments, channels were filled with 1× TBE, and applied electric fields were raised by 1 V every 2 s from 0 to 15 V. Channel currents were monitored using an ampere meter embedded in the high voltage sequencer. Current measurements were performed in two separate measurements using a single device, namely, from 0 to 7 V and from 8 to 15 V, due to limitations in the programmable voltage sequencer. Therefore, presented values are combined data from the two sets of measurements.</p> Full article ">Figure 3
<p>Monitored time-average currents were plotted as a function of the applied voltage. (<b>A</b>) NO, (<b>B</b>) 100 nm, and (<b>C</b>) 250 nm thick oxide layers on the silicon microchannels were filled with 5× TBE. Currents were measured in nine distinct devices, which are depicted in red, blue, and green circles, respectively. Dotted lines show theoretical currents under the assumption that no dielectric breakdown occurs and an electrical current pass through a microchannel.</p> Full article ">Figure 4
<p>Average voltage applied at the time of dielectric breakdown under different oxide layer thicknesses and buffer concentrations (<span class="html-italic">n</span> = 3). At the same concentration of TBE buffer, three plots and error bars depicted in red, blue, and green were intentionally shifted, so as to be easily seen.</p> Full article ">Figure 5
<p>(<b>A</b>) Electrophoretic migration behavior of a single T4 DNA molecule in a 100 nm wide and 100 nm deep nanochannel, which is arrayed continuously side-by-side with 400 nm spacing inside dashed white lines. An electric field of around a few V/cm was applied horizontally along the nanochannels. (<b>B</b>) Presumed DNA conformation is depicted as a black line in the right for clarity. The folded and twisted parts, indicated by arrows, could be caused by defects in the silicon dioxide layer during anodic bonding. The DNA molecule appears to switch the nanochannel vertically during migration.</p> Full article ">
24 pages, 7413 KiB  
Article
On Developing Field-Effect-Tunable Nanofluidic Ion Diodes with Bipolar, Induced-Charge Electrokinetics
by Ye Tao, Weiyu Liu, Yukun Ren, Yansu Hu, Guang Li, Guoyun Ma and Qisheng Wu
Micromachines 2018, 9(4), 179; https://doi.org/10.3390/mi9040179 - 12 Apr 2018
Cited by 10 | Viewed by 4691
Abstract
We introduce herein the induced-charge electrokinetic phenomenon to nanometer fluidic systems; the design of the nanofluidic ion diode for field-effect ionic current control of the nanometer dimension is developed by enhancing internal ion concentration polarization through electrochemical transport of inhomogeneous inducing-counterions resulting from [...] Read more.
We introduce herein the induced-charge electrokinetic phenomenon to nanometer fluidic systems; the design of the nanofluidic ion diode for field-effect ionic current control of the nanometer dimension is developed by enhancing internal ion concentration polarization through electrochemical transport of inhomogeneous inducing-counterions resulting from double gate terminals mounted on top of a thin dielectric layer, which covers the nanochannel connected to microfluidic reservoirs on both sides. A mathematical model based on the fully-coupled Poisson-Nernst-Plank-Navier-Stokes equations is developed to study the feasibility of this structural configuration causing effective ionic current rectification. The effect of various physiochemical and geometrical parameters, such as the native surface charge density on the nanochannel sidewalls, the number of gate electrodes (GE), the gate voltage magnitude, and the solution conductivity, permittivity, and thickness of the dielectric coating, as well as the size and position of the GE pair of opposite gate polarity, on the resulted rectification performance of the presented nanoscale ionic device is numerically analyzed by using a commercial software package, COMSOL Multiphysics (version 5.2). Three types of electrohydrodynamic flow, including electroosmosis of 1st kind, induced-charge electroosmosis, and electroosmosis of 2nd kind that were originated by the Coulomb force within three distinct charge layers coexist in the micro/nanofluidic hybrid network and are shown to simultaneously influence the output current flux in a complex manner. The rectification factor of a contrast between the ‘on’ and ‘off’ working states can even exceed one thousand-fold in the case of choosing a suitable combination of several key parameters. Our demonstration of field-effect-tunable nanofluidic ion diodes of double external gate electrodes proves invaluable for the construction of a flexible electrokinetic platform for ionic current control and may help transform the field of smart, on-chip, integrated circuits. Full article
(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics, Volume II)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>2D Schematics of electrical manipulation strategy for the two distinct working statuses and rectification mechanism of output ionic current <span class="html-italic">I</span><sub>output</sub> of the presented nanofluidic ion diode with double GEs laid on top of a dielectric coating layer to close the nanochannel of negative wall charge. (<b>a</b>) Geometric configuration of the nano-scale device. (<b>b</b>,<b>c</b>) Under positive V<sub>G1</sub> and negative V<sub>G2</sub>; (<b>b</b>) the output current flux <span class="html-italic">I</span><sub>output</sub> towards the downstream microchamber is inhibited under a positive value of Vs &gt; 0, in that an ion depletion zone is produced in the central district by the vast transport of induced counterions toward adjacent reservoirs, i.e., the ‘off’ status; and (<b>c</b>) <span class="html-italic">I</span><sub>output</sub> towards the upstream reservoir can be switched on with a negative value of Vs &lt; 0, since stable ion enrichment is induced at the midchannel due to fast inward translation of induced counterions to the central region covered by the physical gap between the double GE.</p> Full article ">Figure 2
<p>A surface plot of dimensionless ion concentration distribution (<span class="html-italic">C</span><sub>+</sub> + <span class="html-italic">C</span><sub>−</sub>)/2<span class="html-italic">C</span><sub>0</sub> in two different electrode configurations for opposite working status of the proposed nanofluidic ion diode. (<b>a</b>,<b>b</b>) In the ionic device with single gate electrode mounted on the left of the top of the dielectric layer: (<b>a</b>) concentration field in the forward ‘off’ status in which the ionic current is blocked by the central desalinated area, and (<b>b</b>) the backward ‘on’ working state, in which the ionic current is enhanced by the central concentrated portion. (<b>c</b>,<b>d</b>) In stark contrast with the situation of merely one gate, the phenomenon of ion concentration polarization is made stronger and more stable in the structural design of ionic device with double gate electrodes laid on both sides of the dielectric layer surface; (<b>c</b>) as the applied field runs toward the D terminal, a low ion conductance at the channel center forbids any current flow in the forward direction, that is, the ‘off’ working state; and (<b>d</b>) with a reversal in the direction of imposed voltage gradient, the output current <span class="html-italic">I</span><sub>ouput</sub> toward the S terminal is intensified to great extent by the well-developed ion-enrichment zone inside the nanochannel.</p> Full article ">Figure 3
<p>A quantitative comparison study between the rectification performance of the ionic device with single and double gate terminals for the given values of gate voltages V<sub>G1</sub> = −V<sub>G2</sub> = 10 V. (<b>a</b>) Output current flow <span class="html-italic">I</span><sub>output</sub> as a function of the source voltage Vs; (<b>b</b>) rectification factor of ionic current flux in reverse directions for the contrast between ‘on’ and ‘off’ status at varying magnitude of Vs; (<b>c</b>) nondimensional centerline concentration distribution of electrolyte charge carriers along nanochannel length direction for Vs = 4 V, in which the ionic species are sharply depleted in the central region, which appears to be more severe in the double GE design; (<b>d</b>) centerline ion density field for Vs = −4 V, in which a large amount of counterions are accumulated in the midchannel, and this ion-enrichment phenomenon takes place more appreciably for the advanced device design.</p> Full article ">Figure 4
