Printed Electronics

Wireless biosensor applications require RF electronics to operate in immediate proximity of the body. This work investigates the effect of human body on RF circuits by simulations and measurements. Design methodology and initial design guidelines for body-worn discrete RF electronics are presented. The test structures are manufactured using printed electronics technology well suited for thin, flexible body-worn wireless sensor applications. The results indicate that in direct contact the human body significantly affects the performance of an RF circuit and needs to be considered. The research is relevant for modeling-based design of flexible body-worn wireless sensors.

Early demonstrations of wearable devices have driven interest in flexible lithium-ion batteries. Previous demonstrations of flexible lithium-ion batteries trade off between low areal capacity, poor mechanical flexibility and/or high thickness of inactive components. Here, a reinforced electrode design is used to support the active layers of the battery and a freestanding carbon nanotube (CNT) layer is used as the current collector. The supported architecture helps to increase the areal capacity (mAh cm-2) of the battery and improve the tensile strength and mechanical flexibility of the electrodes. Batteries based on lithium cobalt oxide and lithium titanate oxide shows excellent electrochemical and mechanical performance. The battery has an areal capacity of ≈1 mAh cm-2 and a capacity retention of around 94% after cycling the battery for 450 cycles at a C/2 rate. The reinforced electrode has a tensile strength of ≈5.5–7.0 MPa and shows excellent capacity retention after repeatedly flexing to a bending radius ranging from 45 to 10 mm. The relationships between mechanical flexing, electrochemical performance, and mechanical integrity of the battery are studied using electrochemical cycling, electron microscopy, and electrochemical impedance spectroscopy (EIS).

Advances in wireless technologies, low-power electronics, the internet of things, and in the domain of connected health are driving innovations in wearable medical devices at a tremendous pace. Wearable sensor systems composed of flexible and stretchable materials have the potential to better interface to the human skin, whereas silicon-based electronics are extremely efficient in sensor data processing and transmission. Therefore, flexible and stretchable sensors combined with low-power silicon-based electronics are a viable and efficient approach for medical monitoring. Flexible medical devices designed for monitoring human vital signs, such as body temperature, heart rate, respiration rate, blood pressure, pulse oxygenation, and blood glucose have applications in both fitness monitoring and medical diagnostics. As a review of the latest development in flexible and wearable human vitals sensors, the essential components required for vitals sensors are outlined and discussed here, including the reported sensor systems, sensing mechanisms, sensor fabrication, power, and data processing requirements.

Traditional printing methods offer the advantage of well-matured technology, high accuracy of depositing inks over flexible substrates at high web speeds, and low cost of fabrication. The components of a battery—the current collectors, active layers, and separator—can all be deposited using convention- al printing techniques by designing suitable inks. A combination of low thickness of printed electrodes, flexible packaging, battery architecture, and material properties makes printed batteries flexible. In this paper, we will discuss mate- rial challenges and mechanical limits of flexible printed batteries. We will review several printing techniques and present examples of batteries printed using these methods. In addition, we will briefly discuss other novel non-printed compliant batteries that have unique mechanical form.

Flexible lithium ion batteries are necessary for powering next generation of wearable electronic devices. In most designs, the mechanical flexibility of the battery is improved by reducing the thickness of the active layers, which in turn reduces the areal capacity and energy density of the battery. The performance of a battery depends on the electrode composition, and in most flexible batteries, standard electrode formulation is used, which is not suitable for flexing. Even with considerable efforts towards the development of flexible lithium ion batteries, the formulation of the electrodes has received very little attention. In this study, we investigate the relation between the electrode formulation and the mechanical strength of the electrodes. Peel and drag test are used to compare the adhesion and cohesion strength of the electrodes. The strength of an electrode is sensitive to the particle size and the choice of polymeric binder. By optimizing the electrode composition, we are able to fabricate a high areal capacity (~2mAh/cm2), flexible lithium ion battery with conventional metal-based current collectors that show superior electrochemical and mechanical performance in comparison to batteries with standard composition.

