Integrated 3D Hydrogel Waveguide Out-Coupler by Step-and-Repeat Thermal Nanoimprint Lithography: A Promising Sensor Device for Water and pH
<p>Schematic of the process flow for the 3D silicon master stamp fabrication. (<b>a</b>) UV photolithography exposure into a photoresist to define the waveguide area; (<b>b</b>) RIE to transfer the pattern into silicon (Si); (<b>c</b>) electron beam lithography to define the out-coupling grating-structures; (<b>d</b>) etching of Si waveguides. PMMA (positive tone) is used as a mask during the e-beam exposure process.</p> "> Figure 2
<p>(<b>a</b>) Step-and-repeat NIL process. (<b>b</b>) NPS 300 stepper.</p> "> Figure 3
<p>Schematics of the device based on a grating on waveguide. A relative change in dimensions occurs in the grating in the presence of an external environmental change. Two states are identified (unswollen and swollen) related to the behaviour of the selected hydrogel material. In the presence of an environmental change (water or pH), the hydrogel reaction leads to a morphological change of the grating structure.</p> "> Figure 4
<p>Multiple imprinted dies containing the sensor devices over 4 inch silicon wafer. (<b>a</b>,<b>b</b>) refer to the same wafer: in (<b>a</b>), the light applied through a camera is diffracted in the grating area of each die. The waveguide lines can be observed diffracting in (<b>b</b>). (<b>c</b>,<b>d</b>) Top view scanning electron microscopy images of the structures imprinted in the thermally curable hydrogel (<b>a</b>,<b>b</b>), where (<b>d</b>) gives a magnified view of (<b>c</b>).</p> "> Figure 5
<p>Normalised optical response of the sensor to water.</p> "> Figure 6
<p>Atomic force microscope images showing the patterned device in the dry (<b>a</b>) and the wet (<b>b</b>) state. The structures in the dry state are illustrated in (<b>a</b>), their expansion with water absorption and the partial closure of the spaces between the out-coupler grating lines are illustrated in (<b>b</b>).</p> "> Figure 7
<p>(<b>a</b>) Optical setup to test the sensor response to pH. (<b>b</b>) A magnified view of the cuvette environment.</p> "> Figure 8
<p>Optical signal response to the introduction of acid of pH 3 (<b>a</b>) and pH 6 (<b>b</b>). Initially, the sample was at neutral pH and dry, in equilibrium with the humidity in the room.</p> "> Figure 9
<p>Optical microscope images of the out-coupled light from the imprinted sensor in the dry state. In (<b>a</b>), the out-coupling in the grating region is well defined, while in (<b>b</b>), a divergence of the guided wave can be observed, indicating a poor-performance sensor.</p> ">
Abstract
:1. Introduction
2. Materials and Method
2.1. Material Formulation
2.2. Substrate Preparation
2.3. Stamp Manufacturing
2.4. Patterning Method
2.5. Sensor Evaluation Setup
3. Results and Discussion
3.1. Device Concept
3.2. Device Fabrication
3.3. How Water Affects the Sensor
3.4. How pH Affects the Sensor
4. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Parameter | Waveguide Width | Waveguide Height | Grating Height | Grating Line Width | Grating Period |
---|---|---|---|---|---|
Value | 1–5 μm | 0.5–1.0 μm | 100–150 nm | 400–500 nm | 700–800 nm |
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Francone, A.; Kehoe, T.; Obieta, I.; Saez-Martinez, V.; Bilbao, L.; Khokhar, A.Z.; Gadegaard, N.; Simao, C.D.; Kehagias, N.; Sotomayor Torres, C.M. Integrated 3D Hydrogel Waveguide Out-Coupler by Step-and-Repeat Thermal Nanoimprint Lithography: A Promising Sensor Device for Water and pH. Sensors 2018, 18, 3240. https://doi.org/10.3390/s18103240
Francone A, Kehoe T, Obieta I, Saez-Martinez V, Bilbao L, Khokhar AZ, Gadegaard N, Simao CD, Kehagias N, Sotomayor Torres CM. Integrated 3D Hydrogel Waveguide Out-Coupler by Step-and-Repeat Thermal Nanoimprint Lithography: A Promising Sensor Device for Water and pH. Sensors. 2018; 18(10):3240. https://doi.org/10.3390/s18103240
Chicago/Turabian StyleFrancone, Achille, Timothy Kehoe, Isabel Obieta, Virginia Saez-Martinez, Leire Bilbao, Ali Z. Khokhar, Nikolaj Gadegaard, Claudia Delgado Simao, Nikolaos Kehagias, and Clivia M. Sotomayor Torres. 2018. "Integrated 3D Hydrogel Waveguide Out-Coupler by Step-and-Repeat Thermal Nanoimprint Lithography: A Promising Sensor Device for Water and pH" Sensors 18, no. 10: 3240. https://doi.org/10.3390/s18103240