<p>Simulation analysis of the influence of gate voltage magnitude on the device performance of the double-gate nanofluidic ion diode: (<b>a</b>) output ionic current as a function of gate voltage and (<b>b</b>) V<sub>G</sub>-dependent rectification factor for a source voltage contrast between V<sub>S</sub> = 4 V and V<sub>S</sub> = −4 V.</p> Full article ">Figure 5
<p>V<sub>G1</sub> = V<sub>G2</sub> = −12 V: influence of surface charge density distribution on diode functionality of the nanofluidic device. (<b>a</b>) Output current flux as a function of <span class="html-italic">σ<sub>free</sub></span> in reversed working status of the nano-dimensional device for V<sub>S</sub> = 4 V and V<sub>S</sub> = −4 V and (<b>b</b>) <span class="html-italic">σ<sub>free</sub></span>-dependent rectification performance of the ionic diode.</p> Full article ">Figure 6
<p>Effect of buffer ionic conductivity on the field-effect current control at nanometer dimension: (<b>a</b>) ion concentration-dependent <span class="html-italic">I</span><sub>output</sub> for reversed device working states; (<b>b</b>) rectification factor as a function of the medium conductivity.</p> Full article ">Figure 7
<p>Simulation analysis of the effect of dielectric layer thickness on nanodevice performance for voltage combinations of V<sub>S</sub> = ±4 V and V<sub>G1</sub> = −V<sub>G2</sub> = 15 V: (<b>a</b>) thickness-dependent output ionic current for both ‘on’ and ‘off’ working states; (<b>b</b>) rectification factor as a function of the thickness of insulating coating.</p> Full article ">Figure 8
<p>Effect of dielectric permittivity of the thin insulation layer on rectification performance of the nanofluidic ion diode: (<b>a</b>) permittivity-dependent output ionic current for both ‘on’ and ‘off’ working states; (<b>b</b>) rectification factor as a function of relative permittivity of the dielectric coating.</p> Full article ">Figure 9
<p>On the effect of GE size on the device performance: (<b>a</b>) <span class="html-italic">I</span><sub>output</sub> for reversed working states of the nanofluidic ion diode; (<b>b</b>) rectification factor as a function of GE width; (<b>c</b>) internal depleted ion concentration distribution for the forward ‘off’ status with V<sub>S</sub> = 4 V; (<b>d</b>) internal enriched distribution of charge carriers for backward ‘on’ status with V<sub>S</sub> = −4 V.</p> Full article ">Figure 10
<p>Effect of the location of double gate terminals on the resulted nanodevice performance. (<b>a</b>) The output current flux under reversed working states at V<sub>S</sub> = ±4 V; (<b>b</b>) rectification factor as a function of the horizontal position of GE (L<sub>D</sub>). (<b>c</b>–<b>f</b>) A surface plot of dimensionless concentration distribution of charge carriers for the backward ‘on’ status at Vs = −4V with different electrode positions, at (<b>c</b>) L<sub>D</sub> = 10 nm, (<b>d</b>) L<sub>D</sub> = 50 nm, (<b>e</b>) L<sub>D</sub> = 150 nm, and (f) L<sub>D</sub> = 280 nm.</p> Full article ">Figure 11
<p>A simulation analysis of the effect of different kinds of electroosmotic flow and ion concentration polarization in the micrometer-scale reservoirs on ionic current rectification of the nanofluidic ion diode. (<b>a</b>) For V<sub>S</sub> = −18 V, V<sub>G1</sub> = −V<sub>G2</sub> = 15 V, the ion-depletion zones induced in microchambers due to mismatch of charge carriers at the micro/nanofluidic interfaces arouse vortex flow field of 2nd electroosmosis with oppositely rotating directions on both sides, in which only the left reservoir is presented with its counterpart on right side not shown; (<b>b</b>) rectification performance of the nanodevice as a function of V<sub>S</sub>; (<b>c</b>) quantification on electroconvective flow velocity of 1st EOF and ICEO inside the nanochannel, as well as 2nd EOF in reservoirs on both sides as a function of V<sub>S</sub>; (<b>d</b>) V<sub>S</sub>-dependent characteristic ion density in the microchambers (concentrations of charge carriers are identical in reservoirs on both sides).</p> Full article ">Figure 12
<p>Distribution of axial electric field along the nanochannel centerline for different values of the source voltage V<sub>S</sub>.</p> Full article ">
11 pages, 30026 KiB  
Article
Fabrication Technology and Characteristics Research of the Acceleration Sensor Based on Li-Doped ZnO Piezoelectric Thin Films
by Sen Li, Xiaofeng Zhao, Yinan Bai, Yi Li, Chunpeng Ai and Dianzhong Wen
Micromachines 2018, 9(4), 178; https://doi.org/10.3390/mi9040178 - 12 Apr 2018
Cited by 12 | Viewed by 4178
Abstract
An acceleration sensor based on piezoelectric thin films is proposed in this paper, which comprises the elastic element of a silicon cantilever beam and a piezoelectric structure with Li-doped ZnO piezoelectric thin films. The Li-doped ZnO piezoelectric thin films were prepared on SiO [...] Read more.
An acceleration sensor based on piezoelectric thin films is proposed in this paper, which comprises the elastic element of a silicon cantilever beam and a piezoelectric structure with Li-doped ZnO piezoelectric thin films. The Li-doped ZnO piezoelectric thin films were prepared on SiO2/Si by radio frequency (RF) magnetron sputtering method. The microstructure and micrograph of ZnO piezoelectric thin films is analysed by a X-ray diffractometer (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and piezoresponse force microscopy (PFM), respectively. When the sputtering power of 220 W and Li-doped concentration of 5%, ZnO piezoelectric thin films have a preferred (002) orientation. The chips of the sensor were fabricated on the <100> silicon substrate by micro-electromechanical systems (MEMS) technology, meanwhile, the proposed sensor was packaged on the printed circuit board (PCB). The experimental results show the sensitivity of the proposed sensor is 29.48 mV/g at resonant frequency (1479.8 Hz). Full article
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<p>Basic structure of the acceleration sensor: (<b>a</b>) front view; (<b>b</b>) back view.</p> Full article ">Figure 2
<p>The operating principle of the Li-doped ZnO piezoelectric thin films acceleration sensor.</p> Full article ">Figure 3
<p>The main fabrication technology process of the proposed sensor: (<b>a</b>) the cleaning of the silicon wafer; (<b>b</b>) the releasing of the cantilever beam; (<b>c</b>) the growing of the Pt/Ti bottom electrode layer; (<b>d</b>) the sputtering of the Li-doped ZnO piezoelectric layer; (<b>e</b>) the evaporating the of Al top electrode layer.</p> Full article ">Figure 4
<p>The chip photos of acceleration sensor: (<b>a</b>) photo of chip; (<b>b</b>) photo of packaging chip.</p> Full article ">Figure 5
<p>The X-ray diffractometer (XRD) patterns of the Li-doped ZnO thin films: (<b>a</b>) under different Li doping concentrations; (<b>b</b>) under different sputtering powers.</p> Full article ">Figure 6
<p>X-ray photoelectron spectroscopy (XPS) spectra of 5 wt% Li-doped ZnO thin films (<b>a</b>) XPS spectra for Zn 2p; (<b>b</b>) narrow scan at Li 1s peak.</p> Full article ">Figure 7
<p>Scanning electron microscope (SEM) images of the Li-doped ZnO thin films under different sputtering powers: (<b>a</b>) 140 W; (<b>b</b>) 180 W; (<b>c</b>) 220 W; (<b>d</b>) 260 W.</p> Full article ">Figure 8
<p>Piezoresponse force microscopy (PFM) images of 5 wt% Li-doped ZnO thin films: (<b>a</b>) the two-dimensional topography; (<b>b</b>) the three-dimensional topography; (<b>c</b>) the relationship curve between stylus tip displacement and excitation voltages.</p> Full article ">Figure 9
<p>The testing system of the acceleration sensor.</p> Full article ">Figure 10
<p>The relationship curve between output voltage and excitation frequencies.</p> Full article ">Figure 11
<p>Piezoelectric characteristics curves of the sensor under different accelerations: (<b>a</b>) the output voltage waveforms of piezoelectric response; (<b>b</b>) the relationship curves between output voltage and <span class="html-italic">a</span>.</p> Full article ">
13 pages, 3823 KiB  
Article
Microfluidic Line-Free Mass Sensor Based on an Antibody-Modified Mechanical Resonator
by Masaki Yamaguchi
Micromachines 2018, 9(4), 177; https://doi.org/10.3390/mi9040177 - 12 Apr 2018
Cited by 3 | Viewed by 3565
Abstract
This research proposes a mass sensor based on mechanical resonance that is free from power supply lines (line-free) and incorporates both microfluidic mechanisms and label-free techniques to improve its sensitivity and reusability. The microfluidic line-free mass sensor comprises a disk-shaped mechanical resonator, a [...] Read more.
