Congenital heart defects are the number one cause of birth defect-related deaths. Cardiovascular diseases are the most common cause of death worldwide. Layered cellular sheet constructs offer one very valuable option for cardiac patch implantation during surgical treatment of both pediatric and adult patients with cardiac defects or damage. A very exciting, relatively unexplored, autologous, available cell source for making patches are placenta-derived mesenchymal stem cells (pMSCs). In this study, pMSCs were assessed as a potential cell source for cardiac repair and regeneration by evaluating their differentiation capacity into cardiomyocytes, their effects on cardiac cell migration and proliferation, and their ability to be grown into cell sheets. It was found that pMSC cardiac protein content was enhanced by differentiation media treatment, but no beating cells were produced. Undifferentiated pMSCs improved migration and proliferation of a cardiac cell population and formed intact, aligned cell sheets. However, like many new cell sources for cardiac repair, pMSCs should still be functionally characterized to understand how compatible they will be with resident heart tissue. Implanting non-autologous, potentially pluripotent, non-myocyte (non-beating) cells presents concerns regarding electromechanical mismatch and implant rejection. The characterization of non-traditional cell sources such as pMSCs motivated the design of a bio-MEMS device that assesses contractile force and conduction velocity in response to electrical and mechanical stimulation of a cell source as it is grown and once it forms a cellular sheet. This ideally creates the ability for patient specific cell sheets to be cultured, characterized, and conditioned to be compatible with the patient’s cardiac environment in vitro, prior to implantation. In this work, the device was designed to achieve the following: cellular alignment, electrical stimulation, mechanical stimulation, conduction velocity readout, contraction force readout, and upon characterization, cell sheet release. The platform is based on a set of comb electrical contacts which are three dimensional wall contacts made of polydimethylsiloxane and coated with electrically conductive metals. Device fabrication and initial validation experiments were completed as part of this study; ultimately the device will allow for the complete functional characterization and conditioning of variable cell source cell sheet implants for myocardial implantation. / 2019-07-02T00:00:00Z

The context of this PhD is the reduction of sizes involved in material development and the confinement of heat in modern devices, which are known to lead to the apparition of hot spots. The goal is to investigate heat conduction from micro- to nanoscale wide Joule-heated wires standing on flat layered materials. A particular focus is given to the analysis of phonon heat dissipation when departing from the well-known Fourier diffusive conduction and entering the ballistic regime. The manuscript starts with a summary of the main observed effects on the effective thermal conductivity in nanoscale materials, especially in light of the values of thermallyaveraged phonon mean free paths and the associated Knudsen number. Then the advantages and drawbacks of various measurement techniques are discussed. The analysis of the experimental configuration requires 2D analytical and 3D finite-element method based numerical studies of diffusive heat conduction from a finite source into a medium. Limitations of the 3! method due to wire length, substrate geometry and thin oxide layers are highlighted. The electro-thermal setup developed and the procedure used to deposit the devices on top of the samples are then detailed. A set of well-known materials with mean free path ranging from few nanometers to hundreds of nanometers is characterized with microwires. The thermal conduction properties of multilayer materials are investigated. Heat dissipation from finite sources on top of silicon substrates is then measured as a function of temperature. The mean free path is known to become large when temperature decreases. As a result, this configuration provides clues for understanding heat conduction from ballistic sources. The observed behavior is very different from the one predicted by Fourier’s law and shows a strong reduction of the dissipation. It is found that the results are comparable to earlier measurements involving ridges. They are analyzed with various levels of approximations of predictions using the Boltzmann transport equation. The results obtained may be useful in many fields, in particular for electronics and thermoelectric designs. / Le contexte de ce doctorat est la réduction des tailles impliquées dans le développement des matériaux et le confinement de la chaleur dans les dispositifs modernes, qui sont connus pour conduire à l'apparition de points chauds. L'objectif est