As the world population grows, a persistent pressure on natural resources remains. Resource requirements have extensively expanded due to industrialization. Several technological advancements continually aim to alleviate these resource shortages by targeting existing shortcomings in effective and efficient material design. Practical, high-performing, and economical materials are needed in several key application areas, including energy storage, energy harvesting, electronics, catalysis, and water purification. Further development into high-performing and economical materials remain imperative. Innovators must seek to develop technologies that overcome fundamental limitations by designing materials and devices which address resource challenges. Carbon serves as a versatile material for a wide range of applications including purification, separation, and energy storage owing to excellent electrical, physical, and mechanical properties. One-dimensional (1D) carbon fiber in particular is renowned for excellent strength with high surface-to-volume ratio and is widely commercially available. Although an exceptional candidate to address current energy and environmental needs, carbon fibers require further investigation to be used to their full potential. Emerging strategies for carbon fiber design rely on developing facile synthetic routes for controlled carbon structures. The scientific community has shown extensive interest in porous carbon fabrication owing to the excellent performance enhancement in separation, filtration, energy storage, energy conversion, and several other applications. This dissertation both reviews and contributes to the recent works of porous carbon and their applications in energy and environmental sciences. The background section shows recent development in porous carbon and the processing methods under investigation and current synthetic methods for designing porous carbon fibers (PCF). Later sections focus on original research. A controlled radical polymerization method, reversible addition-fragmentation chain transfer (RAFT), enabled a synthetic design for a block copolymer precursor, poly(methyl methacrylate) (PMMA) and polyacrylonitrile (PAN). The block copolymer (PMMA-b-PAN) possesses a unique microphase separation when electrospun and develop narrowly disperse mesopores upon carbonization. The PMMA and PAN domains self-assemble in a kinetically trapped disordered network whereby PMMA decomposes and PAN cross-links into PCF. The initial investigation highlights the block copolymer molecular weight and compositional design control for tuning the physical and electrochemical properties of PCF. Based on this study, mesopore (2 – 50 nm) size can be tuned between 10 – 25 nm while maintaining large surface areas, and the PAN-derived micropores (< 2 nm). The mesopores and micropores both contribute to the development of the unique hierarchical porous carbon structure which brings unprecedented architectural control. The pore control greatly contributes to the carbon field as the nano-scale architecture significantly influences performance and functionality. The next section uses PCF to clean water sources that are often tainted with undesirable ions such as salts and pollutants. Deionization or electrosorption is an electrochemical method for water purification via ion removal. I employed the PCFs as an electrode for deionization because of their high surface area and tunable pore size. Important for deionization, the adsorption isotherms and kinetics highlight the capacity and speed for purification of water. I studied PCF capacitive filtration on charged organic salts. Because PCF have both micropores and mesopores, they were able to adsorb ions at masses exceeding their own weight. The PFC adsorption efficiency was attributed to the diffusion kinetics within the hierarchical porous system and the double layer capacitance development on the PCF surface. In addition, based on the mechanism of adsorption, the PCFs showed high stability and reusability for future adsorption/desorption applications. The PCF performance as an electrosorption material highlights the rational design for efficient electrodes by hierarchical interconnected porosity. Another application of PFCs is updating evaporative desalination methods for water purification. Currently distillation is not widely used as a source of potable water owing to the high cost and energy requirement. Solar desalination could serve as a low-cost method for desalination; however, the evaporation enthalpy of water severely limits practical implementation. Here I apply the pore design of PCF as a method for water nano-confinement. Confinement effects reduce water density and lowers evaporation enthalpy. Desalination in PCF were studied in pores < 2 nm to 22 nm. The PCF pore size of ~ 10 nm was found to be the peak efficiency and resulted in a ~ 46% reduction in enthalpy. Interestingly, the PCF nano-confinement also contributed to the understanding in competing desorption energy for evaporation in micropores. The pore design in PCF also shows confinement effects that can be implemented in other environmental applications. Lastly, the block copolymer microphase morphology was explored in a vapor induced phase separation system. The resulting PCF properties showed a direct influence from the phase