This research proposes a mass sensor based on mechanical resonance that is free from power supply lines (line-free) and incorporates both microfluidic mechanisms and label-free techniques to improve its sensitivity and reusability. The microfluidic line-free mass sensor comprises a disk-shaped mechanical resonator, a separate piezoelectric element used to excite vibrations in the resonator, and a microfluidic mechanism. Electrical power is used to actuate the piezoelectric element, leaving the resonator free from power lines. The microfluidic mechanism allows for rapid, repeat washings to remove impurities from a sample. The microfluidic line-free mass sensor is designed as a label-free sensor to enable high-throughput by modifying and dissociating an antibody on the resonator. The resonator was fabricated by photolithography and the diameter and thickness were 4 mm and 0.5 mm, respectively. The line-free mass sensor enabled a high Q-factor and resonance frequency of 7748 MHz and 1.402 MHz, respectively, to be achieved even in liquids, facilitating the analysis of human salivary cortisol. The line-free mass sensor could be used for repeated measurements with the microfluidic mechanism, and the resonator could be fully washed out. It was concluded that the microfluidic line-free mass sensor was suitable to analyze the concentration of a salivary hormone, cortisol, in human saliva samples, and that it provided high-throughput suitable for point-of-care testing. Full article
(This article belongs to the Special Issue Microfluidic Sensors)
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<p>Block diagram of a line-free mass sensor and the resonance frequency measuring system. Electrical power is used to actuate the piezoelectric element, leaving the line-free mass sensor free from power lines.</p> Full article ">Figure 2
<p>Schematic of immobilization of the antibody and the principle of the line-free mass sensor using the microfluidic mechanism (the schematic is not drawn to scale).</p> Full article ">Figure 3
<p>Proposed disk-shaped resonator.</p> Full article ">Figure 4
<p>Photolithography with deep-etching of the disk-shaped resonator, including a two-step exposure process using layout masks A and B.</p> Full article ">Figure 5
<p>Disk-shaped resonator fabricated by photolithography (<span class="html-italic">d</span> = 4 mm, <span class="html-italic">d</span><sub>c</sub> = 0.5 mm, <span class="html-italic">h</span> = 0.5 mm, <span class="html-italic">h</span><sub>c</sub> = 0.1 mm).</p> Full article ">Figure 6
<p>Resonance characteristics of the fabricated disk-shaped resonator at room temperature (25 °C).</p> Full article ">Figure 7
<p>Relationship between the frequency shift, Δ<span class="html-italic">f</span>, and the mass of anti-cortisol antibody, <span class="html-italic">x</span> (1.402 MHz measured frequency).</p> Full article ">Figure 8
<p>Influence of the temperature of reaction chamber, <span class="html-italic">T</span>, on the frequency shift, Δ<span class="html-italic">f</span> (1.402 MHz measured frequency).</p> Full article ">Figure 9
<p>Relationship between the frequency shift, Δ<span class="html-italic">f</span>, and the volume of washing buffer, <span class="html-italic">V</span> (1.402 MHz measured frequency).</p> Full article ">Figure 10
<p>Results of repeated evaluation when immunoreaction and dissociation were performed using one disk-shaped resonator (1.402 MHz measured frequency).</p> Full article ">Figure 11
<p>Calibration curves of standard cortisol samples in distilled water and model saliva as solvents (1.402 MHz measured frequency, 200 μL sample solution).</p> Full article ">Figure 12
<p>Scatter plot visualizing correlation of cortisol concentrations between a conventional assay (enzyme-linked immunosorbent assay (ELISA) method) and the fabricated line-free mass sensor in the use of human saliva samples.</p> Full article ">
19 pages, 8369 KiB  
Article
Mechanical Response of MEMS Inductor with Auxiliary Pillar under High-g Shock
by Lixin Xu, Yiyuan Li, Jianhua Li and Chongying Lu
Micromachines 2018, 9(4), 176; https://doi.org/10.3390/mi9040176 - 11 Apr 2018
Cited by 3 | Viewed by 3642
Abstract
Micro-electromechanical system (MEMS) suspended inductors have excellent radio-frequency (RF) performance, but poor mechanical properties. To improve their reliability, auxiliary pillars have been used. However, few studies have been carried out on the response of a suspended inductor with auxiliary pillars under high mechanical [...] Read more.
Micro-electromechanical system (MEMS) suspended inductors have excellent radio-frequency (RF) performance, but poor mechanical properties. To improve their reliability, auxiliary pillars have been used. However, few studies have been carried out on the response of a suspended inductor with auxiliary pillars under high mechanical shock. In this paper, a theoretical method is proposed that combines a single-degree-of-freedom (SDOF) model and a method for solving statically indeterminate structures. The calculated results obtained by this proposed method were verified by finite-element analysis (ANSYS). The calculated results obtained by the proposed method were found to agree well with the results of ANSYS simulation. Finally, this method was extended to a suspended inductor with double auxiliary pillars. The method proposed in this paper provides a theoretical reference for mechanical performance evaluation and reliability optimization design for MEMS suspended inductors with auxiliary pillars. Full article
(This article belongs to the Section A：Physics)
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<p>Schematic of the MEMS suspended inductor with auxiliary pillar.</p> Full article ">Figure 2
<p>Parameters of the suspended inductor.</p> Full article ">Figure 3
<p>Half-sine acceleration pulse.</p> Full article ">Figure 4
<p>SDOF model of the MEMS suspended inductor.</p> Full article ">Figure 5
<p>Top view of Part 1 of the coil.</p> Full article ">Figure 6
<p>Generalized forces added on the released end.</p> Full article ">Figure 7
<p>Critical stress location of the inductor coil.</p> Full article ">Figure 8
<p>Absolute acceleration response of each part of the suspended inductor with auxiliary pillar: (<b>a</b>) τ = 10 μs, (<b>b</b>) τ = 500 μs.</p> Full article ">Figure 9
<p>Maximum Von Mises equivalent stress of the inductor under two kinds of shock pulse. (<b>a</b>) Part 1; (<b>b</b>) Part 2.</p> Full article ">Figure 10
<p>Maximum Von Mises equivalent stress by ANSYS and the model versus shock load amplitude.</p> Full article ">Figure 11
<p>Maximum inductor deformation under two kinds of shock pulses. (<b>a</b>) Part 1; (<b>b</b>) Part 2.</p> Full article ">Figure 11 Cont.
<p>Maximum inductor deformation under two kinds of shock pulses. (<b>a</b>) Part 1; (<b>b</b>) Part 2.</p> Full article ">Figure 12
<p>Maximum deformations as calculated by ANSYS and the proposed model versus shock load amplitude.</p> Full article ">Figure 13
<p>Schematic of MEMS suspended inductor with double auxiliary pillars.</p> Full article ">Figure 14
<p>Top view of Part 1 of the coil.</p> Full article ">Figure 15
<p>Maximum Von Mises equivalent stress as calculated by ANSYS and the proposed model versus shock load amplitude.</p> Full article ">Figure 16
<p>Maximum deformation as calculated by ANSYS and the proposed model versus shock load amplitude.</p> Full article ">Figure 17
<p>Quality factors of the inductors with single and double auxiliary pillar(s).</p> Full article ">Figure 18
<p>Inductances of the inductors with single and double auxiliary pillar(s).</p> Full article ">
19 pages, 21705 KiB  
Article
Microfabricated Vapor Cells with Reflective Sidewalls for Chip Scale Atomic Sensors
by Runqi Han, Zheng You, Fan Zhang, Hongbo Xue and Yong Ruan
Micromachines 2018, 9(4), 175; https://doi.org/10.3390/mi9040175 - 11 Apr 2018
Cited by 18 | Viewed by 6333
Abstract
We investigate the architecture of microfabricated vapor cells with reflective sidewalls for applications in chip scale atomic sensors. The optical configuration in operation is suitable for both one-beam and two-beam (pump & probe) schemes. In the miniaturized vapor cells, the laser beam is [...] Read more.