d'étudier la conduction de la chaleur à partir de fils chauffés par Joule à l'échelle nanométrique et à l'échelle nanométrique, reposant sur des matériaux à couches planes. Une attention particulière est accordée à l'analyse de la dissipation thermique des phonons en partant de la conduction de Fourier bien connue et en entrant dans le régime balistique. Le manuscrit commence par un résumé des principaux effets observés sur la conductivité thermique effective dans les matériaux à l'échelle nanométrique, en particulier à la lumière des valeurs des voies libres moyennes des phonons et du nombre de Knudsen associé. Ensuite, les avantages et les inconvénients des différentes techniques de mesure sont discutés. L'analyse de la configuration expérimentale nécessite des études numériques 2D basées sur la méthode des éléments finis et des éléments finis de la conduction de chaleur par diffusion à partir d'une source finie dans un milieu. Limitations du 3! méthode en raison de la longueur du fil, de la géométrie du substrat et des couches minces d'oxyde sont mises en évidence. La configuration électro-thermique développée et la procédure utilisée pour déposer les dispositifs sur les échantillons sont ensuite détaillées. Un ensemble de matériaux bien connus avec un chemin libre moyen allant de quelques nanomètres à des centaines de nanomètres est caractérisé par des microfils. Les propriétés de conduction thermique des matériaux multicouches sont étudiées. La dissipation thermique des sources finies sur les substrats de silicium est ensuite mesurée en fonction de la température. Le libre parcours moyen est connu pour devenir important lorsque la température diminue. En conséquence, cette configuration fournit des indices pour comprendre la conduction de la chaleur à partir de sources balistiques. Le comportement observé est très différent de celui prédit par la loi de Fourier et montre une forte réduction de la dissipation. On trouve que les résultats sont comparables à des mesures antérieures impliquant des crêtes. Ils sont analysés avec différents niveaux d'approximations de prédictions en utilisant l'équation de transport de Boltzmann. Les résultats obtenus peuvent être utiles dans de nombreux domaines, en particulier pour les conceptions électroniques et thermoélectriques.

abstract: This thesis discusses the evolution of conduction mechanism in the silver (Ag) on zinc oxide (ZnO) thin film system with respect to the Ag morphology. As a plausible substitute for indium tin oxide (ITO), TCO/Metal/TCO (TMT) structure has received a lot of attentions as a prospective ITO substitute due to its low resistivity and desirable transmittance. However, the detailed conduction mechanism is not fully understood. In an attempt to investigate the conduction mechanism of the ZnO/Ag/ZnO thin film system with respect to the Ag microstructure, the top ZnO layer is removed, which offers a better view of Ag morphology by using scanning electron microscopy (SEM). With 2 nm thick Ag layer, it is seen that the Ag forms discrete islands with small islands size (r), but large separation (s); also the effective resistivity of the system is extremely high. This regime is designated as dielectric zone. In this regime, thermionic emission and activated tunneling conduction mechanisms are considered. Based on simulations, when "s" was beyond 6 nm, thermionic emission dominates; with "s" less than 6 nm, activated tunneling is the dominating mechanism. As the Ag thickness increases, the individual islands coalesce and Ag clusters are formed. At certain Ag thickness, there are one or several Ag clusters that percolate the ZnO film, and the effective resistivity of the system exhibits a tremendous drop simultaneously, because the conducting electrons do not need to overcome huge ZnO barrier to transport. This is recognized as percolation zone. As the Ag thickness grows, Ag film becomes more continuous and there are no individual islands left on the surface. The effective resistivity decreases and is comparable to the characteristics of metallic materials, so this regime is categorized as metallic zone. The simulation of the Ag thin film resistivity is performed in terms of Ag thickness, and the experimental data fits the simulation well, which supports the proposed models. Hall measurement and four point probe measurement are carried out to characterize the electrical properties of the thin film system. / Dissertation/Thesis / M.S. Materials Science and Engineering 2012

