Os objetivos desta tese são: o estudo e aprimoramento dos diferentes parâmetros geométricos e de processo de fabricação de guias de onda ARROW (Anti-Resonant Reflecting Optical Waveguides), visando reduzir as perdas por propagação; e o projeto, fabricação e caracterização de sensores óptico integrados utilizando os processos aprimorados. Os parâmetros estudados foram: os materiais utilizados nas camadas antirresonantes, as espessuras destas camadas, a profundidade de corrosão para definição do rib e a rugosidade nas paredes laterais, que considera-se o parâmetro mais crítico no que diz respeito às perdas por propagação obtidas com o processo de fabricação utilizado neste trabalho. Os materiais utilizados na fabricação dos guias de onda ARROW sobre substrato de silício foram filmes de oxinitreto de silício (SiOxNy) depositados por PECVD à temperatura de 320°C, filmes de SiO2 crescidos em forno de oxidação em ambiente úmido a 1200°C e filmes de TiOxNy depositados pela técnica de Magnetron Sputtering Reativo. A definição das paredes laterais dessas estruturas foi feita através da Corrosão por Plasma Reativo (RIE) e técnicas fotolitográficas convencionais. Para o aprimoramento dos processos, as técnicas de caracterização utilizadas foram: medidas de perdas por propagação, utilizando a técnica de vista superior e a análise modal dos guias de onda. A principal contribuição deste trabalho foi a proposição de um processo de fabricação alternativo, onde pedestais são utilizados para a definição das paredes laterais antes da deposição do núcleo dos guias de onda. Este processo permitiu a redução significativa das perdas e o corte dos modos superiores para guias com larguras menores ou iguais a 6 µm. Finalmente, com os guias e os processos aperfeiçoados foram fabricados dois diferentes tipos de sensores ópticos: sensores refratométricos baseados em interferômetro de Mach-Zehnder (IMZ) e sensores de umidade baseados em absorção utilizando o polímero polipirrol (PPy). A caracterização dos sensores baseados em IMZ permitiu concluir que, embora se tenha observado uma resposta do sensor em termos de variação da potência na saída do dispositivo com a variação do índice de refração, esta variação possivelmente está sendo influenciada pela interferência multimodo resultante de limitações do processo de fabricação, o que reduz significativamente a sensibilidade com relação a valores projetados. Os sensores de umidade apresentaram uma variação significativa da potência de saída para umidades relativas ao redor de 70%, permitindo sua utilização em diferentes aplicações, como na indústria alimentícia e no monitoramento da qualidade do ar. / The main goals of this thesis are: the study and improvement of different geometrical and fabrication process parameters of Anti-Resonant Reflecting Optical Waveguides (ARROWs), aiming at reducing the propagation losses; and the design, fabrication and characterization of integrated optics sensors using the improved processes. The studied parameters were: the materials used as anti-resonant layers, the thickness of these layers, the rib height and the sidewall roughness (SWR), which is considered the most critical parameter with respect to propagation losses in the fabrication process used in this work. The materials used in the fabrication of ARROW waveguides over silicon substrate were silicon oxynitride (SiOxNy) films deposited by PECVD at 320°C, SiO2 films, thermally grown at 1200°C and TiOxNy films deposited by the reactive magnetron sputtering technique. The definition of the sidewalls of these waveguides was performed by Reactive Ion Etching (RIE) and conventional photolithographic techniques. The characterization techniques used were: propagation loss measurements, using the top view technique and modal analysis. The main contribution of this work was the proposition of an alternative fabrication process where pedestals are used in order to define the sidewalls before deposition of the core of the ARROW waveguides. This process allowed significant reduction of losses and cutoff of higher modes at widths of 6 µm. Finally, with the waveguides and improved processes two different types of optical sensors were fabricated: refractometric sensors based on Mach-Zehnder interferometer (IMZ) and humidity sensors based on evanescent field absorption using polypyrrole polymer (PPy). The characterization results of IMZ based sensors showed that, although a sensor response has been observed in terms of change of output power with variation of the external medium\'s refractive index, this variation is possibly being influenced by multimode interference resulting from limitations in the fabrication process. This significantly reduces the sensitivity with respect to designed values. The humidity sensors show a significant variation in output power for relative humidity values around 70%, allowing its use in different applications, such as in food industry and in air quality monitoring.