separation caused by nonsolvent. At low nonsolvent vapor, a disordered microphase separation occurred, however upon application of nonsolvent vapor, the polymer chains reorganized. The reorganization initially improved mechanical properties by developing more long-range ordered graphic chains in the PAN-derived carbon. However, at higher nonsolvent vapor concentrations, the fibers experienced polymer precipitation which resulted in bead and clump formation in the fiber mats. The beads and clumps lowered both mechanical properties and electrochemical performance. The vapor induced phase separation showed a method for enhancing mechanical properties without compromising electrochemical performance in flexible carbon fibers. / Doctor of Philosophy / Nanomaterials possess mechanical, physical, and electrical properties to address important growing demands for precious resources such as clean water and energy. Many advancements in nanomaterials focus on improving fine-tune architectures which facilitate efficiency in composites, filtration systems, catalytic systems, energy storage devices, and electronics. Carbon material has remained a valuable candidate in these fields owing to its abundancy economical cost, and excellent properties. Several carbon forms provide unique characteristics including 0D dots, 1D fibers, 2D sheets, and 3D monoliths. Of these, 1D fibers possess excellent strength, resiliency, and conductivity and have been commercially employed in modern automotive, airplanes, membranes, and conductors. However, traditional carbon fiber fabrication does not match the growing needs in performance. Therefore, in this dissertation I explore the design and processing of carbon fibers for controlled architectures. These designs were then systematically studied in filtration systems, solar desalination, and flexible electronics. Block copolymers provide a new way to combine polymers for drastically new materials and effects. Firstly, I conducted a comprehensive study on the synthesis and composition of this block copolymer which laid the foundation for future carbon fiber design. The polymer consists of two chains – one chain to develop carbon structures upon heating; the second which decomposes into pores upon heating. Therefore, with these two chains, a highly porous carbon fiber can be created. The reaction I studied could mostly be controlled with time to change the length of each chain. Ultimately, the pore size and surface area depend on the relative lengths of each chain. Future studies, including ones in this work, could therefore tune pore size and surface area for many applications. Carbon fibers with graphitic structure are inherently conductive and thereby attract charged molecules in a solution. Diffusion and capacity serve as major factors in these types of systems. With the aforementioned control of the carbon fibers a diffusion study was conducted with charged pollution ions. Owing to the conductive nature, a voltage supply was attached to the fibers, which would adsorb ions electrostatically, termed "electrosorption". The electrosorption performance within the carbon fibers elucidated the interconnected porous structure and how ions orientate themselves along the surface of the fibers. In addition, with the development of ion orientation along the surface of the fibers, a greater than 1:1 ratio of carbon weight to ion weight adsorbed developed owing to the diffusion and ion stacking capabilities. Additionally, the study provides deeper investigation into movement of ions within confined nano-porous material. The ever-growing need for renewable resources such as fresh water has pressured development into more efficient material. Solar desalination has attractive qualities which makes it a focus for micro-scale studies. One of the major limitations lies in the high energy input change liquid water into vapor. At 100 °C for boiling, desalination lacks sufficient efficiency for large-scale applications in evaporation. However, by utilizing nano-scale material, the fundamental properties of water can be altered. The carbon fibers were then created with various nano-pore sizes which revealed nano-confinement effects when subject to solar heating. With the shrinking of pore sizes, the density of water also decreased. A lower density means less energy was required to convert water from a liquid to a vapor state. The carbon fibers helped reveal real applications into confinement effects on water based on pore size. Apart from just desalination, this means future environmental application can utilize this knowledge for more effective and smart designs. The carbon fibers outstanding electrical and mechanical properties have spurred research and development since the mid-1900s. Since then, carbon fiber technologies have grown from facile and efficient productions means, to high end, high performance smart design. The work presented here furthers two major components: first, the high-performance design of porous carbon fiber; second, the fundamental principles in nano-material properties and their applications. By first constructing a design of polymer synthesis and then subsequent studies, development of nano-porous carbon energy progresses knowledge on smart and efficient designs. These materials provide a platform for future energy and environmental sciences.

