Dye-sensitized solar cells (DSSCs) have attained considerable attention during the last decade because of the potential of becoming a low cost alternative to silicon based solar cells. Electron transport is one of the prominent processes in the cell and it is further a complex process because the transport medium is a mesoporous film. The gaps in the pores are completely filled by an electrolyte with high ionic strength, resulting in electron-ion interactions. Therefore, the electron transport in these so called state-of-the-art systems has a practical limit because of the low electron diffusion coefficient (Dn) in this mesoporous film photoanode. This work focuses on the influence of the advanced core-shell nanoarchitecture geometry on electron transport and also on the influence of electron-ion interactions. In order to achieve the proposed goals, DSSCs based on ordered, highly aligned, 3D radial core-shell Au-TiO2 hybrid nanowire arrays were fabricated, using three different approaches. J-V, IPCE, and EIS characteristics were studied. The efficiency, light scattering and charge transport properties of the core-shell nanowire based devices were compared to TiO2 nanotube as well as TiO2 mesoporous film based DSSCs. The Au nanowires inside the crystalline TiO2 anatase nanoshell provided a direct conduction path from the TiO2 shell to the TCO substrate and improved transport of electrons between the TiO2 and the TCO. The optical effects were studied by IPCE measurement which demonstrated that Au-TiO2 nanowires showed an improved light harvesting efficiency, including at longer wavelengths where the sensitizer has weak absorption. The metal nanostructures could enhance the absorption in DSSCs by either scattering light enabling a longer optical path-length, localized surface plasmon resonance (LSPR) or by near-field coupling between the surface plasmon polariton (SPP) and the dye excited state. Rapid, radial electron collection is of practical significance because it should allow alternate redox shuttles that show relatively fast electron-interception dynamics to be utilized without significant sacrifice of photocurrent. A combination of improved electron transport and enhanced light harvesting capability make Au-TiO2 core-shell nanowire arrays a promising photoanode nanoarchitecture for improving photovoltaic efficiency while minimizing costs by allowing thinner devices that use less material in their construction.

Au cours de cette thèse, on étudie les systèmes différents : graphène (une monocouche de carbone), graphène fonctionnalisé et les nanofils de Bismuth en induisant la supraconductivité par l’effet proximité. On montre que l’effet proximité fonctionne comme un probe sensible pour les effets des interactions, de couplage spin-orbite, etc.La structure de band de graphène a une relation dispersion linéaire au niveau de Fermi, et le band de conductance et le band de valence est lié aux six points dans l’espace réciproque, appelé le point Dirac. Autour du point Dirac, graphène occupe d’une densité d’état faible (par rapport aux métaux). Alors le niveau de Fermi dans graphene est modulable. On fabrique les jonctions S/Graphene/S avec les contacts de matériaux différents (Al, ReW, Nb). En comparant avec la théorie, on a complété le diagramme du produit R_N I_c (R_N la résistance d’état normal, I_c le courant critique dans une jonction) vs l’énergie Thouless E_Th (une énergie caractéristique intervient dans la jonction SNS longue et dépend la partie normale). Une réduction de R_N I_c globale de la jonction courte à la jonction longue, surtout dans la limite de la jonction longue, la réduction est 10 fois plus grande que celle de la jonction courte. On l’explique par une réduction d’une énergie Thouless effective à cause l’interface S/G imparfaite. Une suppression du supercourant près du point Dirac dans les jonctions longues est considérée comme une signature de la réflexion Andreev spéculaire sur les « puddles » dans le graphène. Aussi, l’injection des paires de Cooper dans les états de bord de l’effet Hall quantique du graphène est étudiée dans cette thèse.L’interaction du couplage spin-orbite et l’effet proximité peut produire les physiques très intéressantes comme le supra de triplet, jonction π, et récemment la formation des Fermions majoranas. Motivé par ces possibilités d’explorer les nouvelles physiques, on a essayé d’induire le couplage spin-orbite dans graphène dans lequel ce couplage est initialement très faible. En greffant les molécules de Pt-porphyrines, qui tiennent un atome de Pt au milieu, on espère que le couplage spin-orbite fort dans l’atome de Pt peut « diffuser » dans le graphène. Au lieu d’avoir vu le couplage spin-orbite, on a plutôt découvert un magnétisme qui dépend la grille dans le graphène induit par les molécules. Plusieurs échantillons avec les contacts normaux ou supraconducteurs sont mesurés avant et après mettant les molécules. Un transfert de charge dans deux sens (électron ou trou) est observé à la température ambiante. Il est lié à l’alignement des niveaux de Fermi des molécules et le graphène. A basse température (~70mK), les hystérésis