Orientador: Jose Alexandre Diniz / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-21T20:16:28Z (GMT). No. of bitstreams: 1 Biasotto_Cleber_D.pdf: 3795677 bytes, checksum: e4e2355f73ec8fb2ad7677cdf17f5daf (MD5) Previous issue date: 2012 / Resumo: Atualmente para atender à necessidade de fabricação dos sensores, dispositivos eletrônicos e circuitos integrados com dimensões micro e nanométricas, novos processo de custos e de thermal budgets reduzidos são necessários. Este trabalho apresenta o desenvolvimento de alguns destes novos processos alternativos para aplicação nesta fabricação. O trabalho está dividido em quatro partes: a primeira parte apresenta a obtenção e a caracterização de filmes isolantes de nitreto de silício para aplicação em microsensores, tais como o sensor de pressão. Estes filmes foram obtidos sobre substratos de Si em baixa temperatura (20°C) utilizando-se um reator de plasma do tipo ECRCVD (Electron Cyclotron Resonance - Chemical Vapor Deposition). Normalmente reatores do tipo Low Pressure Chemical Vapor Deposition (LPCVD) ou Plasma Enhanced - CVD (PECVD) em temperaturas maiores que 600ºC e 250ºC, respectivamente, são utilizados para essa aplicação. A caracterização dos plasmas ECR, que foram usados para as deposições dos nitretos, e a fabricação de membranas suspensas com estes filmes são apresentadas. A segunda parte apresenta a fabricação e a caracterização de diodos p+-n fabricados em camada de SiGe crescida por LPCVD sobre substrato de Si. Processo este alternativo em substituição aos executados em reatores epitaxiais de alto custo. Na terceira parte deste trabalho, é apresentado o desenvolvimento de processos em baixa temperatura para aplicação em diodos e tecnologia MOS (Metal-Oxide-Semiconductor). São apresentadas a fabricação e a caracterização elétrica dos capacitores MOS, utilizando as tecnologias ALD (Atomic Layer Deposition) e ICP (Inductively Coupled Plasma) para a obtenção em baixa temperatura dos dielétricos high-k de Al2O3 e SiON de porta MOS, respectivamente. Na quarta parte, são apresentadas também, a fabricação e a caracterização elétrica de diodos n+p utilizando a tecnologia de recozimento a laser. O desenvolvimento de capacitores MOS e diodos possibilitou a fabricação (usando processos em baixa temperatura (?400oC)) de n- e p-MISFETs (Metal- Insulator-Semiconductor Field Effect Transistors), como também a fabricação de um protótipo de transistor MOS de alta velocidade baseado em silício germânio chamado D-DotFET (Disposable Dot Field Effect Transistor). Os processos alternativos desenvolvidos nesta tese apresentam um enorme potencial para aplicação nas próximas gerações de dispositivos CMOS (Complementary Metal Oxide Semiconductor) de dimensões sub-22 nm / Abstract: Nowadays, to attend the needs of the fabrication of sensors, electronic devices and integrated circuits with dimensions of micro and nanometrics, new processes of reduced costs and thermal budgets are needed. This work presents the development of some of these alternative processes for this fabrication. This work is divided in four parts: the first part presents the synthesis and characterization of insulating films of silicon nitride for application in microsensors, such as pressure sensors. These films were deposited on Si substrates at low temperature (20°C) using an ECR-CVD (Electron Cyclotron Resonance - Chemical Vapor Deposition) plasma reactor. Normally, Low Pressure Chemical Vapor Deposition (LPCVD) or Plasma Enhanced CVD - (PECVD) reactors are used for this application with high temperature process higher than 600oC and 250oC, respectively. The characterization of ECR plasmas, which were used to get the silicon nitrides, and the fabrication of suspended membranes based on these nitrides are presented. The second part presents the fabrication and the characterization of p+-n silicon germanium (SiGe) diodes fabricated on SiGe layers, which were grown by LPCVD on Si substrate. The grown of SiGe layers by LPCVD is an alternative process to replace the high cost of epitaxial reactors. In the third part of this work is presented the development of low-temperature processes for application in diodes and MOS (Metal-Oxide-Semiconductor) technology. The fabrication at low temperature and electrical characterization of MOS capacitors, using technologies as: ALD (Atomic Layer Deposition) and ICP (Inductively Coupled Plasma) to get the Al2O3 and SiON high-k gate dielectrics of MOS capacitors are presented, respectively. In the four part, the fabrication and electrical characterization of n+-p diodes using the process of laser annealing are presented as well. The development of MOS capacitors and diodes have become feasible the fabrication (using processes at low temperature (? 