<p>Soft actuators and sensors are currently used in many industrial applications due to their capability to produce an accurate response. Researchers have studied dielectric electroactive polymers (DEAPs) because these types of structures can be utilized as actuators and as sensors being able to convert electrical energy into mechanical and vice versa. However, production of this kind of structures is complex and in general involve several steps that are time consuming. Customization of these types of structures will be ideal to enhance the performance of the devices based on the specific application. 3D printing technologies have emerged as innovative manufacturing processes that could improve fabrication speed, accuracy, and consistency with low cost. This additive manufacturing technique allows for the possibility of increased device complexity with high versatility. </p> <p>This research studied the potential of 3D printing technologies to produce DEAPs, soft actuators, and flexible sensors. The study presents novel designs of these composite flexible structures, utilizing the most flexible conductive and nonconductive materials available for fused deposition modeling, achieving versatility and high performance in the produced devices. <a>Produced DEAP actuators showed an actuation and electric resistivity higher than other electroactive structures like shape memory alloys and ferroelectric polymers.</a> In addition, this research describes the electromechanical characterization of a flexible thermoplastic polyurethane, (TPU), produced by additive manufacturing, including measurement of the dielectric constant, percentage radial elongation, tensile proprieties, pre-strain effects on actuation, surface topography, and measured actuation under high voltage. DEAP actuators were produced with two different printing paths, concentric circles and lines, showed an area expansion of 4.73% and 5.71% respectively. These structures showed high resistance to electric fields having a voltage breakdown of 4.67 kV and 5.73 kV respectively. <a>Those results are similar to the resistant of the most used dielectric material “VHB 4910”. </a></p> <p>The produced soft pneumatic actuators were successfully 3D printed in one continuous process without support material. The structures were totally sealed without the use of any sealing material or post process. Computational simulations were made to predict the response of the designed structures under different conditions. These results were compared with experimental results finding that the theoretical model is able to predict the response of the printed actuators with an error of less than 7%. This error is satisfactorily small for modeling 3D printed structures and can be further minimized by characterization of the elastomeric material. Besides that, two different grippers were designed based on the opening and closing movements of single bellows actuators. The functionality of both designs was simulated and tested, finding that both designs are capable lifting a heavier rigid structure. </p> <p>Finally, this study presents a computational simulation of a 3D printed flexible sensor, capable of producing an output signal based on the deformation caused by external forces. Two different sensors were designed and tested, working based on a capacitance and resistance change produced by structural deformation. Computational analysis indicate the capacitance sensor should undergo change of capacitance from 3 to 8.5 pF when is exposed to 30 kPa; and the resistance sensor should experience an increase from 101.8 to 103 kΩ when is exposed to 30 kPa. </p>

Electronic devices today are an integral part of human life thanks to state-of-the- art complementary metal oxide semiconductor (CMOS) technology. The progress in this area can be attributed to miniaturization driven by Moore’s Law. Further advancements in electronics are under threat from physical limits in dimensional scaling and hence new roadmaps for alternative materials and technologies are chased. Furthermore, the current era of Internet of things (IoT) and Internet of everything (IoE) has broaden the horizon to a plethora of unprecedented applications. The most prominent emerging fields are flexible and stretchable electronics. There has been significant progress in developments of flexible sensors, transistors, and alternative materials, etc. Nonetheless, there remains the unaddressed challenges of matching performance of the status-quo, packaging, interconnects, and lack of pragmatic integration schemes to readily complement existing state-of-the-art technology. In this thesis, a pragmatic heterogeneous integration strategy is presented to obtain high-performance 3D electronic systems using existing CMOS based integrated circuit (IC). Critical challenges addressed during the process are: reliable flexible interconnects, maximum area efficiency, soft-polymeric packaging, and heterogeneous integration compatible with current CMOS technology. First, a modular LEGO approach presents a novel method to obtain flexible electronics in a lock-and-key plug and play manner with reliable interconnects. A process of converting standard rigid IC into flexible LEGO without any performance