dans la magnétorésistance (MR) et une asymétrie en B_(//) et B_⊥ impliquent un magnétisme dans graphène. Plus spectaculaire, une asymétrie en la dépendance de la grille du supercurrent est détectée. Bismuth est un élément très lourd et un matériau avec le couplage Rashba spin-orbite fort. On a connecté les nanofils de Bismuth avec tungstène (H_c∼12T) électrodes par FIB (Focused Ions Beam) et induit l’effet proximité dans les fils. Les résultats les plus étonnants sont : (1) le supercourant se tient au champ magnétique jusqu’à 11 Tesla. (2) Il y a des oscillations dans le courant critique en fonction du champ avec une période de centaine gauss qui ressemble à celui d’une structure de SQUID (composé des deux jonctions Josephson en parallèles. (3) Sur ces oscillations, nous trouvons aussi une modulation quasi-périodique lente de quelque milles gauss. Pour expliquer tous ces phénomènes, nous proposons qu’il y a quelques canaux étroites balistiques 1D se forment aux bords des certaines surfaces qui se tiennent au champ jusqu’à 11T et se construisent une interférence entre eux. L’effet Zeeman cause une modulation de phase entre les quasi-particules dans une paire d’Andreev qui module donc le supercourant en échelle de quelques milles gauss. / In this thesis we investigated graphene and Bi nanowire systems by inducing superconducting proximity effect in them. Typically the samples are realized in the form of S/N/S junction. The special properties of these systems are revealed by observing some unusual proximity effect in them. The interplay of the superconducting proximity effect and other effects (spin-orbit coupling, Zeeman effect, quantum Hall effect, impurities, etc...) at the mesoscopic scale gives rise to new physics. Some of our main results are listed below.GrapheneWe succeeded to induce superconducting proximity effect in the very long junction limit, thus completing the diagram of the superconducting proximity effect in graphene. Since by changing the gate voltage, one changes the carrier density in graphene and eventually the transport characteristic quantities (l_e, E_Th etc...). We could scan a whole range of Thouless energy. We present a diagram of eR_N I_c vs Thouless energy compared to theoretical prediction. The Thouless energy dependence of the eR_N I_c products varies from the long junction limit to the short junction limit. The discrepancy (mainly due to the imperfect S/G interface) between theory and experiment is also limit dependent: in the short junction limit, the eR_N I_c products are smaller than the theoretical prediction (with a perfect interface) by a factor of about 3-4; in the long junction limit, however, the disagreement is increased to about 100. We show that the factor deduced from the junctions in different limits is length dependent. This can be explained by the effect of finite transmission at the S/G interface in both the critical current I_c and the induced mini-gap in the graphene. In another hand, a suppression of supercurrent near the Dirac point is observed in long junctions which is attributed to the indication of the specular Andreev reflection upon the puddles in graphene. Also the injection of the Cooper pairs into the QHE edge states is investigated in this thesis.Graphene grafted with Pt-porphyrinsBy grafting the Pt-porphyrins onto graphene, we observed a charge transfer between molecules and the graphene both for electrons and holes. One of the important consequences of the charge transfer is that when the molecules are ionized, a collective magnetic order can be formed by the long range RKKY interaction: the magnetic moments interact via the carrier in graphene. This effect is detected by a hysteretic magnetoresistance of the graphene in a perpendicular field and the asymmetric magnetoresistance in parallel field. Even more striking, the observation of a unipolar supercurrent in S/G/S junction implies that this magnetism induced by porphyrins is gate dependent. The theoretical calculations by Uchoa et al. using the Anderson model indeed find that the gate voltage should tune the impurities in graphene between non-magnetic state and magnetic state.Bi nanowireThe observation of a SQUID-like oscillations persisting up to 10 T and thousands Gauss range modulation in I_c hints to a complex physic in the W-Bi nanowire-W junctions. The results are consistent with a SQUID structure consisting of 2 edges channels which could have an I_c oscillation with period defined by the area between the two edges, typically the size of the nanowire. The origin of the edge states formation is attributed to the strong spin-orbit coupling in Bi that leads to the quantum spin Hall (QSH) state. The thousands Gauss range modulation is the consequence of the interplay between the Zeeman effect and the proximity effect. The phase accumulation in an Andreev quasiparticle pair is Δϕ=g_eff⋅μ_B⋅B_(//) (ℏv_F/L) which is of the order of few thousands Gauss. In one particular sample, a full modulation of the critical current with about 1 T range is observed. This is similar to the proximity effect in S/F/S junctions which suggests a 0-π junction transition.