400oC)) of n- and p-MISFETs (Metal- Insulator -Semiconductor Field Effect Transistors) and also the fabrication of a high speed MOS transistor prototype based on silicon germanium named D-DotFET (Disposable Dot Field Effect Transistor). In conclusion, the alternative processes developed in this thesis have shown to be a huge potential for application in next generations of CMOS (Complementary Metal Oxide Semiconductor) devices with sub- 22 nm dimensions / Doutorado / Eletrônica, Microeletrônica e Optoeletrônica / Doutor em Engenharia Elétrica

Orientador: Elnatan Chagas Ferreira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-20T12:19:42Z (GMT). No. of bitstreams: 1 Dante_Alex_M.pdf: 3529877 bytes, checksum: 4dd1be9e526e3698ffe5df07e12d5b62 (MD5) Previous issue date: 2012 / Resumo: Sensores a fibra óptica utilizando grades de Bragg em fibra (fiber Bragg grating - FBG) estão se tornando cada dia mais importantes, dada a quantidade de aplicações nas quais vêm sendo empregados. Algumas das principais características dos sensores a FBG são: imunidade à interferência eletromagnética (EMI), isolamento elétrico, baixo peso, flexibilidade, e transmissão de informações a longa distância. Eles estão sendo empregados na medida de temperatura, deformação, carga, tensão mecânica e vibração. Estão presentes também em estruturas inteligentes, onde sensores a FBG distribuídos são incorporados à estrutura, permitindo a monitoração em tempo real das condições estruturais de pontes, trilhos ferroviários e aviões. Este trabalho apresenta uma nova técnica de caracterização de FBGs utilizando deconvolução. Nesta técnica, utiliza-se uma FBG sintonizável, cujo perfil de reflexão é bem conhecido, para caracterização de outra FBG, cujo perfil é inicialmente desconhecido. Utilizando placas eletrônicas com componentes de baixo custo, e um software desenvolvido em LabVIEW®, no qual implementamos a deconvolução dos perfis das FBGs, essa técnica permite o levantamento do perfil de reflexão e outros parâmetros, como a largura espectral FWHM (do inglês Full Width at Half Maximum) e o comprimento de onda de Bragg 'lâmbda'B, de uma FBG. Os resultados obtidos tornaram possível a validação da técnica proposta e permitem concluir que ela é robusta e, com refinamentos matemáticos que podem ser implementados no processo de deconvolução, permite a construção de um caracterizador de FBGs preciso e de custo bem inferior a equipamentos disponíveis comercialmente / Abstract: Optical fiber sensors using fiber Bragg gratings (FBG) are becoming increasingly important, given the amount of applications in which they are being used. Some of the most important characteristics of FBGs are: electromagnetic interference (EMI) immunity, light weight, flexibility, and long range information transmission. FBG sensors are being used in the measurement of temperature, deformation, load, strain and vibration. They are also being used in smart structures, where several distributed sensing FBGs are embedded in materials to allow for the real-time monitoring of the structural conditions of bridges, railroad tracks and airplanes. A new technique for the FBGs characterization using deconvolution is presented. In this technique, a tunable FBG, whose reflection spectrum is known, is used to discover another FBGs profile, which is previously unknown. Using low-cost electronic parts and software developed in LabVIEW, which performs the deconvolution of both FBGs spectra, this technique allows the measurement of the FBG reflection spectrum, its FWHM (Full Width at Half Maximum), and the Bragg center wavelength 'lambda'B. The obtained results enables to validate the proposed technique, allowing concluding that it is robust and, if numerical refinement is implemented, it will be possible to build a low-cost FBG characterization device, in comparison with other commercial devices used for this purpose / Mestrado / Eletrônica, Microeletrônica e Optoeletrônica / Mestre em Engenharia Elétrica