We investigate the architecture of microfabricated vapor cells with reflective sidewalls for applications in chip scale atomic sensors. The optical configuration in operation is suitable for both one-beam and two-beam (pump & probe) schemes. In the miniaturized vapor cells, the laser beam is reflected twice by the aluminum reflectors on the wet etched 54.7° sidewalls to prolong the optical length significantly, thus resulting in a return reflectance that is three times that of bare silicon sidewalls. To avoid limitations faced in the fabrication process, a simpler, more universal and less constrained fabrication process of microfabricated vapor cells for chip scale atomic sensors with uncompromised performance is implemented, which also decreases the fabrication costs and procedures. Characterization measurements show that with effective sidewall reflectors, mm3 level volume and feasible hermeticity, the elongated miniature vapor cells demonstrate a linear absorption contrast improvement by 10 times over the conventional micro-electro-mechanical system (MEMS) vapor cells at ~50 °C in the rubidium D1 absorption spectroscopy experiments. At the operating temperature of ~90 °C for chip scale atomic sensors, a 50% linear absorption contrast enhancement is obtained with the reflective cell architecture. This leads to a potential improvement in the clock stability and magnetometer sensitivity. Besides, the coherent population trapping spectroscopy is applied to characterize the microfabricated vacuum cells with 46.3 kHz linewidth in the through cell configuration, demonstrating the effectiveness in chip scale atomic sensors. Full article
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<p>Optical configurations of (<b>a</b>) single light passing through the cell cavity and (<b>b</b>) round-trip light pass with folded optics.</p> Full article ">Figure 2
<p>Integration architecture schematic for chip scale atomic sensors with redirected laser beams in microfabricated vapor cells. The red light represents the pump beam and the green light is the probe beam. BS: Beam splitter.</p> Full article ">Figure 3
<p>Bulk silicon microfabrication and alkali metal operation processes of miniature vapor cells with reflective aluminum sidewalls.</p> Full article ">Figure 4
<p>(<b>a</b>) Photo of rubidium dispenser activation setup with a laser, a lens and a charge coupled device (CCD); (<b>b</b>) Zoom-in photo of rubidium dispenser activation process.</p> Full article ">Figure 5
<p>Cell photo of (<b>a</b>) 5 mm and (<b>b</b>) 10 mm long reflective optical length compared with 1 RMB coin.</p> Full article ">Figure 6
<p>Scanning electron microscope (SEM) micrographs of sidewalls viewed from the top surface and cross section (inset).</p> Full article ">Figure 7
<p>Through-cell absorption spectroscopy of rubidium D1 transition at different temperatures and the through-cell optical configuration (inset).</p> Full article ">Figure 8
<p>Reflectance of microfabricated silicon and aluminum reflectors at 795 nm.</p> Full article ">Figure 9
<p>Rubidium D1 line absorption spectroscopy with 5 mm long return reflection at different temperatures and the return reflection optical configuration (inset).</p> Full article ">Figure 10
<p>Linear absorption contrast comparison of vapor cells with different optical lengths at different temperatures.</p> Full article ">Figure 11
<p>Schematic of the coherent population trapping (CPT) measurement apparatus. External cavity diode laser (ECDL): DLCpro, Toptica (Farmington, NY, USA). BS: Beam splitter. POL: Linear polarizer. PD: Photodiode. Source 1: Precision current driver. Source 2: Voltage supplier. Source 3: Function generator. Microwave generator: Agilent E8257D PSG analog signal generator (Santa Clara, CA, USA). LIA: LI5640 lock-in amplifier (NF Corporation, Yokohama, Japan).</p> Full article ">Figure 12
<p>(<b>a</b>) Photo of the integrated physics package with polarization optics and the vapor cell; (<b>b</b>) Typical CPT 0-0 resonance error signal.</p> Full article ">Figure 13
<p>Measured (<b>a</b>) Full Width at Half Maximum (FWHM), height; (<b>b</b>) CPT signal contrast and FWHM/Contrast of the (0,0) CPT signal as a function of laser intensity for the microfabricated vapor cell.</p> Full article ">
13 pages, 49572 KiB  
Article
Comprehensive Die Shear Test of Silicon Packages Bonded by Thermocompression of Al Layers with Thin Sn Capping or Insertions
by Shiro Satoh, Hideyuki Fukushi, Masayoshi Esashi and Shuji Tanaka
Micromachines 2018, 9(4), 174; https://doi.org/10.3390/mi9040174 - 11 Apr 2018
Cited by 2 | Viewed by 5983
Abstract
Thermocompression bonding for wafer-level hermetic packaging was demonstrated at the lowest temperature of 370 to 390 °C ever reported using Al films with thin Sn capping or insertions as bonding layer. For shrinking the chip size of MEMS (micro electro mechanical systems), a [...] Read more.
Thermocompression bonding for wafer-level hermetic packaging was demonstrated at the lowest temperature of 370 to 390 °C ever reported using Al films with thin Sn capping or insertions as bonding layer. For shrinking the chip size of MEMS (micro electro mechanical systems), a smaller size of wafer-level packaging and MEMS–ASIC (application specific integrated circuit) integration are of great importance. Metal-based bonding under the temperature of CMOS (complementary metal-oxide-semiconductor) backend process is a key technology, and Al is one of the best candidates for bonding metal in terms of CMOS compatibility. In this study, after the thermocompression bonding of two substrates, the shear fracture strength of dies was measured by a bonding tester, and the shear-fractured surfaces were observed by SEM (scanning electron microscope), EDX (energy dispersive X-ray spectrometry), and a surface profiler to clarify where the shear fracture took place. We confirmed two kinds of fracture mode. One mode is Si bulk fracture mode, where the die shear strength is 41.6 to 209 MPa, proportionally depending on the area of Si fracture. The other mode is bonding interface fracture mode, where the die shear strength is 32.8 to 97.4 MPa. Regardless of the fracture modes, the minimum die shear strength is practical for wafer-level MEMS packaging. Full article
(This article belongs to the Special Issue Wafer Level Packaging of MEMS)
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<p>Cross-sectional structure of sample. (<b>a</b>) Ridge frame substrate; (<b>b</b>) Diaphragm substrate; (<b>c</b>) Al bonding layer inserted with thin Sn layers expressed as Al/Sn/Al/Sn/Al//Al/Sn/Al/Sn/Al; (<b>d</b>) Al bonding layer capped with thin Sn layer as Al/Sn//Sn/Al.</p> Full article ">Figure 1 Cont.
<p>Cross-sectional structure of sample. (<b>a</b>) Ridge frame substrate; (<b>b</b>) Diaphragm substrate; (<b>c</b>) Al bonding layer inserted with thin Sn layers expressed as Al/Sn/Al/Sn/Al//Al/Sn/Al/Sn/Al; (<b>d</b>) Al bonding layer capped with thin Sn layer as Al/Sn//Sn/Al.</p> Full article ">Figure 2
<p>Schematic of bonding tester setup for die shear fracture strength measurement.</p> Full article ">Figure 3
<p>An example of bonded substrate pairs. (<b>a</b>) Surface photograph at 22 h after bonding and distribution of sealed dies in the substrate; (<b>b</b>) Typical diaphragm deformation of sealed die measured by white light interferometer; (<b>c</b>) Sealed die after dicing.</p> Full article ">Figure 4
<p>Distribution of shear fracture strength for (<b>a</b>) non-hermetic dies and (<b>b</b>) hermetic dies. The bonding temperature and pressure, as well as the average of shear fracture strength are shown in each graph.</p> Full article ">Figure 5
<p>Shear fracture strength distributions for (<b>a</b>,<b>b</b>) Al/Sn//Sn/Al bonding layer structure and (<b>c</b>,<b>d</b>) Al/Sn/Al/Sn/Al//Al/Sn/Al/Sn/Al bonding layer structure. The upper graphs (<b>a</b>,<b>c</b>) show the total number of samples at each strength range regardless of bonding temperature. The lower graphs (<b>b</b>,<b>d</b>) show the number of samples for each bonding temperature at each strength range. The bonding temperature and pressure are shown in the graphs (<b>b</b>,<b>d</b>).</p> Full article ">Figure 6
<p>Results of EDX, SEM, and surface profile measurements of shear-fractured dies. (<b>a</b>) Surface photograph of ridge frame substrate; (<b>b</b>) Surface photograph of flat substrate; (<b>c</b>) SEM and EDX results of ridge frame substrate; (<b>d</b>) SEM and EDX results of flat substrate; (<b>e</b>) Surface profiles of separated substrates; (<b>f</b>) Schematic cross section of bonded area after fractured by shear force.</p> Full article ">Figure 7
<p>Results of EDX, SEM, and surface profile measurements of shear-fractured dies which showed shear fracture strength of 130 MPa. (<b>a</b>) Surface photograph of ridge frame substrate. (<b>b</b>) Surface photograph of flat substrate; (<b>c</b>) Surface photograph and EDX results of central right part of (<b>a</b>) and central left part of (<b>b</b>); (<b>d</b>) SEM and EDX results of ridge frame substrate; and (<b>e</b>) SEM and EDX results of flat substrate; (<b>f</b>) Surface profiles of shear-fractured positions R1 and F2; (<b>g</b>) Schematic cross section of shear-fractured positions R1 and F2.</p> Full article ">Figure 7 Cont.