Non-planar additive manufacturing (AM) technologies, such as microextrusion 3D printing processes, offer the ability to fabricate conformal electronics with impressive structure and function on curvilinear substrates. Although various available methods offer conformal 3D printing capability on objects with limited geometric complexity, a number of challenges remain to improve feature resolution, throughput, materials compatibility, resultant function and properties of printed components, and application to substrates of varying topography. Hence, the overall objective of this dissertation was to create new non-planar AM processes that are compatible with personalized and anatomical computer-aided design workflows for the fabrication of conformal electronics and form-fitting wearables. After reviewing the current state of knowledge and state of the art, significant challenges in non-planar AM have been identified as: 1) limited non-planar AM path planning capability that synergizes with personalized or anatomical object surface modification, 2) limited approaches for printed and non-printed component integration on non-planar substrates. To address these challenges, a template-based reverse engineering workflow is proposed for conformal 3D printing electronics and form-fitting wearable devices on anatomical structures. This work was organized into three complementary tasks that enhance non-planar AM capabilities: 1） To achieve anatomical tissue-sensor integration, 3D scanning-based point cloud data acquisition and customized 3D printable conductive ink are proposed for capturing the topographical information of patient-specific malformations and integrating conformal sensing electronics across anatomical tissue-device interface. 2） To fabricate conformal antennas on flexible thin-film polymer substrates, a versatile method for microextrusion 3D printing of conformal antennas on thin film-based structures of random topography is proposed to control the ink deposition process across the curvilinear surfaces of freeform Kapton-based origami. 3） To simplify the fabrication process of form-fitting wearable devices with fiber-based form factors and self-powered capability, an innovative 3D printing process is proposed to achieve coaxial multi-material extrusion of metal-elastomer triboelectric fibers. By developing new advanced non-planar printing processes and conformal toolpath programming strategies, the utility of non-planar AM could be further expanded for fabricating various personalized implantable and wearable multi-functional systems, including novel 3D electronics. In summary, this work advances capability in additive manufacturing processes by providing new advances in multi-material extrusion processes and personalized device design and manufacturing workflows. / Doctor of Philosophy / The ability to assemble electronic devices on three-dimensional objects with complex geometry is essential for developing next-generation wearable devices. Additive manufacturing processes, commonly referred to as 3D printing, now offer the ability to fabricate conformal electronics on surfaces and objects with non-planar geometry. This dissertation aims to expand non-planar 3D printing capabilities for applications to objects with anatomical or personalized structures, such as patient-specific malformation and origami. The proposed methods in this dissertation are focused on addressing challenges, such as the acquisition of object 3D topographical data, material selection, and tool path programming for objects that exhibit anatomical geometry. The utility of the proposed methods is demonstrated with practical applications to 3D-printed conformal electronics and wearable devices for monitoring human behavior and organ healthcare. This dissertation contributes to improving manufacturing capability and outcomes of 3D-printed form-fitting wearable and implantable devices. Future work may emphasize developing biocompatible functional ink and toolpath programming algorithms with real-time adaptation capability.

This dissertation will outline solution processable materials and fabrication techniques to manufacture flexible electronic devices from them. Conductive ink formulations and inkjet printing of gold and silver on plastic substrates were examined. Line patterning and mask printing methods were also investigated as a means of selective metal deposition on various flexible substrate materials. These solution-based manufacturing methods provided deposition of silver, gold and copper with a controlled spatial resolution and a very high electrical conductivity. All of these procedures not only reduce fabrication cost but also eliminate the time-consuming production steps to make basic electronic circuit components. Solution processable semiconductor materials and their composite films were also studied in this research. Electrically conductive, ductile, thermally and mechanically stable composite films of polyaniline and sulfonated poly (arylene ether sulfone) were introduced. A simple chemical route was followed to prepare composite films. The electrical conductivity of the films was controlled by changing the weight percent of conductive filler. Temperature dependent DC conductivity studies showed that the Mott three dimensional hopping mechanism can be used to explain the conduction mechanism in composite films. A molecular interaction between polyaniline and sulfonated poly (arylene ether sulfone) has been proven by Fourier Transform Infrared Spectroscopy and thermogravimetric analysis. Inkjet printing and line patterning methods also have been used to fabricate polymer resistors and field effect transistors on flexible substrates from poly-3-4-ethyleneoxythiophene/poly-4-sytrensulfonate. Ethylene glycol treatment enhanced the conductivity of line patterned and inkjet printed polymer thin films about 900 and 350 times, respectively. Polymer field effect transistors showed the characteristics of traditional p-type transistors. Inkjet printing technology provided the transfer of semiconductor polymer on to flexible substrates including paper, with high resolution in just seconds. / Ph. D.