[pt] Neste trabalho é realizado um estudo sobre os transistores HEMT. A partir da geometria do dispositivo, espessuras e densidades de dopagem das camadas que compõem a heterojunção, são obtidas expressões analíticas para a característica IXV do componente bem como para o circuito equivalente de pequenos sinais na faixa de microondas. Posteriormente, os principais efeitos ópticos que ocorrem nos HETM´s são discutidos. O objetivo é determinar o comportamento do dispositivo quando este é iluminado com energia óptica. Ênfase especial é dada aos efeitos fotocondutivo e fotovoltaico. Finalmente, duas aplicações práticas explorando os mecanismos citados acima são apresentadas: sintonia óptica de um oscilador de microondas operando em 2 Ghz e controle óptico do ganho de um amplificador de microondas. / [en] In this work a study about HETMs transistors is carried out. Given the geometry of the device, thickness and doping densities of the layers that form the heterojunction, analytical expressions for the component´s IXV characteristics as well as for the small-signal microwave equivalent circuit are obtained. Later, the major photoffects that occur in HETM´s are discussed. The goal is to determine the behaviour of the device under optical illumination. Special emphasis is given for the photovoltaic and photoconductive effects. Finally, two pratical applications exploring the mechanisms cited above are presented: optical tuning of a 2 Ghz HETM oscillator and optical control of gain of a microwave HEMT amplifier.

No description available.

Réalisée entre décembre 2009 et décembre 2012 au sein de STMicroelectronics Crolles dans l’équipe RET (résolution enhancement techniques), et en partenariat avec le laboratoire Hubert Curien Saint Etienne de l’université de Lyon, cette thèse s’intitule "Impact de la modification de la source dans l’utilisation de la méthode de cooptimisation masque source en lithographie optique, et application au nœud technologique 20 nm". Durant cette étude, nous avons pu étudier la technique d’optimisation de la source optique en lithographie, appelée généralement SMO afin de l’appliquer aux problématiques de l’industrie. Une première partie du manuscrit traitant de la lithographie optique permettra de mieux comprendre les problématiques liées à cette étude, en présentant les techniques utilisées. En effet, afin de permettre à la lithographie optique de continuer la miniaturisation des composants de microélectronique, il est nécessaire d’optimiser au maximum de nombreux éléments de la lithographie. La forme de la source optique utilisée n’échappe pas à cette règle et l’utilisation de sources étendues, hors axe et plus ou moins complexe permet aujourd’hui la production des technologies de pointes. Une seconde partie s’attardera plus sur l’optimisation de la source à proprement parler. Dans un premier temps, la théorie de la diffraction sera étudiée afin de permettre une meilleure compréhension du problème. Des simulations et des mesures SEM ou microscope électronique à balayage seront présentées pour montrer l’efficacité de la méthode SMO, de l’anglais "Source Mask Optimization". Cette étude donnant lieu au développement de nouvelles méthodes rapides et innovantes d’optimisation de la source, l’étude prendra soin de présenter des résultats obtenus dans le cadre de cette thèse. Ainsi, la méthode de SMO interne basée sur le phénomène de diffraction et créée durant cette thèse sera présentée dans cette étude et les résultats en découlant seront étudiés. L’application de l’optimisation de la source à des problématiques industrielles sera également présentée à travers différentes applications des solutions proposées. Finalement, un legs de connaissance nécessaire sera effectué par la présentation des différents outils développés durant cette thèse. Une troisième partie concernera l’étude de l’outil Flexray permettant la génération des sources optimisées. La thèse ayant donné lieu à une nouvelle technique de décomposition de la source en polynôme de Zernike, cette techniques sera présentée ici. Elle sera ensuite utilisée pour modéliser la dégradation d’une source, ainsi que pour corréler la différence de source avec la divergence du modèle empirique de simulation. L’étude des sources a été mise en place suivant un aspect industrielle, afin de contrôler l’évolution du scanner de façon rapide. De plus, des simulations peuvent être utilisées