<p>Results of EDX, SEM, and surface profile measurements of shear-fractured dies which showed shear fracture strength of 130 MPa. (<b>a</b>) Surface photograph of ridge frame substrate. (<b>b</b>) Surface photograph of flat substrate; (<b>c</b>) Surface photograph and EDX results of central right part of (<b>a</b>) and central left part of (<b>b</b>); (<b>d</b>) SEM and EDX results of ridge frame substrate; and (<b>e</b>) SEM and EDX results of flat substrate; (<b>f</b>) Surface profiles of shear-fractured positions R1 and F2; (<b>g</b>) Schematic cross section of shear-fractured positions R1 and F2.</p> Full article ">Figure 8
<p>Results of EDX, SEM, and surface profile measurements of shear-fractured die shown in <a href="#micromachines-09-00174-f007" class="html-fig">Figure 7</a>. (<b>a</b>) Surface photograph of bottom right part of <a href="#micromachines-09-00174-f007" class="html-fig">Figure 7</a>a and left part of <a href="#micromachines-09-00174-f007" class="html-fig">Figure 7</a>b. (<b>b</b>) SEM and EDX observation results of ridge frame substrate and (<b>c</b>) of flat substrate. (<b>d</b>) Surface profiles of positions R5 and F6; (<b>e</b>) Schematically depicted shear fracture cross section around position R5 and F6; (<b>f)</b> Surface profiles of positions R7 and F8; (<b>g)</b> Schematic cross section of shear-fractured positions R7 and F8.</p> Full article ">Figure 9
<p>Relationship between fractured Si frame ratio and shear fractured strength. Fractured Si frame ratio (%) is defined as black Si fracture length divided by bonding frame length. The linear approximation formula of region (A), and the bonding temperature and pressure are also represented.</p> Full article ">Figure 10
<p>FEM analysis of stress during die shear test. (<b>a</b>) Analysis model of sample shown in <a href="#micromachines-09-00174-f001" class="html-fig">Figure 1</a>; (<b>b</b>) Maximum principal stress in cross sections at positions A to D and “Corner” shown in (<b>a</b>).</p> Full article ">
13 pages, 16492 KiB  
Article
A Study on Measurement Variations in Resonant Characteristics of Electrostatically Actuated MEMS Resonators
by Faisal Iqbal and Byeungleul Lee
Micromachines 2018, 9(4), 173; https://doi.org/10.3390/mi9040173 - 9 Apr 2018
Cited by 10 | Viewed by 3793
Abstract
Microelectromechanical systems (MEMS) resonators require fast, accurate, and cost-effective testing for mass production. Among the different test methods, frequency domain analysis is one of the easiest and fastest. This paper presents the measurement uncertainties in electrostatically actuated MEMS resonators, using frequency domain analysis. [...] Read more.
Microelectromechanical systems (MEMS) resonators require fast, accurate, and cost-effective testing for mass production. Among the different test methods, frequency domain analysis is one of the easiest and fastest. This paper presents the measurement uncertainties in electrostatically actuated MEMS resonators, using frequency domain analysis. The influence of the applied driving force was studied to evaluate the measurement variations in resonant characteristics, such as the natural frequency and the quality factor of the resonator. To quantify the measurement results, measurement system analysis (MSA) was performed using the analysis of variance (ANOVA) method. The results demonstrate that the resonant frequency ( f r ) is mostly affected by systematic error. However, the quality (Q) factor strongly depends on the applied driving force. To reduce the measurement variations in Q factor, experiments were carried out to study the influence of DC and/or AC driving voltages on the resonator. The results reveal that measurement uncertainties in the quality factor were high for a small electrostatic force. Full article
(This article belongs to the Section A：Physics)
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<p>(<b>a</b>) Experimental setup for resonant characteristics measurement of the MEMS resonator. (<b>b</b>) Optical photograph of the vacuum packaged single structure 3-axis gyroscope. (<b>c</b>) Electrical model of the MEMS resonator.</p> Full article ">Figure 2
<p>Typical frequency response of a MEMS resonator.</p> Full article ">Figure 3
<p>Gage repeatability and reproducibility (R&amp;R) of (<b>a</b>) the resonant frequency <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <msub> <mi>f</mi> <mi>r</mi> </msub> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>b</b>) the quality (<math display="inline"> <semantics> <mrow> <mi mathvariant="normal">Q</mi> <mo stretchy="false">)</mo> <mtext> </mtext> <mi>factor</mi> </mrow> </semantics> </math> for condition 1.</p> Full article ">Figure 4
<p>Measurement variations in the Q factor from increasing the AC voltage.</p> Full article ">Figure 5
<p>Frequency response of a resonator from increasing the AC voltage at a fixed DC voltage of 1 V.</p> Full article ">Figure 6
<p>Measurement variations in the Q factor from increasing the DC voltage.</p> Full article ">Figure 7
<p>Frequency response of a resonator from increasing the DC voltage at a fixed AC voltage of 1 V<sub>pk</sub>.</p> Full article ">Figure 8
<p>Gage R&amp;R ANOVA results for (<b>a</b>) the resonant frequency <math display="inline"> <semantics> <mrow> <mrow> <mo>(</mo> <mrow> <msub> <mi>f</mi> <mi>r</mi> </msub> </mrow> <mo>)</mo> </mrow> <mo> </mo> </mrow> </semantics> </math> and (<b>b</b>) the Q factor for condition 2.</p> Full article ">Figure 9
<p>Frequency response function: (<b>a</b>) condition 1 and (<b>b</b>) condition 2.</p> Full article ">
9 pages, 14572 KiB  
Article
Millimeter-Wave Substrate Integrated Waveguide Using Micromachined Tungsten-Coated Through Glass Silicon Via Structures
by Ik-Jae Hyeon and Chang-Wook Baek
Micromachines 2018, 9(4), 172; https://doi.org/10.3390/mi9040172 - 9 Apr 2018
Cited by 10 | Viewed by 7828
Abstract
A millimeter-wave substrate integrated waveguide (SIW) has been demonstrated using micromachined tungsten-coated through glass silicon via (TGSV) structures. Two-step deep reactive ion etching (DRIE) of silicon vias and selective tungsten coating onto them using a shadow mask are combined with glass reflow techniques [...] Read more.