A process has been developed to make the dielectric layer for organic thin-film transistors (OTFTs) in a roll-to-roll vacuum web coater environment. This dielectric layer combined with an organic semiconductor layer and metal layer deposited in vacuum allows a solvent-free process to make organic/inorganic multilayer structures for thin-film electronic devices on a flexible substrate at, potentially, high speed. The polymeric gate dielectric layers were fabricated by flash evaporation of acrylic monomers onto a polymer film with pre-patterned metal gates followed by radiation curing by electron beam, ultra-violent light (UV) or plasma. With a non-polar dielectric surface, charge carrier mobility (&mu;) of 1 cm²-V^-1s^-1; on/off curren ratio of 10⁸, sub-threshold swing (SS) of 0.3 V/decade and saturated output curve were routinely achieved in dinaphtho-[2,3-b:2'3'-f]thieno[3,2-b]thiophene (DNTT) transistors with dielectric layer of tripropylene glycol diacrylate (TPGDA) of ~400 nm. Apart from the TPGDA, monomer formulas including 1,6-Hexanediol diacrylate (HDDA) as well as several commercial acrylic resins have been used to make the dielectric layer. The highest areal capacitance of 41nF-cm^-2 was achieved with a pin-hole free film of less than 100 nm made of an acrylate mixture resin. A non-polar dielectric surface treatment layer has been developed based on flash evaporation of lauryl acrylate and HDDA mixture. The transistors with the buffer layer showed constant performance and a mobility fivefold greater than those of untreated samples. The effect of humidity, oxygen, and light during switching cycles of both pentacene and DNTT transistors were studied. Water and oxygen/illumination had a distinct effect on both pentacene and DNTT transistors. Oxygen leads to acceptor-like charge traps under illumination, which shifted the turn-on voltage (V_to) to more positive values. In contrast, water in transistors gave rise to donor-like charge traps, which shifted the V_to and the threshold voltage (V_T) more negatively. The DNTT devices showed good stability in dry air without encapsulation, while pentacene transistors degraded with either repeating measurement or long term storage. A DNTT transistor with a PS-coated TPGDA dielectric layer showed stable drain current (I_d) of ~105A under bias stress of the gate voltage (em>V_g) of -20V and the drain voltage (em>V_d) of -20V for at least 144 hours. The V_to shift after the stress was less than 5 V and was recoverable when the device was kept in dry air for a few days. Possible reasons for the V_to shift have been discussed.

Organic electronics is the study of organic materials with electronic functionality and the applications of such materials. In the 1970s, the discovery that polymers can be made electrically conductive led to an explosion within this field which has continued to grow year by year. One of the attractive features of organic electronic materials is their inherent mechanical flexibility, which has led to the development of numerous flexible electronics technologies such as organic light emitting diodes and solar cells on flexible substrates. The possibility to produce electronics on flexible substrates like plastic or paper has also had a large impact on the field of printed, electronics where inks with electronic functionality are used for large area fabrication of electronic devices using classical printing methods, such as screen printing, inkjet printing and flexography. Recently, there has been a growing interest in the use of cellulose in organic and printed electronics, not only as a paper substrate but also as a component in composite materials where the cellulose provides mechanical strength and favorable 3D-microstructures. Nanofibrillated cellulose is composed of cellulose fibers with high aspect-ratio and diameters in the nanometer range. Due to its remarkable mechanical strength, large area-to-volume ratio, optical transparency and solution processability it has been widely used as a scaffold or binder for electronically active materials in applications such as batteries, supercapacitors and optoelectronics. The focus of this thesis is on flexible devices based on conductive polymers and can be divided into two parts: (1) Composite materials of nanofibrillated cellulose and the conductive polymer PEDOT:PSS and (2) patterning of vapor phase polymerized conductive polymers. In the first part, it is demonstrated how the combination of cellulose and conductive polymers can be used to make electronic materials of various form factors and functionality. Thick, freestanding and flexible “papers” are used to realize electrochemical devices such as transistors and supercapacitors while lightweight, porous and elastic aerogels are used for sensor applications. The second focus of the thesis is on a novel method of patterning conductive polymers produced by vapor phase polymerization using UV-light. This method is used to realize flexible electrochromic smart windows with high-resolution images and tunable optical contrast.