pour compléter cette étude. Finalement, une dernière partie traitera de la cooptimisation entre la source et différents éléments tels que le masque et la forme final du motif souhaité. En effet, si la forme initiale du motif souhaité joue un rôle important dans la définition de la source, il est possible de modifier cette dernière, ainsi que la forme du masque en lui appliquant un OPC afin d’obtenir de meilleurs résultats. Ces modifications seront étudiées durant le dernier chapitre / Conducted between December 2009 and December 2012 within the RET (resolution enhancement technology) team at STMicroelectronics Crolles and in partnership with Saint-Etienne laboratory Hubert Curien of the University of Lyon, this thesis entitled "Impact of changing the source while using the source mask optimization technique within optical lithography, and application to 20 nm technology node. ". In this thesis, Alleaume Clovis studied the optimization of the source used in optical lithography, technique usually called SMO (for source mask optimization) and applied the technique to the industry through several problems. The first part of the manuscript describe the optical lithography generalities, in order to allow a better understanding of the issues and the techniques used in this study. Indeed, to allow optical lithography to continue the miniaturization of microelectronic components, it is necessary to optimize many aspects of the lithography. The shape of the light source used is no exception to this rule and the use of extended sources, off-axis and more or less complex now enables the production of advanced technologies. The second part will then focus on the source modification and optimization. In a first step, the diffraction theory will be examined to demonstrate the theoretical interest of the thesis, and to allow a better understanding of the problem. Simulations and SEM measurements will be presented to show the effectiveness of SMO method. As this study gave birth to several innovative source optimization techniques, they will be presented. Thus, the method of internal SMO based on the phenomenon of diffraction and created during this thesis will be presented and the results would be studied. The application of the source optimization to industrial problems will also be presented through different applications. Finally, a legacy of knowledge will be done by presenting the different tools developed during this thesis. A third part will deal with the study of tool which generate the source inside the scanner allowing the use of optimized and complex sources. The thesis has given rise to a new source decomposition technique using Zernike polynomial. It will be used in this study to model the degradation of a source, and for correlating the impact of a source modification due to SMO technique on the empirical model stability. The study of sources has been implemented according to industrial aspect to monitor the scanner with a quick method. In addition to the Zernike decomposition method, simulations can be used to complete this study. The forth chapter of this study will talk about this implementation. Finally, the last part of the study will talk about the co-optimization of the source with several elements, such as the mask OPC and the final shape of the desired pattern. Indeed, if the initial shape of the desired pattern plays an important role in defining the source, it is possible to modify the latter design shape, as well as the shape of the mask in order to optimize both the source and the target shape. These changes will be discussed in the last chapter

Orientador: José Alexandre Diniz / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-18T16:42:08Z (GMT). No. of bitstreams: 1 Lima_LucasPetersenBarbosa_M.pdf: 10518299 bytes, checksum: abe557fa5f682bd296c9fb416948d523 (MD5) Previous issue date: 2011 / Resumo: Filmes de nitreto de titânio (TiN) e nitreto de tântalo (TaN) foram depositados sobre substratos de Si (100) utilizando um sistema de sputtering reativo, com diferentes fluxos de N2 (10-80 sccm) e potência (500-1500W), em ambiente de N2/Ar. Foram analisadas as influências da mistura gasosa N2/Ar e potência nas propriedades estruturais e elétricas dos filmes de TiN e TaN, utilizando as técnicas de perfilometria, microscopia de força atômica, 4 pontas, espectroscopia Raman, difração de raios-x e espectroscopia