Orientador: Norma Sueli Pinheiro Modolo / Coorientador: Regina Paolucci El Dib / Banca: Eliana Marisa Ganem / Banca: Lais Helena Navarro e Lima / Banca: Eneida Maria Vieira / Banca: José Fernando Amaral Meletti / Resumo: Introdução: acredita-se que a anestesia regional guiada por ultrassonografia (USG) pode melhorar a eficácia dos bloqueios de nervos periféricos e reduzir as complicações na população pediátrica, porém essa hipótese ainda não foi previamente testada de forma quantitativa. Objetivo: a proposta desta revisão sistemática de ensaios clínicos randomizados (ECR) foi avaliar se o uso da ultrassonografia em pediatria melhoraria a taxa de sucesso dos bloqueios e reduziria o índice de complicações comparativamente a outros métodos tradicionais de localização de nervos. Métodos: a pesquisa sistemática, extração dos dados, avaliação crítica e análise conjunta dos dados seguiram as recomendações para a realização de revisões sistemáticas propostas pela Colaboração Cochrane e pela declaração PRISMA. A estratégia de busca incluiu as bases CENTRAL, EMBASE, Medline e Lilacs. A última pesquisa foi realizada em novembro de 2014. O risco relativo (RR) e a diferença média (DM), com seus respectivos intervalos de confiança de 95% (IC 95%), foram calculados utilizando-se o programa estatístico Revman para dados dicotômicos e contínuos, respectivamente. Resultados: onze ensaios clínicos randomizados, publicados entre 2004 e 2013, perfazendo um total de 634 pacientes, cumpriram os critérios de inclusão. A qualidade metodológica foi considerada moderada. Houve um pequeno benefício da ultrassonografia na taxa de sucesso (RR 1,19; IC 95% 1,07-1,32) que foi variável de acordo com a região anatômica avaliada, associado a uma redução na necessidade de analgesia no pós-operatório com o uso da ultrassonografia (RR 0,2; IC 95% 0,11-0,34). Apenas uma complicação foi reportada nos estudos incluídos. Uma punção vascular em um paciente do grupo controle durante realização do bloqueio ílio-inguinal/ílio-hipogástrico (II/IH). Conclusão: existe moderada evidência de que a ultrassonografia quando utilizada para... / Abstract: Background: it has been suggested that ultrasound-guided regional anesthesia could improve the blockade efficacy and decrease complication rates in the pediatric population, but this hypothesis has not previously been adequately tested in a quantitative manner. Aim: the purpose of this systematic review of randomized clinical trials (RCT) is to assess whether the use of ultrasonography in the pediatric population has advantages over any other method of nerve location, such as the anatomical landmark-based technique, paraesthesia or use of an electrical nerve stimulator. Methods: the systematic search, data extraction, critical appraisal and pooled analysis were performed according to the Cochrane Handbook and PRISMA guidelines. The search strategy included the CENTRAL of the Cochrane Library, Medline, EMBASE, and Lilacs. The date of the last search was November 5, 2014. The relative risk (RR), mean difference (MD) and their corresponding 95% confidence intervals (95% CIs) were calculated using the Revman statistical software for dichotomous and continuous outcomes, respectively. Results: eleven randomized, clinical, controlled trials (published between 2004 and 2013) with a total 634 patients met the inclusion criteria. The methodological quality of the included studies was considered regular. There was a slight benefit of ultrasound to the success rate (RR 1.19, 95% CI 1.07 to 1.33), which was variable according to the anatomical region studied and a more important reduction of the analgesia requirement in the postoperative period with the use of ultrasound for peripheral nerve blocks (RR 0.2, 95% CI 0.11-0.34). There was only one complication reported (blood vessel puncture in one control group). Conclusions: there is moderate evidence that the use of ultrasound-guided peripheral nerve block in children reduces the number of patients requiring additional analgesia in the postoperative period and ... / Doutor

Neste trabalho apresenta-se uma discussão geral sobre problemas inversos, problemas mal-postos c técnicas de regularização, visando sua aplicabilidade em problemas térmicos. Métodos numéricos especiais são discutidos para a solução de problemas que apresentam instabilidade em relação aos dados. Tais métodos baseiam-se na utilização de restrições ou informações adicionais sobre a solução procurada. O problema de determinação da condição inicial da equação do calor é resolvido numericamente através destas técnicas, particularmente a regularização de Tikhonov e o príncipio da máxima entropia conectados ao príncipio da discrepância de Morozov são utilizados. / In this work we present a general discussion on invcrse problems, ill-posed problems and regularization techniqucs, applying these techniques to thermal problcms. Special numerical methods are discusscd in order to solve problerns for which the solution is unstable under data perturbations. Such methods are based on the utilization of restrictions or additional information on thc solution. The problern of determining the initial condition of thc heat equation is numerically solved beyond thesc techniques, particularly thc T ikhonov regularization and thc maximum entropy principie connected to thc Morozov's discrepancy principie are used.