A millimeter-wave substrate integrated waveguide (SIW) has been demonstrated using micromachined tungsten-coated through glass silicon via (TGSV) structures. Two-step deep reactive ion etching (DRIE) of silicon vias and selective tungsten coating onto them using a shadow mask are combined with glass reflow techniques to realize a glass substrate with metal-coated TGSVs for millimeter-wave applications. The proposed metal-coated TGSV structures effectively replace the metallic vias in conventional through glass via (TGV) substrates, in which an additional individual glass machining process to form micro holes in the glass substrate as well as a time-consuming metal-filling process are required. This metal-coated TGSV substrate is applied to fabricate a SIW operating at Ka-band as a test vehicle. The fabricated SIW shows an average insertion loss of 0.69 ± 0.18 dB and a return loss better than 10 dB in a frequency range from 20 GHz to 45 GHz. Full article
(This article belongs to the Special Issue Wafer Level Packaging of MEMS)
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<p>Schematic view of the proposed substrate integrated waveguide (SIW) with tungsten-coated through glass silicon via (TGSV).</p> Full article ">Figure 2
<p>Simulated <span class="html-italic">S</span>-parameters of the SIWs with three different via structures: tungsten-coated low-resistive silicon, copper, and pure low-resistive silicon.</p> Full article ">Figure 3
<p>Fabrication process of the SIW with TGSVs.</p> Full article ">Figure 4
<p>(<b>a</b>) Photograph of the wafer after glass reflow and chemical mechanical polishing (CMP) processes; (<b>b</b>) Photograph of the fabricated SIW; (<b>c</b>) Magnified scanning electron microscope (SEM) image of the silicon via embedded in the glass substrate.</p> Full article ">Figure 5
<p>Simulated and measured <span class="html-italic">S</span>-parameters of the fabricated SIW.</p> Full article ">
12 pages, 36588 KiB  
Article
Spiral Microchannels with Trapezoidal Cross Section Fabricated by Femtosecond Laser Ablation in Glass for the Inertial Separation of Microparticles
by Ala’aldeen Al-Halhouli, Wisam Al-Faqheri, Baider Alhamarneh, Lars Hecht and Andreas Dietzel
Micromachines 2018, 9(4), 171; https://doi.org/10.3390/mi9040171 - 9 Apr 2018
Cited by 40 | Viewed by 9002
Abstract
The fabrication and testing of spiral microchannels with a trapezoidal cross section for the passive separation of microparticles is reported in this article. In contrast to previously reported fabrication methods, the fabrication of trapezoidal spiral channels in glass substrates using a femtosecond laser [...] Read more.
The fabrication and testing of spiral microchannels with a trapezoidal cross section for the passive separation of microparticles is reported in this article. In contrast to previously reported fabrication methods, the fabrication of trapezoidal spiral channels in glass substrates using a femtosecond laser is reported for the first time in this paper. Femtosecond laser ablation has been proposed as an accurate and fast prototyping method with the ability to create 3D features such as slanted-base channels. Moreover, the fabrication in borosilicate glass substrates can provide high optical transparency, thermal resistance, dimensional stability, and chemical inertness. Post-processing steps of the laser engraved glass substrate are also detailed in this paper including hydrogen fluoride (HF) dipping, chemical cleaning, surface activation, and thermal bonding. Optical 3D images of the fabricated chips confirmed a good fabrication accuracy and acceptable surface roughness. To evaluate the particle separation function of the microfluidic chip, 5 μm, 10 μm, and 15 μm particles were focused and recovered from the two outlets of the spiral channel. In conclusion, the new chemically inert separation chip can be utilized in biological or chemical processes where different sizes of cells or particles must be separated, i.e., red blood cells, circulating tumor cells, and technical particle suspensions. Full article
(This article belongs to the Special Issue Liquid Biopsy in a Microfluidic Chip for Rapid and Non-Invasive Point-of-Care Diagnostics)
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<p>Design of the spiral microfluidic chip and the final fabricated platform (<b>a</b>) illustration of the proposed trapezoidal spiral microfluidic channel design with one inlet and two outlets, larger and smaller radial increments as used for the laser ablation providing a sloped channel bottom are illustrated in the insert, (<b>b</b>) ready-made and bonded glass platform of the spiral channel, and (<b>c</b>) spiral microfluidic chip inside the aluminum holder for easier inlet/outlet tube connections.</p> Full article ">Figure 2
<p>Schematic illustration of the spiral operational concept with demonstration of Dean vortices and equilibrium position of different size particles (<b>top</b>) rectangular spiral channel with centered core of Dean vortices, (<b>bottom</b>) trapezoidal spiral channel with Dean vortices cores shifted towards the outer wall of the spiral channel, as a result, the equilibrium position of small particles is shifted for better separation efficiency.</p> Full article ">Figure 3
<p>Example illustrating the effect of the laser contouring process (<b>left</b>) microchannel without contouring, (<b>middle</b>) microchannel with contouring depth less than channel engraving depth (<b>right)</b> contouring with adequate number of repetitions (depth).</p> Full article ">Figure 4
<p>The fabricated spiral channel (<b>a</b>) 3D CLSM image of the fabricated channel with the roughness profile of the engraved area (<b>b</b>) 5000x SEM image of the fabricated channel showing the texture of the engraved, contouring, and wall areas of the channel.</p> Full article ">Figure 5
<p>Microparticles focusing paths vs. flow rate of fluid in the proposed trapezoidal spiral channel (dashed lines used to highlight microchannel walls).</p> Full article ">Figure 6
<p>(<b>a</b>) 3D green-plane intensity profile of experimentally focusing 5 μm particles when increasing flow rate from 0 to 5 mL·min<sup>−1</sup> over a period of around 8 s; (<b>b</b>) 5 μm and 15 μm particles separation using the proposed trapezoidal spiral channel (<b>top</b>) image captured with the inverted fluorescence microscope at 5 mL·min<sup>−1</sup> (<b>bottom</b>) green intensity profile shows the focusing peaks (each block on the <span class="html-italic">x</span>-axis is equal to 60 μm of the real channel width).</p> Full article ">
14 pages, 25715 KiB  
Article
Stretchable Tattoo-Like Heater with On-Site Temperature Feedback Control
by Andrew Stier, Eshan Halekote, Andrew Mark, Shutao Qiao, Shixuan Yang, Kenneth Diller and Nanshu Lu
Micromachines 2018, 9(4), 170; https://doi.org/10.3390/mi9040170 - 8 Apr 2018
Cited by 23 | Viewed by 8340
Abstract
Wearable tissue heaters can play many important roles in the medical field. They may be used for heat therapy, perioperative warming and controlled transdermal drug delivery, among other applications. State-of-the-art heaters are too bulky, rigid, or difficult to control to be able to [...] Read more.