de fotoelétron. As análises físicas e elétricas dos filmes de TiN e TaN demonstram que os filmes são policristalinos, com as orientações preferenciais (311)-( 111) e (200)-( 111), respectivamente. Os valores das taxas de deposições, resistividades elétricas e tamanho de grão para os filmes de TiN e TaN estão entre 4 e 78 nm/min, 150 e 7500 ??.cm e 0,001 e 0,027 ?m2, respectivamente. Foram fabricados capacitores MOS e diodos Schottky com eletrodos superiores de TiN e TaN com dielétricos de SiOxNy ou SiO2, e extraídas curvas CV e IV destes dispositivos, para extração de parâmetros como tensão de flatband (VFB), densidade de carga efetiva (Q0/q) e função trabalho do eletrodo superior (WF). As curvas CV dos capacitores MOS com dielétrico de SiOxNy e eletrodo superior de TiN apresentaram valores extraídos de Q0/q, VFB e WF de 1010 cm2, 0,29 V e 4,65 eV, respectivamente, que são compatíveis com a tecnologia CMOS. As curvas CV dos capacitores MOS com dielétrico de SiOxNy e eletrodo superior de TaN apresentaram valores extraídos de Q0/q, VFB e WF de 1010 cm2, 1,36 V e 3,81 eV, respectivamente, que não são compatíveis com a tecnologia CMOS. As curvas CV dos capacitores MOS com dielétrico de SiO2 e eletrodo superior de TiN apresentaram valores extraídos de Q0/q, VFB e WF de 1010 e 1012 cm2, de 0,12 V e 0,36 V, e, 4,15 eV e 4,43 eV, respectivamente, que são compatíveis com a tecnologia CMOS. As curvas CV dos capacitores MOS com dielétrico de SiO2 e eletrodo superior de TaN apresentaram valores extraídos de Q0/q, VFB e WF de 1010 e 1012 cm2, 0,29 V e 0,20 V, e, 4,41 eV e 4,44 eV, respectivamente, que são compatíveis com a tecnologia CMOS. Estes resultados indicam que os filmes de TiN e TaN são compatíveis para serem utilizados em dispositivos da tecnologia MOS / Abstract: Tantalum nitride (TaN) and titanium nitride (TiN) films have been obtained by DC sputtering, using different nitrogen flow (10 - 80 sccm) and power (500 - 1500 W), in a nitrogen (N2)/argon (Ar) ambient on Si (100) substrates. The N2/Ar ratio in gas mixture and power effects on structural and electrical properties of TaN and TiN films were investigated by scan profiler (film thickness and deposition rate), atomic force microscopy (rms roughness and grain size), fourprobe technique (electrical resistivity), Raman spectroscopy, x-ray diffraction (crystal orientation) and X-ray photoelectron spectroscopy (film composition). The physical and structural analyses of TiN and TaN films show that TiN and TaN films were polycrystalline, with (311)-( 111) and (200)-( 111) preferred orientation, respectively. The deposition rates, electrical resistivities and grain size values of TiN and TaN films were between 4 and 78 nm/min, 150 and 7500 ??.cm and 0,001-0,027 ?m2, respectively. MOS capacitors and Schottky diodes were fabricated with TiN and TaN as upper electrodes and dielectrics with SiOxNy or SiO2. CV and IV measurements were carried out on these devices and flatband voltage (VFB), effective charge density (Q0/q) and metal gate work function (WF) were extracted from these measurements. The extracted values of Q0/q, VFB e WF 1010 cm2, 0,29 V e 4,65 eV, and these values were extracted from CV curves of MOS capacitors with TiN as gate electrode and SiOxNy as gate dielectric. The extracted values of Q0/q, VFB e WF 1010 cm2, 1,36 V e 3,81 eV, and these values were extracted from CV curves of MOS capacitors with TiN as gate electrode and SiOxNy as gate dielectric. The extracted values of Q0/q, VFB and WF were about 1010 and 1012 cm2, 0,12 V and 0,36V, and 4,15 eV and 4,43 eV, and these values were extracted from CV curves of MOS capacitors with TiN as gate electrode and SiO2 as gate dielectric. The extracted values of Q0/q, VFB and WF were about 1010 and 1012 cm2, 0,29 V and 0,20V, and 4,41 eV and 4,44 eV, and these values were extracted from CV curves of MOS capacitors with TaN as gate electrode and SiO2 as gate dielectric. These extracted values for VFB and WF indicates that the TiN and TaN films are suitable for MOS technology / Mestrado / Eletrônica, Microeletrônica e Optoeletrônica / Mestre em Engenharia Elétrica