In this dissertation, a carbon nanotube thin-film transistor is fabricated on a flexible substrate. Combined printing and stamping techniques are used for the fabrication. An ink-jet printing technique is used to form the gate, source, and drain electrodes as well as the dielectric layer. A self aligned carbon nanotube (CNT) thin film is formed by using a new modified dip coat technique before being transferred to the device substrate. This novel modified dip-coat technique utilizes the capillary effect of a liquid solution rising between gaps to coat CNT solution on a large area of the substrate while consuming minimal CNT solution. Several key solutions are addressed to solve the fabrication problems. (1) The source/drain contact with the CNT channel is developed by using droplets of silver ink printed on the source/drain areas prior to applying CNT thin. The wet silver ink droplets allow the silver to "wet" the CNT thin-film area and enable good contact with the source and drain contact after annealing. (2) A passivation layer to protect the device channel is developed by bonding a thin Kapton film on top of the device channel. This thin Kapton film is also used as the media for transferring the aligned CNT thin-film on the device substrate. Using this technique, printing the passivation layer can be avoided, and it prevents the inter-diffusion of the liquid dielectric into the CNT porous thin-film. (3) A simple and cost effective technique to form multilayer metal interconnections on flexible substrate is developed and demonstrated. Contact vias are formed on the second substrate prior bonding on the first substrate. Ink-jet printing is used to fill the silver ink into the via structure. The printed silver ink penetrates through the vias to contact with the contact pads on the on the bottom layer, followed by an anneal process. High drain current of 0.476mA was obtained when V[subscript G]= -3V and source-drain voltage (V[subscript DS]) was -1.5V. A bending test was performed on the CNT TFT showing less than a 10% variation in performance. A bending test was also performed on via structures, which yielded less than a 5% change in resistance. The developed CNT TFT is used to form a switch in a phase shifter for a flexible phased-array antenna (PAA). Four element 1-dimensional and 2-dimensional phased-array antennae are fabricated and characterized. Multilayer metal interconnects were used to make a complete PAA system. For a 2-bit 1x4 PAA system, by controlling the ON/OFF states of the transistors, beam steering of a 5.3GHz signal from 0° to -27° has been demonstrated. The antenna system also shows good stability and tolerance under different bending radii of curvature. A 2-bit 2x2 PAA system was also fabricated and demonstrated. Two dimensional beam steering of a 5.2GHz signal at an angle of [theta]=20.7° and [phi]=45° has been demonstrated. The total efficiency of the 1-dimensional and 2-dimensional PAA systems are 42% and 46%, respectively. / text

Radio frequency identification (RFID) and sensing are two key technologies enabling the Internet of Things (IoT). Development of RFID tags augmented with sensing capabilities (RFID sensor tags) would allow a variety of new applications, leading to a new paradigm of the IoT. Chipless RFID sensor technology offers a low-cost solution by eliminating the need of an integrated circuit (IC) chip, and is hence highly desired for many applications. On the other hand, printing technologies have revolutionized the world of electronics, enabling cost-effective manufacturing of large-area and flexible electronics. By means of printing technologies, chipless RFID sensor tags could be made flexible and lightweight at a very low cost, lending themselves to the realization of ubiquitous intelligence in the IoT era. This thesis investigated three construction methods of printable chipless RFID humidity sensor tags, with focus on the incorporation of the sensing function. In the first method, wireless sensing based on backscatter modulation was separately realized by loading an antenna with a humidity-sensing resistor. An RFID sensor tag could then be constructed by combining the wireless sensor with a chipless RFID tag. In the second method, a chipless RFID sensor tag was built up by introducing a delay line between the antenna and the resistor. Based on time-domain reflectometry (TDR), the tag encoded ID in the delay time between its structural-mode and antenna-mode scattering pulse, and performed the sensing function by modulating the amplitude of the antenna-mode pulse. In both of the above methods, a resistive-type humidity-sensing material was required. Multi-walled carbon nanotubes (MWCNTs) presented themselves as promising candidate due to their outstanding electrical, structural and