O presente trabalho trata da modelagem da condução de calor transiente com geração de calor em meios heterogêneos, e tem o objetivo de desenvolver um modelo multiescala adequado a esse fenômeno. Já existem modelos multiescala na literatura relacionados ao problema proposto, e que são válidos para os seguintes casos: (a) o elemento de volume representativo tem tamanho desprezível quando comparado ao comprimento característico macroscópico (e como consequência, a microescala tem inércia térmica desprezível); ou (b) a geração de calor é homogênea na microescala. Por outro lado, o modelo proposto nesta tese, o qual é desenvolvido utilizando uma descrição variacional do problema, pode ser aplicado a elementos de volume representativos finitos e em condições em que a geração de calor é heterogênea na microescala. A discretização temporal (diferenças finitas) e as discretizações espaciais na microescala e na macroescala (método dos elementos finitos) são apresentadas em detalhes, juntamente com os algoritmos necessários para implementar a solução do problema. Nesta tese são apresentados casos numéricos simples, procurando verificar não só o modelo teórico multiescala desenvolvido, mas também a implementação feita. Para tanto, são analisados, por exemplo, (a) casos em que considera-se a microescala um material homogêneo, tornando possível a comparação da solução multiescala com a solução convencional (uma única escala) pelo método dos elementos finitos, e (b) um caso em um material heterogêneo para o qual a solução completa, isto é, modelando diretamente os constituintes no corpo macroscópico, é obtida, tornando possível a comparação com a solução multiescala. A solução na microescala para vários casos analisados nesta tese sofre grande influência da inércia térmica da microescala. Para demonstrar o potencial de aplicação do modelo multiescala, simula-se a cura de um elastômero carregado com negro de fumo. Embora a simulação demonstre que a inércia térmica não precise ser considerada para esse caso em particular, a aplicação da presente metodologia torna possível modelar a cura do elastômero diretamente sobre a microescala, uma abordagem até então não utilizada no contexto de métodos multiescala. Essa metodologia abre a possibilidade para futuros aperfeiçoamentos da modelagem do estado de cura. / This work deals with the modeling of transient heat conduction with heat generation in heterogeneous media, and its objective is to develop a proper multiscale model for this phenomenon. There already exist multiscale models in the literature related to this proposed problem, and which are valid for the following cases: (a) the representative volume element has a negligible size when compared to the characteristic macroscopic size (and, as a consequence, the microscale has a negligible thermal inertia); or (b) the heat generation is homogeneous at the microscale. On the other hand, the model proposed in this thesis, which is developed using a variational description of the problem, can be applied to finite representative volume elements and in conditions in which the heat generation is heterogeneous at the microscale. The time discretization (finite difference) and the space discretizations at both the microscale and the macroscale (finite element method) are presented in details, together with the algorithms needed for implementing the solution of the problem. In this thesis, simple numerical cases are presented, aiming to verify not only the theoretical multiscale model developed, but also its implementation. For this, it is analyzed, for instance, (a) cases in which the microscale is taken as a homogeneous material, making it possible the comparison of the multiscale solution with the conventional solution (one single scale) by the finite element method, and (b) a case in a heterogeneous material for which the full solution, that is, modeling all constituents directly on the macroscale, is obtained, making it possible the comparison with the multiscale solution. The solution at the microscale for several cases analyzed in this thesis suffers a large influence of the microscale thermal inertia. To demonstrate the application potential of the multiscale model, the cure of a carbon black loaded elastomer is simulated. Although the simulation shows that the thermal inertia does not have to be considered for this case in particular, the application of the present methodology makes it possible to model the cure of the elastomer directly at the microscale, an approach not used in multiscale methods context until now. This methodology opens the possibility for future improvements of the state of cure modeling.