abstract: Deformable heat exchangers could provide a multitude of previously untapped advantages ranging from adaptable performance via macroscale, dynamic shape change (akin to dilation/constriction seen in blood vessels) to enhanced heat transfer at thermal interfaces through microscale, surface deformations. So far, making deformable, ‘soft heat exchangers’ (SHXs) has been limited by the low thermal conductivity of materials with suitable mechanical properties. The recent introduction of liquid-metal embedded elastomers by Bartlett et al1 has addressed this need. Specifically, by remaining soft and stretchable despite the addition of filler, these thermally conductive composites provide an ideal material for the new class of “soft thermal systems”, which is introduced in this work. Understanding such thermal systems will be a key element in enabling technology that require high levels of stretchability, such as thermoregulatory garments, soft electronics, wearable electronics, and high-powered robotics. Shape change inherent to SHX operation has the potential to violate many conventional assumptions used in HX design and thus requires the development of new theoretical approaches to predict performance. To create a basis for understanding these devices, this work highlights two sequential studies. First, the effects of transitioning to a surface deformable, SHX under steady state static conditions in the setting of a liquid cooling device for thermoregulation, electronics and robotics applications was explored. In this study, a thermomechanical model was built and validated to predict the thermal performance and a system wide analysis to optimize such devices was carried out. Second, from a more fundamental perspective, the effects of SHXs undergoing transient shape deformation during operation was explored. A phase shift phenomenon in cooling performance dependent on stretch rate, stretch extent and thermal diffusivity was discovered and explained. With the use of a time scale analysis, the extent of quasi-static assumption viability in modeling such systems was quantified and multiple shape modulation regime limits were defined. Finally, nuance considerations and future work of using liquid metal-silicone composites in SHXs were discussed. / Dissertation/Thesis / Doctoral Dissertation Engineering 2020

Les matériaux ferroélectriques sont de bons candidats pour réaliser des microdispositifs photostrictifs, capables de se déformer mécaniquement sous éclairement. En effet, lorsqu’ils sont soumis à un rayonnement d’énergie supérieure à leur bande interdite, les charges photoinduites sont séparées par le champ électrique interne du matériau qui dépend de sa polarisation rémanente. Cette séparation de charges génère alors une modification photoinduite du champ électrique et par conséquent une déformation puisque le matériau ferroélectrique est aussi piézoélectrique. Dans cette thèse, le matériau ferroélectrique Pb(ZrₓTi₁₋ₓ)O₃ (PZT) a été choisi pour son coefficient piézoélectrique important. Des couches minces de PZT de haute qualité cristalline ont été déposées par ablation laser pulsé (PLD), et intégrées dans une géométrie capacitive, entre deux électrodes afin de contrôler électriquement les propriétés du matériau. Dans un premier temps, les propriétés piézoélectriques, diélectriques, ferroélectriques et de conduction électrique des couches minces de PZT ont été étudiées et ont montré l’influence des interfaces électrode/ferroélectrique. Les propriétés photovoltaïques des couches minces ont ensuite été étudiées, en fonction de la longueur d’onde d’excitation et de l’état de polarisation, et les résultats obtenus ont démontré l’importance de l’ingénierie sur les réponses photoinduites dans le PZT, notamment le choix de l’électrode supérieure et de la longueur d’onde d’excitation. Le choix de l’électrode supérieure s’est en effet révélé très important pour contrôler le signe des courants et tensions photoinduites ainsi que leur stabilité temporelle. Finalement, les déformations photoinduites dans des films minces de PZT après une impulsion UV ont été étudiées par diffraction des rayons X résolue en temps. L’une des avancées les plus importante de ces travaux réside dans le contrôle in situ de la photostriction (à la fois du signe et de l’amplitude des déformations photoinduites) en faisant varier l’état de polarisation. En considérant les différentes contributions intervenant dans le champ électrique total dans la couche mince, un modèle a été proposé pour expliquer le rôle de la polarisation dans la photostriction. Pour aller plus loin dans l’étude et le contrôle de la