mechanical properties. MWCNTs functionalized (f-MWCNTs) by acid treatment demonstrated high sensitivity and fast response to relative humidity (RH), owing to the presence of carboxylic acid groups. The f-MWCNTs also exhibited superior mechanical flexibility, as their resistance and sensitivity remained almost stable under either tensile or compressive stress. Moreover, an inkjet printing process was developed for the f-MWCNTs starting from ink formulation to device fabrication. By applying the f-MWCNTs, a flexible humidity sensor based on backscatter modulation was thereby presented. The operating frequency range of the sensor was significantly enhanced by adjusting the parasitic capacitance in the f-MWCNTs resistor. A fully-printed time-coded chipless RFID humidity sensor tag was also demonstrated. In addition, a multi-parameter sensor based on TDR was proposed.The sensor concept was verified by theoretical analysis and circuit simulation. In the third method, frequency-spectrum signature was utilized considering its advantages such as coding capacity, miniaturization, and immunity to noise. As signal collision problem is inherently challenging in chipless RFID sensor systems, short-range identification and sensing applications are believed to embody the core values of the chipless RFID sensor technology. Therefore a chipless RFID humidity sensor tag based on near-field inductive coupling was proposed. The tag was composed of two planar inductor-capacitor (LC) resonators, one for identification, and the other one for sensing. Moreover, paper was proposed to serve as humidity-sensing substrate for the sensor resonator on accounts of its porous and absorptive features. Both inkjet paper and ordinary packaging paper were studied. A commercial UV-coated packaging paper was proven to be a viable and more robust alternative to expensive inkjet paper as substrate for inkjet-printed metal conductors. The LC resonators printed on paper substrates showed excellent sensitivity and reasonable response time to humidity in terms of resonant frequency. Particularly, the resonator printed on the UV-coated packaging paper exhibited the largest sensitivity from 20% to 70% RH, demonstrating the possibilities of directly printing the sensor tag on traditional packages to realize intelligent packaging at an ultra-low cost. / <p>QC 20150326</p>

Le diagnostic de l'occlusion dentaire reste actuellement un défi majeur pour les chirurgiens-dentistes. Des outils dédiés existent, comme le papier à articuler et le T-Scan®, mais sont limités pour diverses raisons. L'objectif de cette thèse est alors de développer un nouvel outil sous forme de matrice de capteurs de pression sur substrat flexible alliant les avantages des outils nommés précédemment, à savoir un produit électronique, informatisé et de faible épaisseur pour ne pas être intrusif. Nous avons choisi une technologie piézorésistive et l'utilisation de jauges de contrainte en silicium microcristallin. Ce matériau est déposé à basse température (< 200°C) directement sur substrat Kapton® par PECVD (Plasma Enhanced Chemical Vapor Deposition) dans une perspective de faible coût. Ces jauges ont d'abord été caractérisées mécaniquement et électriquement lors de tests de courbure. Les facteurs de jauge longitudinaux et transversaux du silicium microcristallin ont été étudiés afin de maîtriser son comportement sous déformation. Les dispositifs restent fonctionnels jusqu'à des contraintes de 0,6 %, à partir de laquelle des dégradations apparaissent. Ces valeurs de contraintes permettent d'atteindre des rayons de courbure de l'ordre du millimètre pour des substrats de 25 µm d'épaisseur. Deux types de matrices ont ensuite été développées : une première de 800 jauges pour l'étude de la surface occlusale d'une dent puis une seconde de 6400 jauges pour l'étude d'une moitié de mâchoire. Dans les deux cas, des corrélations intéressantes entre le papier à articuler et nos réponses électriques ont été observées lors de caractérisations en conditions « semi-réelles » à l'aide d'un articulateur dentaire. Ces deux prototypes ont ainsi permis une preuve de concept fonctionnelle de l'objectif visé en utilisant des jauges en silicium microcristallin. / Dental occlusion diagnosis is still a major challenge for dentists. A couple of tools are dedicated to occlusal analysis, such as articulating papers and the T-Scan® system, but they are limited for various reasons. That's why, the goal of this thesis is to develop a novel system consisting in pressure sensor arrays on flexible substrates combining the positive aspects of both previously cited tools: an electronic and computerized system, on a very thin non-invasive flexible substrate. We chose a piezoresistive technology based on microcrystalline silicon strain gauges and 