Nanoparticulate printed silver is a core material to flexible, printed circuits. Some commercial silvers are of a sufficient purity that
one may consider their use in electrochemical power sources and sensors. We establish an iterative rapid prototyping and
measuring method, printing electrodes, annealing them under temperature conditions from 210 to 280°C, and cycling them in a
microfluidic cell such that the electrolyte becomes the shearing medium. Electrode strength is quantified by the breakage due to
generation of gas-phase oxygen at the electrode. This oxygen generation assisted breaking is found to be a function of the amount
of oxygen generation only, independent of current density and electrolyte flow rate. Silver cured at 280°C for 60 min had highest
strength and required an average of 241.8 mC/mm2
at electrode rupture; curing at 280°C for 20 min required only 203.8 mC/mm2
for failure. Silver strength is quantified as an oxidant storage medium in the forms Ag2O and AgO and as a printed reference
electrode. Ag and AgO have higher shear strength compared to Ag2O. Thus, shear strength of silver oxide electrodes at potentials
of 0.15–0.55 V against a printed silver reference depends on the oxidation stat

We describe the use of omniphobic “fluoroalkylated paper” (“R F paper”) as a substrate for inkjet printing of aqueous inks that
are the precursors of electrically conductive patterns. By controlling the surface chemistry of the paper, it is possible to print high resolution, conductive patterns that remain conductive after folding and exposure to common solvents. Inkjet printing on omniphobic paper is a promising method of fabrication for low-cost, fl exible, foldable, and disposable conductors on paper (and other fl exible substrates) for electronics, microelectromechanical systems (MEMS), displays, and other applications. The ability to resist wetting by liquids with a wide range of surface tensions, combined with foldability, mechanical flexibility, light weight, low cost, and gas permeability, makes omniphobic R F paper a versatile alternative to the polymer, glass and silicon based materials upon which printed electronics are currently being deposited.

In the present review the state-of-the art and trends in the design and elaboration of fully inkjet printed sensors for abiotic environmental factors are summarized. The study is focused to technological aspect of sensor fabrication such as used printer, inks and substrates. The paper reviews five sensor types for temperature, humidity, pressure, irradiance and chemical properties measurement based on different transduction principles.

pi-Conjugated molecular materials with fused rings are the focus of considerable interest in the emerging area of organic electronics, since the combination of excellent charge carrier mobility and high stability may lead to their practical applications. This tutorial review discusses the synthesis, properties and applications of pi-conjugated organic semiconducting materials, especially those with fused rings. The achievements to date, the remaining problems and challenges, and the key research that needs to be done in the near future are all discussed.

An optimized, formulated polyurethane (PU)-based insulating ink, which was inkjet printed and cured as a tri-layer on top of an inkjet-printed and sintered commercial silver ink base metal fused to polyethylene terephthalate substrate, demonstrated a resistivity of >1.2 9 10 8 X cm at a film thickness of 100 lm when exposed to an aqueous saline solution and a voltage differential of <2 V. This insulating property is highly desirable for biofluids-contacting biosensors. Three PU-based insulator ink formulations were made with different levels of ethylene glycol and carboxymethylcellulose additives to improve ink volatility, viscosity, and dispersion properties. Based on the resultant ink properties important to printing, one of these formulations was selected for further evaluation. The effects of the type and extent of surface conditioning involving UV–O 3 and/or thermal treatments on print quality and completed insulator functionality are discussed. Print quality is assessed by visual and profilometry measurement.

This paper presents an investigation about the ideal composition of cell libraries to be used for digital Application Specific Printed Electronics Circuits (ASPECs). Printed/organic/flexible electronics is becoming more and more important over the last years, and it seems that the industry will continue growing as new possible applications arise, and the existing ones are being improved due to better designs and fabrication processes. This paper presents considerations for developing (ASPECs), trying to keep a similar approach to the typical ASIC procedures. The work presented herein adopted a cell-based design methodology addressed to printed electronics designs. Such methodology allows us to consider a design flow for printed electronics similar to the VLSI design flow, comprising logic synthesis, mapping, placement, and routing. In order to evaluate different library compositions, a set of benchmark has been mapped with six different combinations of mapping tools and associated libraries. The obtained results show that a simple library composed of just three cells – either NAND2, NOR2 and inverters or NAND, NAND3 and inverters – performs pretty well in terms of transistor count. Using a more complex cell library can produce reductions of around 25% in terms of transistor count, but produce increases of around 23% as well.