Wearable tissue heaters can play many important roles in the medical field. They may be used for heat therapy, perioperative warming and controlled transdermal drug delivery, among other applications. State-of-the-art heaters are too bulky, rigid, or difficult to control to be able to maintain long-term wearability and safety. Recently, there has been progress in the development of stretchable heaters that may be attached directly to the skin surface, but they often use expensive materials or processes and take significant time to fabricate. Moreover, they lack continuously active, on-site, unobstructive temperature feedback control, which is critical for accommodating the dynamic temperatures required for most medical applications. We have developed, fabricated and tested a cost-effective, large area, ultra-thin and ultra-soft tattoo-like heater that has autonomous proportional-integral-derivative (PID) temperature control. The device comprises a stretchable aluminum heater and a stretchable gold resistance temperature detector (RTD) on a soft medical tape as fabricated using the cost and time effective “cut-and-paste” method. It can be noninvasively laminated onto human skin and can follow skin deformation during flexure without imposing any constraint. We demonstrate the device’s ability to maintain a target temperature typical of medical uses over extended durations of time and to accurately adjust to a new set point in process. The cost of the device is low enough to justify disposable use. Full article
(This article belongs to the Special Issue Flexible Electronics: Fabrication and Ubiquitous Integration)
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Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) Fabrication process used for heater and resistance temperature detector (RTD), shown for heater. Material is put on the thermal release tape (TRT) and cut with Silhouette cutter. TRT is heated, excess material is removed and remaining material is transferred to Tegaderm; (<b>b</b>) Complete device on tegaderm. Aluminum with blue polyimide backing forms the resistive heating element while Au/Cr 100/10 nm forms the resistance temperature detector.</p> Full article ">Figure 2
<p>(<b>a</b>,<b>b</b>) Device conforms to hand and maintains its conformability during opening and closing; (<b>c</b>,<b>d</b>) Infrared (IR) images of the device powered with proportional-integral-derivative (PID) control as the hand is opened and closed. The PID controller automatically adjusts power output so the hand does not overheat when it closes.</p> Full article ">Figure 3
<p>(<b>a</b>) Circuit diagram of set-up for calibration of RTD in situ. Heater is brought to different temperatures by adjusting Vin. Resistance and temperature are measured simultaneously using a digital multimeter (DMM) and IR camera, respectively; (<b>b</b>) Lateral heat distribution of heater. Blue, red and green lines on IR image mark the horizontal line across which temperature was measured for their respective red, blue and green plots. Temperature distribution is fairly uniform. Dotted purple line on IR image shows area that the IR camera calculated the average temperature for; (<b>c</b>) Average temperature of area marked by the dotted purple line in <a href="#micromachines-09-00170-f003" class="html-fig">Figure 3</a>b (top) and resistance of Au/Cr RTD as measured by DMM (bottom) each plotted across time as Vin was changed to 3.8 V, 4.5 V and finally 5.1 V; (<b>d</b>) The calibration curve for the RTD: ΔR/R<sub>0</sub> of the RTD versus ΔT of the average temperature of the area around the RTD as marked by the dotted purple line in <a href="#micromachines-09-00170-f003" class="html-fig">Figure 3</a>b. The calibration constant, β, is marked and is equal to 0.000203.</p> Full article ">Figure 4
<p>(<b>a</b>) COMSOL thermal simulation results (left: top view; right: 3D view); (<b>b</b>) Lateral heat distribution of heater. Blue, red and green lines on simulation image (left) mark the horizontal line across which temperature was collected for their respective red, blue and green plots; (<b>c</b>) Vertical heat distribution of skin from the black line on simulation image (right).</p> Full article ">Figure 5
<p>(<b>a</b>) Circuit diagram of set up for operating heater with PID control. DMM measures resistance of RTD and feeds it into a computer with LabVIEW, The LabVIEW program calculates the temperature of the RTD using the RTD’s starting temperature, starting resistance and calibration constant. It then uses a PID algorithm to calculate the optimal duty cycle for PWM of the heater given the heater’s current temperature and the set point temperature for the heater. The LabVIEW program then uses the data acquisition unit (DAQ) to switch the relay on and off with the determined duty cycle, thus controlling how much total power is fed to the heater; (<b>b</b>) Temperature of the heater versus time measured with both the RTD and the IR camera as the heater is turned on at a set point of 38.5 °C and then turned off. Heater is able to maintain set point temperature for an extended period of time; (<b>c</b>) Temperature of the heater versus time measured with both the RTD and the IR camera as the set point of the heater is changed while the voltage remains constant. At 40 °C, 6.2 V is not sufficient for the heater to reach the set point, so the voltage is increased to 7 V, at which point the heater is able to reach and maintain a temperature of 40 °C.</p> Full article ">Figure 6
<p>(<b>a</b>) Plot of heater temperature versus time as the set points and voltages are changed, followed by a plot of the corresponding duty cycle versus time. The average of the steady state duty cycles marked 1, 2 and 3 were used to calculate the power densities plotted below marked 1, 2 and 3, respectively, at different temperatures; (<b>b</b>) The same plots as figure A except the heater is insulated with a piece of foam.</p> Full article ">
9 pages, 12547 KiB  
Article
Effect of Substrate Support on Dynamic Graphene/Metal Electrical Contacts
by Jihyung Lee, Xiaoli Hu, Andrey A. Voevodin, Ashlie Martini and Diana Berman
Micromachines 2018, 9(4), 169; https://doi.org/10.3390/mi9040169 - 7 Apr 2018
Cited by 12 | Viewed by 4850
Abstract
Recent advances in graphene and other two-dimensional (2D) material synthesis and characterization have led to their use in emerging technologies, including flexible electronics. However, a major challenge is electrical contact stability, especially under mechanical straining or dynamic loading, which can be important for [...] Read more.
Recent advances in graphene and other two-dimensional (2D) material synthesis and characterization have led to their use in emerging technologies, including flexible electronics. However, a major challenge is electrical contact stability, especially under mechanical straining or dynamic loading, which can be important for 2D material use in microelectromechanical systems. In this letter, we investigate the stability of dynamic electrical contacts at a graphene/metal interface using atomic force microscopy (AFM), under static conditions with variable normal loads and under sliding conditions with variable speeds. Our results demonstrate that contact resistance depends on the nature of the graphene support, specifically whether the graphene is free-standing or supported by a substrate, as well as on the contact load and sliding velocity. The results of the dynamic AFM experiments are corroborated by simulations, which show that the presence of a stiff substrate, increased load, and reduced sliding velocity lead to a more stable low-resistance contact. Full article
(This article belongs to the Special Issue Carbon Based Materials for MEMS/NEMS)
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<p>Summary of the experimental setup. (<b>a</b>) Schematic of the AFM measurements of electrical contact evolution for Pt/Ir tip and graphene performed for free-standing and supported graphene and (<b>b</b>) photograph of the sample assembly. (<b>c</b>) Metal–graphene band diagram for the contact. (<b>d</b>) SEM image of the conductive AFM tip. (<b>e</b>) SEM image of the single layer graphene transferred on a silicon nitride substrate with holes. (<b>f</b>) Raman analysis confirming single layer graphene presence after the graphene transfer.</p> Full article ">Figure 2
<p>I–V characteristics of (<b>a</b>) supported graphene and (<b>b</b>) free-standing graphene as a function of the applied load. In the case of the supported graphene, larger current is observed at the lower loads. The 2.7 nN steps were selected to provide a uniform distribution of applied loads. (<b>c</b>) Height profile scan indicates (<b>d</b>) ~40 nm sagging of graphene in the free-standing area resulting from the transfer procedure.</p> Full article ">Figure 3
<p>Conductive measurements during scanning of the graphene sample. Detailed 100 nm scans of the supported graphene area at scan speeds of (<b>a</b>) 50 nm/s and (<b>b</b>) 100 nm/s show that current was higher at the slower scan speed. In the case of free-standing graphene, overall conductivity is substantially lower both for (<b>c</b>) slow scanning and (<b>d</b>) faster scanning than for the supported graphene. In the case of the free-standing graphene, current is substantially reduced to ~0.2 μA at a scanning velocity of 50 nm/s and to 0.01–0.02 μA at 100 nm/s. The applied load was 5.4 nN for all results shown. The color scale bars cover the range from 0 up to 1.2 μA.</p> Full article ">Figure 4
<p>Snapshots of the models of (<b>a</b>) free-standing graphene and (<b>b</b>) supported graphene, where the main figures show perspective views of half of the model systems and the insets show bottom views. The regions identified by the dashed box in the insets correspond to those shown in the perspective views. (<b>c</b>) The interaction force between the tip and substrate as a function of relaxation time for free-standing graphene and supported graphene, where the dashed red line shows the average interaction force for both models. The insets show representative snapshots of the tip and free-standing graphene layer when they are in (bottom inset) and out of (top inset) contact.</p> Full article ">
21 pages, 13091 KiB  
Article
Analytical Model and Experimental Evaluation of the Micro-Scale Thermal Property Sensor for Single-Sided Measurement
by Takashi Katayama, Kaoru Uesugi and Keisuke Morishima
Micromachines 2018, 9(4), 168; https://doi.org/10.3390/mi9040168 - 5 Apr 2018
Cited by 4 | Viewed by 4475
Abstract
We report a new analytical model of the MEMS-based thermal property sensor for samples which are difficult to handle and susceptible to damage by thermal stimulus, such as living cells. Many sensor designs had been reported for thermal property measurements, but only a [...] Read more.