degradation with a high-yield is shown. For the majority of healthcare and other monitoring applications in IoT, sensory array is used for continuous monitoring and spatiotemporal mapping activities. Here we present ultra-high-density sensory solution (1 million sensors) as an epitome of density and address each of the associated challenges. A generic heterogeneous integration scheme has been presented to obtain physically flexible standalone electronic system using 3D-coin architecture. This 3D-coin architecture hosts sensors on one side, readout circuit and data processing units embedded in the polymer, and the other side is reserved for antenna and energy harvester (photovoltaic). This thin platform (~ 300 μm) has achieved bending radius of 1 mm while maintaining reliable electrical interconnection using through-polymer-via (TPV) and soft-polymeric encapsulation. This coin integration scheme is compatible with existing CMOS technology and suitable for large scale manufacturing. Lastly, a featherlight non-invasive ‘Marine-Skin’ platform to monitor deep-ocean monitoring is presented using the heterogeneous integration scheme. Electrical and mechanical characterization has been done to establish reliability, integrity, robustness, and ruggedness of the processes, sensors, and multisensory flexible system.

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Les travaux de thèse portent sur le développement de méthodologies d'élaboration de dispositifs à base de polymères PDMS, destinés à des applications médicales. Ce travail s'appuie sur deux volets applicatifs : le développement de matrices de micro-capteurs capacitifs souples portables destinées à la mesure de champs de pression dans un contexte de suivi d'appuis du corps humain, et le développement d'une technique de collage réversible de composants PDMS dans une application de laboratoire sur puce en micro-fluidique. Dans ces travaux, les propriétés mécaniques du PDMS sont déterminées expérimentalement et à l'aide de modélisations numériques, afin d'identifier les éléments essentiels du dimensionnement des micro-capteurs capacitifs. Différents types de micro-capteurs de pression souples sont réalisés par un procédé de microfabrication à transfert de films. Ce procédé est optimisé à chacune de ses étapes afin d'obtenir un procédé fiable et reproductible. Les caractérisations électromécaniques montrent que les capteurs fabriqués sont opérationnels et adaptés aux applications médicales visées. Les capteurs de pression normale ont une variation de capacité de 3 à 17 % à 10 N - 300 kPa, adaptée à une application dentaire. Les capteurs à trois axes de sensibilité ont une résolution spatiale de 25 mm2, et une sensibilité de 4 % à 3 N en compression et 1,4 % par Newton en cisaillement pur, et sont adaptés à une application de mesure de la pression plantaire destinée à l'analyse de la marche et la détection des hyper-appuis. Par ailleurs, deux méthodes différentes permettant le collage réversible de composants PDMS sont développées. Les dispositifs microfluidiques fabriqués avec ces méthodes peuvent être utilisés avec jusqu'à 5 cycles de collage/décollage, et travailler à débit élevé (500 µL/min, correspondant à une pression de 148 kPa). Les méthodologies développées dans ces travaux ouvrent la voie à l'élaboration de dispositifs à base de PDMS performants et optimisés pour répondre à des cahiers des charges exigeants pour des applications biomédicales ciblées. / This thesis focuses on the development of methodologies dedicated to the development of PDMS-based devices, which are required in medical applications. Two objective applications are considered in this work: i) the development of wearable flexible micro-sensors arrays for measuring pressure fields on human body and ii) the development of a reversible bonding technique of PDMS components dedicated to microfluidic chips. In this work, the mechanical properties of PDMS are determined using experiments and computations; they allow identifying the essential elements of the design of capacitive micro-sensors. The manufacturing process is reliable and reproducible, and different types of flexible pressure sensor have been fabricated by a film transfer process. Electromechanical characterizations show that the fabricated sensors are fully operational and suitable for the intended applications. Normal pressure sensors have a capacitance change ranging from 3 to 17% under a 10 N - 300 kPa - load, which is suitable for dental applications. Fabricated triaxial sensor arrays have a spatial resolution of 25 mm2, and a sensitivity of 4% under 3 N load in compression, and 1.4% / N under shear. These features are suitable for plantar pressure measurements required in gait analyses or for the detection of over-pressures. Besides, two different process methods for the reversible bonding of PDMS devices are developed. The microfluidic devices fabrcitated with these methods can be used within up to 5 “bonding & peeling off” cycles, and can be working at high microfluidic flows (500 µL / min, corresponding to a pressure of 148 kPa). The methodologies developed in these works open the way to the design and fabrication of PDMS-based devices suitable for demanding biomedical applications.