O presente trabalho utiliza o método Design Construtal para desenvolver o estudo numérico de uma configuração de caminhos de alta condutividade de geometria trifurcada que minimiza a resistência ao fluxo de calor, quando a área do caminho trifurcado é mantida constante. O objetivo deste trabalho é o estudo da influência da geometria sobre o desempenho térmico do sistema bem como a otimização do mesmo, assim obtendo uma configuração que minimiza a resistência térmica para cada condição imposta. São apresentadas as considerações e hipóteses utilizadas para a análise, obtendo a equação do calor regente e as condições de contorno do problema, bem como a função objetivo. Para a solução numérica da equação da condução do calor, é utilizado o software MATLAB ®, especificamente as ferramentas PDETOOL, Partial Differential Equations Tool, e GA, Algoritmo Genético. A resistência térmica é minimizada para cada grau de liberdade. A cada nível de otimização, a influência do grau de liberdade em questão é estudada, obtendo um mapeamento da importância de cada grau de liberdade sobre o sistema trifurcado. Também são obtidas as configurações ótimas para diferentes frações de área. Posteriormente, é estudado o comportamento da configuração ótima do sistema para diferentes temperaturas do final das bifurcações do sistema, mostrando que, para as temperaturas estudadas neste trabalho, a configuração ótima não se altera, apenas a resistência térmica, com a alteração na temperatura do sumidouro direito sendo mais influente sobre essa, seguida do sumidouro central e, por fim, do sumidouro esquerdo. Finalmente, este trabalho mostra, com esses resultados, que a geometria ótima é aquela que melhor distribui as imperfeições do sistema, de acordo com o princípio da ótima distribuição das imperfeições e, também, possui robustez quanto às pequenas imperfeições inseridas no sistema. / The present work employs Constructal Design method to develop a numerical study of a triforked high conductivity pathway that minimizes the heat flow resistance when the triforked pathway area is kept constant. The objective of this work is the study of the influence of the geometry over the thermal performance of the system as well as the optimization of the latter, thus obtaining a configuration that minimizes the thermal resistance for each imposed condition. The considerations and hypothesis for the analysis are shown, obtaining a reigning heat equation and boundary conditions for the system, as well as the objetctive function (minimization of the maximum temperature). For the numerical solution of the heat conduction equation, it is utilized MATLAB ® software, specifically the PDETOOL, Partial Differential Equations Tool, and GA, Genetic Algorithm, toolboxes. The thermal resistance is minimized for every degree of freedom. In each level of optimization, the influence of the degree of freedom in question is studied, obtaining a mapping of the importance of each degree of freedom over the performance of the triforked pathway. Optimal configurations are also obtained for different area fractions. Posteriorly, the behavior of the optimal geometry is studied for different temperatures of the branches of the system. Results show that, for the temperatures studied in this work, the optimal configuration does not change, only the thermal resistance, with the increase of temperature of the right sink being more influential over it, followed by the temperature of the middle sink and, at last, the temperature of the left sink. Finally, this work shows, with these results, that the optimal geometry is the one that better distributes the imperfections of the systems, which is in accordance to the principle of the optimal distribution of imperfections, while possessing a certain robustness over small imperfections inserted in the system.