We report a new analytical model of the MEMS-based thermal property sensor for samples which are difficult to handle and susceptible to damage by thermal stimulus, such as living cells. Many sensor designs had been reported for thermal property measurements, but only a few of them have considered the analytical model of the single-sided measurement in which a measurement sample is placed on the sensor substrate. Even in the few designs that have considered the analytical model, their applicable limits are restricted to more than 1 mm length in practical situations. Our new model considers both the sample and the sensor substrate thermal properties and is applicable to a sensor length less than 1 µm. In order to minimize the influence of the heat stimulus to the sample, the model formulates the required heat dissipating time for different sensor geometries. We propose fast and precise detection circuit architecture to realize our model, and we discuss the sensor performance for a number of different designs. Full article
(This article belongs to the Special Issue State-of-the-Art Lab-on-a-Chip Technology in Japan)
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<p>Model for the B.M.W. solution. <math display="inline"> <semantics> <mrow> <mi>T</mi> </mrow> </semantics> </math> (unit: K), temperature; <math display="inline"> <semantics> <mrow> <mi>ρ</mi> </mrow> </semantics> </math> (unit: kg/m<sup>3</sup>), density; <math display="inline"> <semantics> <mrow> <mi>C</mi> <mi>p</mi> </mrow> </semantics> </math> (unit: J/(kg × K)), specific heat capacity; <math display="inline"> <semantics> <mrow> <mi>k</mi> </mrow> </semantics> </math> (unit: W/(m × K)), thermal conductivity; <math display="inline"> <semantics> <mrow> <mi>α</mi> </mrow> </semantics> </math> (unit: m<sup>2</sup>/s), thermal diffusivity; <math display="inline"> <semantics> <mrow> <msup> <mi>z</mi> <mo>′</mo> </msup> <mo>&gt;</mo> <mn>0</mn> </mrow> </semantics> </math>, position of the point heat source. The subscript designates its domain.</p> Full article ">Figure 2
<p>Model for the rectangle heat source on the interface of two semi-infinite domains.</p> Full article ">Figure 3
<p>Comparison of the relative approximation error with various approximation functions.</p> Full article ">Figure 4
<p>Temperature-decreasing ratio of the different heat source geometries, point, line, and plane.</p> Full article ">Figure 5
<p>Temperature-decreasing ratio of the point heat source immediately after the end of heating.</p> Full article ">Figure 6
<p>Temperature-decreasing ratio of the strip heat source.</p> Full article ">Figure 7
<p>Temperature-decreasing ratio of the rectangle heat source.</p> Full article ">Figure 8
<p>Design of the sensor device: (<b>a</b>) Overview and (<b>b</b>) nickel patterns for the 2-terminal-type (left) and 4-terminal-type (right).</p> Full article ">Figure 9
<p>Photograph of the rectangle pattern on the sensor. The design was 2 µm wide and 50 µm long.</p> Full article ">Figure 10
<p>Wiring connection to the device terminal.</p> Full article ">Figure 11
<p>Schematic of the circuit diagram.</p> Full article ">Figure 12
<p>Timing chart of the detection circuit.</p> Full article ">Figure 13
<p>Schematic of the setup of the sensor device.</p> Full article ">Figure 14
<p>Estimation results of the long-term stability of the detection circuit: (<b>a</b>) 5 days; (<b>b</b>) 24 h.</p> Full article ">Figure 15
<p>Estimated electrical resistivity as functions of the width of the rectangle pattern.</p> Full article ">Figure 16
<p>Example of the analytical value during the TCR evaluation (<b>a</b>) 1 cycle; (<b>b</b>) 30 °C setting period.</p> Full article ">Figure 17
<p>Example of the analytical value during the detection performance evaluation.</p> Full article ">Figure 18
<p>Comparison of the detection index for different rectangle areas.</p> Full article ">
8 pages, 9700 KiB  
Article
A Visualization Technique of a Unique pH Distribution around an Ion Depletion Zone in a Microchannel by Using a Dual-Excitation Ratiometric Method
by Katsuo Mogi
Micromachines 2018, 9(4), 167; https://doi.org/10.3390/mi9040167 - 2 Apr 2018
Cited by 7 | Viewed by 4392
Abstract
The ion depletion zone of ion concentration polarization has a strong potential to act as an immaterial barrier, separating delicate submicron substances, including biomolecules, without causing physical damage. However, the detailed mechanisms of the barrier effect remain incompletely understood because it is difficult [...] Read more.
The ion depletion zone of ion concentration polarization has a strong potential to act as an immaterial barrier, separating delicate submicron substances, including biomolecules, without causing physical damage. However, the detailed mechanisms of the barrier effect remain incompletely understood because it is difficult to visualize the linked behavior of protons, cations, anions, and charged molecules in the thin ion depletion zone. In this study, pH distribution in an ion depletion zone was measured to estimate the role of proton behavior. This was done in order to use it as a tool with good controllability for biomolecule handling in the future. As a result, a unique pH peak was observed at several micrometers distance from the microchannel wall. The position of the peak appeared to be in agreement with the boundary of the ion depletion zone. From this agreement, it is expected that the pH peak has a causal connection to the barrier effect of the ion depletion zone. Full article
(This article belongs to the Special Issue Selected Papers from the 8th Symposium on Micro-Nano Science and Technology on Micromachines)
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<p>Schematic of microchannels for ion concentration polarization (ICP). The left schematic is a top view of a region composed of two microchannels and a cation-exchange membrane. The right schematic is a cross-sectional view of A-A’ in the left schematic. Generating a difference in potential causes the movement of cations through the membrane, whereas anions remain in their original channels. Under steady-state ICP, an ion depletion zone is formed around the high-potential side of the membrane.</p> Full article ">Figure 2
<p>Schematic of the experimental system. (<b>a</b>) Microfluidic device for ICP made of glass and substrates; (<b>b</b>) A schematic of the microscopic system used for pH measurement. Excitation beams at 458 nm and 488 nm were used in a dual-excitation ratiometric method. The microfluidic device on the microscopic system was connected to a syringe pump and a voltage supply.</p> Full article ">Figure 3
<p>Schematic of the fabrication process for Nafion patterning. (<b>a</b>) Cross-sectional view of Nafion patterned on a glass substrate using a polydimethylsiloxane (PDMS) mold; (<b>b</b>) Nafion pattern cured at 100 °C for 10 min after peeling off the mold; (<b>c</b>) Assembly of the PDMS substrate onto the glass substrate; (<b>d</b>) Completed microfluidic ICP device.</p> Full article ">Figure 4
<p>Calibration curve between pH value and fluorescein isothiocyanate (FITC) intensity. (<b>a</b>) FITC intensities of pH standard solutions obtained by dual excitation at 458 nm and 488 nm. Each intensity shown is the mean value over a 28 × 28 µm<sup>2</sup> square, and the error bar shows the standard deviation; (<b>b</b>) A calibration curve between pH value and the quotient of the intensities, normalized by the maximum value. The calibration curve is a polynomial approximation: <math display="inline"> <semantics> <mrow> <mi>y</mi> <mo>=</mo> <mn>58.2</mn> <msup> <mi>x</mi> <mn>5</mn> </msup> <mo>−</mo> <mn>151.3</mn> <msup> <mi>x</mi> <mn>4</mn> </msup> <mo>+</mo> <mn>148.7</mn> <msup> <mi>x</mi> <mn>3</mn> </msup> <mo>−</mo> <mn>72.3</mn> <msup> <mi>x</mi> <mn>2</mn> </msup> <mo>+</mo> <mn>23.1</mn> <mi>x</mi> <mo>+</mo> <mn>0.8</mn> </mrow> </semantics> </math>. The R-squared value was 1.0 from a pH of 2.68 to a pH of 7.28, excluding the endpoints of 2.05 and 8.18.</p> Full article ">Figure 5
<p>Measurement area and the FITC intensity distribution. (<b>a</b>) Photo of fluorescent intensity of FITC in steady state at the ion depletion zone in the microchannel. The zero position of the <span class="html-italic">x</span>-axis is the wall surface of the main channel, and the zero position of the <span class="html-italic">y</span>-axis is the center of the Nafion pattern. Lines a, b and c are parallel to the <span class="html-italic">x</span>-axis, and their positions on the <span class="html-italic">y</span>-axis are <span class="html-italic">y</span> = 139 µm, 0 µm and −139 µm; (<b>b</b>) Intensity distributions obtained by dual excitation at 458 nm and 488 nm under a steady-state ion depletion zone at lines a, b and c.</p> Full article ">Figure 6
<p>FITC concentration distribution and pH distribution at the ion depletion zone generated by ICP. (<b>a</b>) FITC concentration distributions under steady state at lines a, b and c while applying ICP, with ICP and without ICP. The dotted line at <span class="html-italic">x</span> = 9.0 ± 0.10 µm is the boundary of the ion depletion zone; (<b>b</b>) pH distribution obtained from the intensity quotient values after excitation at 458 nm and 488 nm (“I488/I458”), with ICP and without ICP. The pH distribution with ICP has a convex peak at <span class="html-italic">x</span> = 6.3 ± 0.15 µm and a concave peak at <span class="html-italic">x</span> = 9.1 ± 0.08 µm; (<b>c</b>) FITC concentration and pH distributions at lines a, b, and c under steady-state ICP.</p> Full article ">
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