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Die kürzliche globale COVID-19-Pandemie hat deutlich gezeigt, dass hohe medizinische Kosten eine große Herausforderung für unser Gesundheitssystem darstellen. Daher besteht eine wachsende Nachfrage nach personalisierten tragbaren Geräten zur kontinuierlichen Überwachung des Gesundheitszustands von Menschen durch nicht-invasive Erfassung physiologischer Signale. Diese Dissertation fasst die Forschung zur Laserkarbonisierung als Werkzeug für die Synthese flexibler Gassensoren zusammen und präsentiert die Arbeit in vier Teilen. Der erste Teil stellt ein integriertes zweistufiges Verfahren zur Herstellung von laserstrukturiertem (Stickstoff-dotiertem) Kohlenstoff (LP-NC) ausgehend von molekularen Vorstufen vor. Der zweite Teil demonstriert die Herstellung eines flexiblen Sensors für die Kohlendioxid Erfassung basierend auf der Laserumwandlung einer Adenin-basierten Primärtinte. Die unidirektionale Energieeinwirkung kombiniert mit der tiefenabhängigen Abschwächung des Laserstrahls ergibt eine neuartige geschichtete Sensorheterostruktur mit porösen Transducer- und aktiven Sensorschichten. Dieser auf molekularen Vorläufern basierende Laserkarbonisierungsprozess ermöglicht eine selektive Modifikation der Eigenschaften von gedruckten Kohlenstoffmaterialien. Im dritten Teil wird gezeigt, dass die Imprägnierung von LP-NC mit Molybdäncarbid Nanopartikeln die Ladungsträgerdichte verändert, was wiederum die Empfindlichkeit von LP-NC gegenüber gasförmigen Analyten erhöht. Der letzte Teil erläutert, dass die Leitfähigkeit und die Oberflächeneigenschaften von LP-NC verändert werden können, indem der Originaltinte unterschiedliche Konzentrationen von Zinknitrat zugesetzt werden, um die selektiven Elemente des Sensormaterials zu verändern. Basierend auf diesen Faktoren zeigte die hergestellte LP-NC-basierte Sensorplattform in dieser Studie eine hohe Empfindlichkeit und Selektivität für verschiedene flüchtige organische Verbindungen. / The recent global COVID-19 pandemic clearly displayed that the high costs of medical care on top of an aging population bring great challenges to our health systems. As a result, the demand for personalized wearable devices to continuously monitor the health status of individuals by non-invasive detection of physiological signals, thereby providing sufficient information for health monitoring and even preliminary medical diagnosis, is growing. This dissertation summarizes my research on laser-carbonization as a tool for the synthesis of functional materials for flexible gas sensors. The whole work is divided into four parts. The first part presents an integrated two-step approach starting from molecular precursor to prepare laser-patterned (nitrogen-doped) carbon (LP-NC). The second part shows the fabrication of a flexible LP-NC sensor architecture for room-temperature sensing of carbon dioxide via laser conversion of an adenine-based primary ink. By the unidirectional energy impact in conjunction with depth-dependent attenuation of the laser beam, a novel layered sensor heterostructure with a porous transducer and an active sensor layer is formed. This molecular precursor-based laser carbonization method enables the modification of printed carbon materials. In the third part, it is shown that impregnation of LP-NC with molybdenum carbide nanoparticle alters the charge carrier density, which, in turn, increases the sensitivity of LP-NC towards gaseous analytes. The last part explains that the electrical conductivity and surface properties of LP-NC can be modified by adding different concentrations of zinc nitrate into the primary ink to add selectivity elements to the sensor materials. Based on these factors, the LP-NC-based sensor platforms prepared in this study exhibited high sensitivity and selectivity for different volatile organic compounds.