Submitted by BRENO JOSE HULLE PEREIRA null (brenojhp@hotmail.com) on 2016-04-09T14:37:30Z No. of bitstreams: 1 Qualidade do sono em pacientes com síndrome do túnel do carpo - Pós defesa.pdf: 1149395 bytes, checksum: 10d3bbaef52562ba5ec7284510070c8c (MD5) / Approved for entry into archive by Ana Paula Grisoto (grisotoana@reitoria.unesp.br) on 2016-04-11T13:04:38Z (GMT) No. of bitstreams: 1 pereira_bjh_me_bot.pdf: 1149395 bytes, checksum: 10d3bbaef52562ba5ec7284510070c8c (MD5) / Made available in DSpace on 2016-04-11T13:04:38Z (GMT). No. of bitstreams: 1 pereira_bjh_me_bot.pdf: 1149395 bytes, checksum: 10d3bbaef52562ba5ec7284510070c8c (MD5) Previous issue date: 2016-03-02 / Frequentemente os sintomas da síndrome do túnel do carpo (STC) ocorrem à noite, mas a relação entre STC e características do sono destes pacientes ainda não foram sistematicamente investigadas através de métodos objetivos, tais como a eletroneuromiografia (ENMG) e a polissonografia (PSNG), o que constitui o objetivo deste estudo. Métodos: Pacientes do sexo feminino com STC, diagnosticadas por estudo de condução nervosa (ENMG), foram estudadas por exames de polissonografia e listadas de acordo com a gravidade da STC, mensurada pela latência motora distal (LMD) do nervo mediano da mão ou mãos afetadas, e seus dados polissonográficos foram analisados. Resultados: 42 pacientes foram estudadas de Junho de 2011 a Junho de 2015. O Índice de Despertares (ID) das pacientes com STC acentuada mostrou-se alterado em uma porcentagem maior do que nas pacientes com STC leve ou moderada (100, 60 e 66%, respectivamente). Essa relação de prevalência se manteve quando o Tempo de Dessaturação (TD) foi analisado. Alterações da Eficiência do Sono (ES) foram mais comuns em pacientes com STC bilateral. Arquitetura do sono está igualmente alterada em todos os pacientes, com sono de ondas lentas (N3) e sono REM diminuídos em todos os grupos. A presença de Síndrome da Apneia Obstrutiva do Sono (SAOS) não dependeu da gravidade da STC. Conclusões: Quanto mais grave a STC documentada por ENMG, mais prevalente é o sono fragmentado e a dessaturação do sono. No entanto, analise aprofundada é necessária para se estabelecer relações entre a qualidade do sono e a gravidade da STC. / Frequently the symptoms of the carpal tunnel syndrome (CTS) occur at night time, but the relation between CTS and the sleep characteristics of those patients have yet to be systematically described by objective methods, such as conduction studies (ENMG) and polysomnography (PSG), which is the aim of this study. Methods: Consecutive female patients with CTS diagnosed by ENMG were studied by polysomnographic exams and listed in accordance with CTS severity, evaluated by distal motor latency of the median nerve of the affected hand or hands, and their polysomnographic data were analysed. Results: 42 patients were studied from June 2011 to June 2015. The Arousal Index (AI) of the patients with severe CTS were altered in larger proportion of those individuals than in those patients with slight or moderate CTS (100, 60% and 66%, respectively). This relation was also prevalent when the Desaturation Time (DT) was analyzed. Alterations of the Sleep Efficiency (SE) were more common among patients with bilateral CTS. Sleep architecture was equally altered among all patients, with slow wave sleep (SWS) and REM sleep diminished in all groups. The presence of Obstructive Sleep Apnea (OSA) was not dependent on CTS severity. Conclusions: The larger the CTS severity evaluated by ENMG, the more prevalent were fragmented sleep and sleep desaturation. Further analysis is required to ascertain causal relations between sleep quality and CTS severity.

Made available in DSpace on 2014-06-11T19:35:41Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-01Bitstream added on 2014-06-13T18:48:27Z : No. of bitstreams: 1 correa_va_dr_guara.pdf: 949805 bytes, checksum: 5d0ebae9cf9395efc83588da395f5ab9 (MD5) / Universidade Estadual Paulista (UNESP) / Com a evolução dos sistemas de computação simbólica ampliou-se a capacidade de modelagem e análise de problemas provenientes de equações diferenciais. Propõe-se a resolução da equação da condução de calor em regimes permanente e transiente para uma geometria cilíndrica com condições de contorno convectivas de forma analítica e numérica utilizando o software de computação simbólica Maple. Para este propósito serão empregados para a resolução analítica, o método de separação de variáveis e para a resolução numérica, o método das diferenças finitas com o esquema Crank- Nicolson e explícito. Os resultados obtidos das resoluções analíticas e numéricas, para algumas situações avaliadas são comparadas. As vantagens computacionais da utilização do software Maple são apresentadas. / The evolution of symbolic computation systems enlarges the capacity of modeling and analysis of problems by differential equations. The aim is the resolution of the conduction heat equation in unsteady and steady state for the cylindrical geometry with convective boundary conditions with analytical and numerical solutions using the Maple software. To this results will be used the separated variables method and finite differences to numerical solutions with Crank-Nicolson and explicit schemes. The results obtained for numerical and analytical solutions for some situations it will available and compared. The computational advantages of the Maple software are showed too.