— The advent of the Internet has resulted in many new opportunities for creating and delivering content in digital form. Applications where digital watermarking is used are copyright protection, source tracking (different recipients get differently watermarked content), broadcast monitoring (television news often contains watermarked video from international agencies), video authentication and web publishing. An important issue that arises in these applications is protection of the rights of document owners. It has been recognized for quite some time that current copyright laws are inadequate for dealing with digital data. This has led to an interest in developing new copy deterrence and protective mechanisms. Digital watermarking is the process of embedding information into digital multimedia content such that the information (which we call the watermark) can later be extracted or detected for a variety of purposes, including copy prevention and control. We will be using LSBs of Blue components to rearrange the data in the original image so that it will give us very less distortion in the range of 0.00001 percent, which is not detectable by the human naked eyes. And thus we will embed our watermark information. We are making use of blue component of pixel as it has the LSB of the value and changing the LSB will affect the least to the value.

Bioelectronic interfaces require electrodes that are mechanically flexible and chemically inert. Flexibility allows pristine electrode contact to skin and tissue, and chemical inertness prevents electrodes from reacting with biological fluids and living tissues. Therefore, flexible gold electrodes are ideal for bioimpedance and biopotential measurements such as bioimpedance tomography, electrocardiography (ECG), electroencephalography (EEG), and electromyography (EMG). However, a manufacturing process to fabricate gold electrode arrays on plastic substrates is still elusive. In this work, a fabrication and low-temperature sintering (≈200 °C) technique is demonstrated to fabricate gold electrodes. At low-temperature sintering conditions, lines of different widths demonstrate different sintering speeds. Therefore, the sintering condition is targeted toward the widest feature in the design layout. Manufactured electrodes show minimum feature size of 62 μm and conductivity values of 5 × 10 6 S m−1. Utilizing the versatility of printing and plastic electronic processes, electrode arrays consisting of 31 electrodes with electrode-to-electrode spacing ranging from 2 to 7 mm are fabricated and used for impedance mapping of conformal surfaces at 15 kHz. Overall, the fabrication process of an inkjet-printed gold electrode array that is electrically reproducible, mechanically robust, and promising for bioimpedance and biopotential measurements is demonstrated.

The use of fibre-based materials as substrates in printed electronics has been increasing, mainly due to its attractive characteristics, such as low-cost or wide availability. Additionally, paper enables recycling and it shows attractive features, such as high thermal stability, when compared to traditional polymer-based substrates (Tobjörk and Österbacka, 2011 [1]). Nevertheless, one of the drawbacks of using paper substrates is that the surface usually is very rough, typically, showing roughness values above 10 μm2. In most cases, printing structures that need to be highly uniform, without disruptions, require additional coating. Inkjet printing provides sharp detail reproduction and strict lines on printed structures. Sintering is required for drying the ink. Thermal sintering is the traditionally used method, but requires long periods of time and promotes the ageing of the paper due to a long exposure at high temperature. When printing conductive structures on paper alternative photonic sintering methods such as IR-sintering show some attractive characteristics. IR-sintering is compatible with roll-to-roll fabrication, providing low-cost, fast and localized sintering, which makes it suitable for fibre-based substrates (Tobjörk et al., 2012 [3]). This work has been carried out to study and compare the efficiency of thermal and IR sintering of conductive structures on different paper and polymer substrates. All substrates were printed using silver based ink, which was applied on the substrate surface by inkjet. Resistivity values of the printed structures were used to compare the performance on the substrates. IR-sintering showed the best results in terms of achieved conductivity of the printed lines when using short sintering time of no more than 10 min. The conductivity values of the inkjet-printed silver lines on Lumi silk substrate reached about 40% of the bulk silver value after IR-sintering, whereas with thermal-sintering this value only reached about 20% of the bulk silver value. IR-sintering improves the sintering process, increasing the conductivity of the printed structures and at the same time reducing significantly the sintering time. In the case of Lumi silk substrate, high conductivity was observed after only two minutes of sintering time when IR-oven was used.

Both techniques can be used in a roll-to-roll mass manufacturing process, enabling the fabrication in large scale of flexible electronic devices, on paper substrates, without the need for extra steps, such as coatings.

When pressure is applied to a localized area of the body for an extended time, the resulting
loss of blood flow and subsequent reperfusion to the tissue causes cell death and a pressure
ulcer develops. Preventing pressure ulcers is challenging because the combination of pressure
and time that results in tissue damage varies widely between patients, and the underlying
damage is often severe by the time a surface wound becomes visible. Currently, no method
exists to detect early tissue damage and enable intervention. Here we demonstrate a flexible,
electronic device that non-invasively maps pressure-induced tissue damage, even when such
damage cannot be visually observed. Using impedance spectroscopy across flexible electrode
arrays in vivo on a rat model, we find that impedance is robustly correlated with tissue health
across multiple animals and wound types. Our results demonstrate the feasibility of an
automated, non-invasive ‘smart bandage’ for early detection of pressure ulcers.