photostriction et son optimisation, plusieurs approches ont été explorées, comme la modification de la polarisation rémanente, de la longueur de pénétration des UV, de la fréquence d’excitation UV ou de l’interface électrode/PZT, qui ont montré des effets plus ou moins forts sur la dynamique et l’amplitude de la réponse photostrictive. / Ferroelectric materials are good candidates for photostrictive actuators that deform under illumination. When illuminated above the bandgap energy, photoinduced charges will be separated by the internal electric field of the material, which depends on its remnant polarization. This separation leads to both a photoinduced modification of the electric field and a deformation since a ferroelectric material is also piezoelectric. In this thesis, the ferroelectric material Pb(ZrₓTi₁₋ₓ)O₃ (PZT) was chosen for its high piezoelectric coefficient. PZT thin films of high crystalline quality were grown by pulsed laser deposition (PLD), and integrated in a capacitance geometry between two metallic electrodes to enable the control of the material properties. First, the ferroelectric, dielectric and transport properties were studied to determine the influence of the electrode/ferroelectric interface. The photovoltaic behavior of PZT thin films was subsequently investigated, specifically its dependence on the incident wavelength and the polarization state. The results show that photoinduced response in PZT can be engineered. The choice of the electrodes and the incident energy were found to be particularly important in controlling the sign of the photoinduced current and voltage as well as the temporal stability of the device. Finally, the photoinduced deformation of a PZT thin film after a UV was studied by time-resolved X-ray diffraction. The novelty of this work comes from the in-situ control of the photostriction (both in sign and amplitude) by manipulating the polarization state. By considering the competition between the different components of the total electric field present in the sample, a model was proposed to determine the polarization’s contribution on the photostriction. In order to further control and optimize the photoinduced strain in devices, various approaches were studied, such as tuning the remnant polarization, the UV depth penetration and UV pulses frequency, and developing asymmetric electrodes, and all these approaches were found to affect dynamics and amplitude of photostriction.

2D semiconductors are one of the most promising materials for next-generation electronics. Realizing continuous 2D monolayer semiconductors with single-crystalline structure at the wafer scale is still a challenge. We developed an epitaxial phase conversion (EPC) process to meet these requirements. The EPC process is a two-step process, where the sulfurization process was carried out on pre-deposited Mo-containing films. Traditionally, two-step processes for 2D MoS2 and other chalcogenides have suffered low-quality film and non-discontinuity at monolayer thickness. The reason was regarded as the low lattice quality of precursor film. The EPC process solves these problems by carefully preparing the precursor film and carefully controlling the sulfurization process. The precursor film in the EPC process is epitaxial MoO2 grown on 2″ diameter sapphire substrate by pulsed laser deposition. This epitaxial precursor contains significantly fewer defects compared to amorphous precursor films. Thus fewer defects are inherited by the EPC MoS2 film. Therefore, EPC MoS2 film quality is much better. The EPC prepared monolayer MoS2 devices to show field-effect mobility between 10 ~ 30 cm2·V-1s-1, which is the best among the two-step process. We also developed a CLAP method further to reduce the defects in the precursor oxide film; thus, in-plane texture in the thicker MoS2 film was eliminated, and a single-crystalline structure was obtained in the wafer-scale MoS2 films. The potentially feasible technique to further improve the 2D film quality is pointed out for our next research plan. Meanwhile, the epitaxial phase conversion process was proposed to be as a universal growth method. Last but not least, we demonstrate several potential applications of the wafer-scale single-crystalline MoS2 film we developed, such as logic circuits, flexible electronics, and seeding layer of van der Waal or remote epitaxial growth.