25-µm- or 50-µm-thick Kapton® substrates. Microcrystalline silicon is deposited directly on plastic at low temperature (< 200°C) using PECVD technique (Plasma Enhanced Chemical Vapor Deposition) in a cost-effective solution perspective. Strain gauges have firstly been characterized using bending tests. Longitudinal and transversal gauge factors have been studied in order to understand the behavior of our deposited materials under bending. Those gauges remained functional until strains up to 0.6 % and degradations appeared for higher values. These values correspond to bending radius on the order of 1 mm for 25-µm-thick substrates. Then, those gauges have been integrated in arrays with two different designs: one was an 800-element array to study the occlusal surface of one tooth, and the second was a 6400-element array to study the occlusal surface of a hemiarcade. Those prototypes have showed interesting correlations between articulating paper marks and our electrical responses during characterizations using a dental articulator to simulate a human jaw. Thus, we have developed in this work a proof-of-concept of a flexible strain sensor using microcrystalline silicon dedicated to dental occlusion diagnosis.

abstract: ABSTRACT This work seeks to develop a practical solution for short range ultrasonic communications and produce an integrated array of acoustic transmitters on a flexible substrate. This is done using flexible thin film transistor (TFT) and micro electromechanical systems (MEMS). The goal is to develop a flexible system capable of communicating in the ultrasonic frequency range at a distance of 10 - 100 meters. This requires a great deal of innovation on the part of the FDC team developing the TFT driving circuitry and the MEMS team adapting the technology for fabrication on a flexible substrate. The technologies required for this research are independently developed. The TFT development is driven primarily by research into flexible displays. The MEMS development is driving by research in biosensors and micro actuators. This project involves the integration of TFT flexible circuit capabilities with MEMS micro actuators in the novel area of flexible acoustic transmitter arrays. This thesis focuses on the design, testing and analysis of the circuit components required for this project. / Dissertation/Thesis / M.S. Electrical Engineering 2012

abstract: This work explores how flexible electronics and display technology can be applied to develop new biomedical devices for medical, biological, and life science applications. It demonstrates how new biomedical devices can be manufactured by only modifying or personalizing the upper layers of a conventional thin film transistor (TFT) display process. This personalization was applied first to develop and demonstrate the world's largest flexible digital x-ray detector for medical and industrial imaging, and the world's first flexible ISFET pH biosensor using TFT technology. These new, flexible, digital x-ray detectors are more durable than conventional glass substrate x-ray detectors, and also can conform to the surface of the object being imaged. The new flexible ISFET pH biosensors are >10X less expensive to manufacture than comparable CMOS-based ISFETs and provide a sensing area that is orders of magnitude larger than CMOS-based ISFETs. This allows for easier integration with area intensive chemical and biological recognition material as well as allow for a larger number of unique recognition sites for low cost multiple disease and pathogen detection. The flexible x-ray detector technology was then extended to demonstrate the viability of a new technique to seamlessly combine multiple smaller flexible x-ray detectors into a single very large, ultimately human sized, composite x-ray detector for new medical imaging applications such as single-exposure, low-dose, full-body digital radiography. Also explored, is a new approach to increase the sensitivity of digital x-ray detectors by selectively disabling rows in the active matrix array that are not part of the imaged region. It was then shown how high-resolution, flexible, organic light-emitting diode display (OLED) technology can be used to selectively stimulate and/or silence small groups of neurons on the cortical surface or within the deep brain as a potential new tool to diagnose and treat, as well as understand, neurological diseases and conditions. This work also explored the viability of a new miniaturized high sensitivity fluorescence measurement-based lab-on-a-chip optical biosensor using OLED display and a-Si:H PiN photodiode active matrix array technology for point-of-care diagnosis of multiple disease or pathogen biomarkers in a low cost disposable configuration. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2014