Man’s desire to replicate/mimic the nature’s creation provided an impetus and inspiration to the rapid advancements and progress made in the sensors and actuators technology. A normal human being has five basic sensory organs, which helps and guides him in performing the routine tasks. This underlines the importance of basic sensory organs in a human life. In a similar fashion, sensors and actuators are of paramount importance for most of the science and engineering applications. The aim of the present thesis work is to explore the application of piezoelectric ZnO thin films deposited on a flexible substrate for the development of sensors and actuators. Detailed study was performed on the suitability of three different flexible substrates namely Phynox, Kapton and Mylar. However, Phynox alloy substrate was found to be a suitable substrate material for the above mentioned applications. Sputtering technique was chosen for the deposition of ZnO thin films on to Phynox substrate. The necessary process parameters were optimized to achieve good quality piezoelectric thin films. In the present work, sensors have been developed by utilizing the direct piezoelectric effect of ZnO thin films deposited on Phynox alloy substrate. These includes a flow sensor for gas flow rate measurement, impact sensor for non-destructive material discrimination study and a Thin Film Sensor Array (TFSA) for monitoring the impact events. On the other hand, using the converse piezoelectric effect of ZnO thin films, actuators have also been developed. These include a thin film micro actuator and a Thin Film Micro Vibrator (TFMV) for vibration testing of micro devices. The thesis is divided into following seven chapters. Chapter 1: This chapter gives a general introduction about sensors and actuators, piezoelectric thin films, flexible substrates, thin film deposition processes and characterization techniques. A brief literature survey of different applications of piezoelectric thin films deposited on various flexible substrates in device development is presented. Chapter 2: A novel flexible metal alloy (Phynox) and its properties along with its applications are discussed in this chapter. ZnO thin films were deposited on Phynox substrate by Rf reactive magnetron sputtering technique. The sputtering process parameters such as: Ar:O2 gas ratio, substrate temperature and RF power were optimized for the deposition of good quality piezoelectric ZnO thin films. The deposited ZnO thin films were characterized using XRD, SEM, AFM and d31 coefficient measurement techniques. Chapter 3: It reports on the comparative study of properties of piezoelectric ZnO thin films deposited on three different types of flexible substrates. The substrate materials employed were a metal alloy (Phynox), polyimide (Kapton), and polyester (Mylar). Piezoelectric ZnO thin films deposited on these flexible substrates were characterized by XRD, SEM, AFM and d31 coefficient measurement techniques. A vibration sensing test was also performed for the confirmation of good piezoelectric property. Compared to the polymer flexible substrates, the metal alloy flexible substrate (Phynox) was found to be more suitable for integrating ZnO thin film for sensing applications. Chapter 4: The development of a novel gas flow sensor for the flow rate measurement in the range of L min-1 is presented in this chapter. The sensing element is a Phynox alloy cantilever integrated with piezoelectric ZnO thin film. A detailed theoretical analysis of the experimental set–up showing the relationship between output voltage generated and force at a particular flow rate has been discussed. The flow sensor is calibrated using an in-house developed testing set-up. Chapter 5: This chapter is divided into two sections. Section 5.1 reports on the development of a novel packaged piezoelectric thin film impact sensor and its application in non-destructive material discrimination studies. Different materials (Iron, Glass, Wood and Plastic) were successfully discriminated by using the developed impact sensor. The output response of impact sensor showed good linearity and repeatability. The impact sensor is sensitive, reliable and cost-effective. Section 5.2 reports on the development of a Thin Film Senor Array (TFSA) for monitoring the location and magnitude of the impact force. The fabricated TFSA consists of evenly distributed ZnO thin film sensor array. Chapter 6: It consists of two sections. Section 6.1 reports on the fabrication of micro actuator using piezoelectric ZnO thin film integrated with flexible Phynox substrate. A suitable concave Perspex mounting was designed for the actuator element. The actuator element was excited at different frequencies for the supply voltages of 2V, 5V and 8V. The developed micro actuator has the potential to be used as a micro pump for pumping nano liters to micro liters of fluids. Section 6.2 reports the design and development of a portable ready to use Thin Film Micro Vibrator (TFMV). The TFMV is capable of providing the vibration amplitude in the range of nanometer to micrometer. A thin silicon diaphragm was used as a test specimen for its vibration testing studies using the developed TFMV. The TFMV is light-weight and have internal battery, hence no external power supply is required for its functioning. Chapter 7: The first section summarizes the salient features of the work presented in this thesis. In the second section the scope for carrying out the further work is given.