Cette thèse se propose d'étudier les phénomènes de commutations d'états de résistance dans des structures Métal-Isolant-Métal (MIM) utilisant l'oxyde d'hafnium comme isolant. L'oxyde d'hafnium est un matériau mature de l'industrie de la microélectronique (procédés de dépôts et de mise en forme contrôlés). Les objectifs sont d'élucider les mécanismes à l'origine de ces phénomènes et d'identifier les différents paramètres des empilements MIM influant sur ces phénomènes. Dans l'introduction générale, il est présenté, en détail, le principe de fonctionnement de la commutation d'états résistifs, ainsi qu'une présentation des principales applications potentielles. Cette partie se termine par une brève revue des mécanismes de fonctionnement proposés dans la littérature et par une présentation détaillée des objectifs de la thèse. Les travaux de cette thèse s'articulent autour de deux parties distinctes, chacune composée de trois chapitres. La première partie de ce manuscrit traite principalement de l'étude de la commutation d'états résistifs par des mesures courant-tension (I-V) afin d'identifier l'effet des matériaux constitutifs de l'empilement MIM. Les deux premiers chapitres traitent de l'influence des électrodes supérieures sur les propriétés mémoires. L'influence de la morphologie et du dopage du métal d'électrode, dans le cas d'électrode en or, est présentée dans ce premier chapitre. Dans le deuxième chapitre, l'étude est étendue à différents métaux utilisés comme électrodes supérieures. Le troisième chapitre s'intéresse à suivre l'effet de traitements plasmas post dépôts appliqués à l'oxyde d'hafnium avant métallisation de l'électrode supérieure. La deuxième partie de cette thèse étudie la commutation d'états résistifs par des mesures de courant en fonction du temps (mesures I-t), dans le cas de l'application de tensions constantes. On s'attache plus particulièrement à la cinétique de transitions de résistance. Le premier chapitre de cette partie traite plus spécifiquement d'études I-t réalisées pour de faibles champs électriques afin de caractériser les propriétés des structures MIM avant changement d'état de résistance. Le deuxième chapitre propose une étude visant à modéliser la dégradation de l'oxyde par un modèle cinétique et analytique. Le dernier chapitre propose une caractérisation complémentaire de la transition résistive par des mesures de tension en fonction du temps (mesures V-t), dans le cas de l'application de courants constants. Pour conclure nous rappelons nos principaux résultats et concluons sur les nouveaux éléments de compréhension de la commutation d'états de résistance apportés dans ce manuscrit. / This work deals with resistance switching in HfO2 based Metal-Insulator-Metal (MIM) devices. Hafnium oxide is a widely used material in microelectronics. The goals are to understand physical mechanisms underlying resistance switching phenomena and to identify MIM key parameters which control these phenomena. As a general introduction, the resistance switching principles and potential applications are presented. The different mechanisms proposed in the literature are briefly reviewed and the detailed objectives of this work are described. This work is divided in two parts; each one is composed of three chapters. The first part mainly deals with the study of resistance switching through I-V measurements in order to identify materials effects. The first two chapters study the impact of top electrode material on memory properties. In the first chapter, the influence of metal electrode doping and morphology are presented for the case of gold electrodes. In the second chapter, the study is enlarged to other metals. The third chapter studies the impact of post deposition plasma treatments applied to HfO2 before metallization of the top electrode. In the second part, the resistance switching properties of MIM stacks are studied using I-t measurements under constant voltage stress (CVS). This part focuses on resistance transition kinetics. In the first chapter, low electric field effect is studied to characterize insulating properties before resistance changes. The second chapter provides an analytical kinetic model for resistance degradation. The results presented in the last chapter confirm the model through V-t measurements under constant current stress (CCS). To conclude, key results are summarized and a better understanding of resistance switching is provided.