The printing of functional inks on paper offers the possibility of light weight, thin film electronic devices that increase the value of the product and reduce the overall cost of device implementation. One application for such technology is the printing of radio frequency identification (RFID) tags directly to packaging materials. As the functionality of paper increases, an understanding of the base paper and coating layer contributions to the electrical performance of the printed device becomes increasingly important. In this project, the influence of coating components on the electrical resistivity of a commercially available SBS board was examined. Different coatings were applied to understand the contribution of selected pigments and binders on the electrical resistivity of the chosen substrate. A Keithley 6517A high resistance meter was used to measure the electrical resistivity of the substrates.

Silver nanoparticles (AgNP) are being used extensively in medical and modern age stretchable and flexible electronics applications. In this article, we describe easy, cost-effective, and scalable synthesis of AgNP using electrolysis of pure silver metal in aqueous silver acetate solution. Size measurements and structural characterizations of the nanoparticles were performed using scanning electron microscopy coupled with image analysis and X-ray diffraction techniques, respectively. As-prepared nanoparticles were dispersed in pure ethylene glycol (EG) in a concentration of 50 wt%. The dispersion was coated on a soft, sticky, stretchable, and flexible elastomeric substrate polydimethylsiloxane (PDMS). Finally, the stretchability and flexibility tests on AgNP-EG/PDMS laminate were performed. The as-fabricated AgNP-EG/PDMS laminate is capable of stretching up to 18% without electrical failure. It was also found to remain electrically conductive when bent on curved surfaces. This behavi...

The objective of this work was to design and fabricate a low cost resonant capacitive acoustic sensor using printing techniques. It falls within the frame of a collaborative research project named “Spinnaker”, set up by TAGSYS RFID, a French company, which has planned to integrate this sensor to improve the geolocalization of their RFID tags. This work started with the design and optimization of the sensor using finite element modeling (COMSOL) and design of experiments (DOE). This first step has enabled the identification of the optimum set of parameters and demonstrated that the output responses were in accordance with the specifications. Then, we have developed the different technological building blocks required for the fabrication of the prototypes using jointly the 2D inkjet printing technique and 3D printing method. The functionality of the sensors has been characterized using both capacitive and acoustic measurements using laser Doppler vibrometer. Experimental results showe...

A 20 × 20 pixel pressure sensor array based on a printed active-matrix single-wall carbon-nanotube thin-film transistor backplane is presented. Using a gravure printing process that is compatible with fully printed large area roll-to-roll processing, a 97% device yield is obtained on the 400-transistor backplane. As proof of concept, pressure sensors are integrated to map the applied tactile pressure across the array.

Recent years have witnessed significant research efforts in flexible organic and amorphous-metal-oxide analogue electronics, in view of its formidable potential for applications such as smart-sensor systems. This book provides a comprehensive overview of this growing research area. After discussing the properties of organic and amorphous-metal-oxide technologies relevant to analogue circuits, this book focuses on their application to two key circuit blocks: amplifiers and analogue-to-digital converters. The book thus provides a fresh look at the evolution and immediate opportunities of the field, and identifies the remaining challenges for these technologies to become the platform of choice for flexible analogue electronics.

The monitoring of pH values of liquids for environmental, industrial, and biological applications requires sensitive, stable, compact, and easy-to-use pH sensors. Here, we develop an inkjet printing process to deposit functionalized single-wall carbon nanotubes as both electron conduction and pH sensitive layers. Doping and de-doping of the carbon nanotubes by hydronium and hydroxide ions is the primary pH sensing mechanism. Multi-pass printing is used to deposit closely packed thin films and reduce the electrode resistance for efficient electron conduction and improved pH sensitivity. The printed electrodes on glass substrates show a reproducible pH sensitivity of 48.1 mV/pH with an average response time of 7 s and a small hysteresis of 4 mV. In addition, similar pH sensing behaviors are obtained by carbon nanotubes printed on flexible polymeric substrates. The developed inkjet printing process and pH sensing electrodes provide a cost-effective solution for future electrochemical monitoring systems.