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<p>The development of reliable, robust and low-cost sensor devices is growing in importance and an ongoing challenge. From environmental monitoring and household safety to food and biopharmaceutical industries, the necessity for specific analyte detection is crucial. Over the years researchers have come up with myriad materials that can be used for efficient sensing devices. The materials employed are governed by application and performance criteria as well as the sensing mechanism, which might be based on physical or chemical principles. In this thesis, two different types of electrochemical sensor technologies were examined with special attention paid to the application of the devices, the materials used, and their feasibility for scalable manufacturing.</p> <p>In the first study, binary mixtures of conducting and semiconducting nanomaterials were explored as promising candidates for the manufacturing of low-cost ethylene sensor on flexible substrates. Ethylene (C2H4) is a small plant hormone which has been shown to affect the growth and senescence of flowers, leaves and fruits. Currently available devices have demonstrated high ethylene sensitivities with great potential for technology size reduction; however, some are not practical for use outside of the laboratory, lack portability, or require more research to demonstrate their reproducibility and stability in different environments, as well as selectivity to C2H4 in large-scale applications. Conductometric gas sensors based on a combination of carbon nanotubes (CNTs) and exfoliated molybdenum disulfide (MoS2) coated with molecular receptors is demonstrated for the selective detection of ethylene, including details on materials preparation, manufacturing, and characterization. Mixtures of CNTs and exfoliated MoS2 were deposited onto screen-printed interdigitated electrodes on plastic substrates, with optimization for scalable and continuous manufacturing by roll-to-roll methods. C2H4 detection levels of 0.1 ppm were readily achieved with responses on the second timescale.</p> <p>The second sensor technology shows how thin-film potentiometric electrodes based on ion-selective membranes can be designed to tolerate sterilizing radiation while providing excellent performance and signal stability. This sensor's development was motivated by the expanding need for single-use bioreactor systems in the biopharmaceutical industry, which require strict control over cell culture conditions for several weeks or more. Until recently, critical analysis has been conducted mostly by offline or “at-line” sampling of aliquots withdrawn from the sterile bioreactor. The latter is inefficient and can increase the risk of contamination. Inspired by the challenges related to cost, integration and performance following irradiation a potentiometric pH electrode was developed, intended for single-use applications. It was shown to be radiation-tolerant while providing reliable data comparable to a commercial pH meter over a period of three months. The electrodes exhibited quasi-linear signal drifts of +0.28 mV/day or 0.005 pH units/day. Thin-film γ-irradiated electrodes could provide accurate pH readings in sterilized culture media using a single-point calibration, within 0.07 pH units of a commercial meter with glass electrode and daily calibration. Furthermore, to advance the development of market-ready sensors past the conceptual stage, a few automated processes for scalable membrane deposition were investigated.</p>