Les microphones à électret dédiés à l'électronique grand public et les applications médicales (les audioprothèses) ont atteint les limites de la miniaturisation. Depuis la sortie du premier microphone basé sur une technologie microsystème sur silicium (MEMS: Micro-Electro-Mechanical Systems), les microphones à électret sont progressivement remplacés par les microphones MEMS. Les MEMS utilisent le silicium car il offre des caractéristiques mécaniques exceptionnelles avec de bonnes propriétés électriques et la technologie de fabrication est maintenant bien maîtrisée. La plupart des microphones MEMS qui sont décrits dans la littérature sont constitués d’une membrane qui vibre en dehors du plan du capteur, et utilisent la transduction capacitive. La miniaturisation de tels microphones est limitée car leur sensibilité est liée à la valeur de la capacité qui dépend de la taille de la membrane. En outre, les capteurs capacitifs sont très sensibles aux capacités parasites et aux non-linéarités. Cette thèse présente une nouvelle architecture de microphone MEMS qui utilise des micro-poutres qui vibrent dans le plan capteur. La transduction du signal est réalisée par des nanojauges piézorésistives intégrées dans le microsystème et attachées aux micro-poutres. Ce système de détection original ne présente pas les inconvénients de la détection capacitive et à la différence des piézorésistors classiques intégrés dans la membrane de silicium, les nanofils suspendus permettent d’éliminer les courants de fuite. De plus, l'amélioration de la détection est possible puisque le coefficient piézo-résistif longitudinal est inversement proportionnel à la section du nanofil. Les fluctuations de pression acoustique entraînent les déviations des micro-poutres qui produisent une concentration de contraintes dans les nanogauges. Le comportement du capteur, que l’on cherche à modéliser, est lié à des phénomènes mécaniques, acoustiques et électriques qui sont couplés. En raison des dimensions micrométriques du MEMS, les effets des dissipations thermique et visqueuse doivent être pris en compte dans le comportement acoustique. Pour prédire de façon fiable le comportement du capteur, deux modèles vibroacoustiques sont utilisés: un modèle éléments finis basé sur l'ensemble des équations de Navier-Stokes linéarisées et un modèle approché basé sur un schéma à constantes localisées (représentation par circuit électrique équivalent). Les deux modèles sont complémentaires dans le processus de conception pour déterminer la réponse en fréquence et le taux de bruit du capteur. Le travail est complété par la description des processus technologiques et les défis liés à la fabrication du prototype. Puis deux approches pour la caractérisation fonctionnelle du microphone MEMS sont présentées, la première en tube d’impédance, la seconde en champ libre. / Electret microphones dedicated to consumer electronics and medical applications (hearing aids) have reached the miniaturization limits. Since the release of the first microphone based on Silicon micromachining, electret microphones are constantly replaced by MEMS microphones. MEMS (Micro-Electro-Mechanical Systems) microphones use Silicon that provides exceptional mechanical characteristics along with good electric properties and mature fabrication technology. Regardless of the transduction principle (capacitive, piezoresistive, piezoelectric, optical), all of the MEMS microphones reported in the state of the art literature are based on a membrane deflecting out of the plane of the base wafer. Most of the reported microphones and all of the commercially available MEMS use capacitive transduction. Downscaling of capacitive microphones is problematic, since the sensitivity depends on capacitance value. Moreover capacitive sensors suffer of high sensitivity to parasitic capacitance and nonlinearity. The drawbacks of capacitive detection may be overcome with use of piezoresistive properties of Silicon nanowires. Unlike the classical piezoresistors integrated into silicon membrane, suspended nanowires do not suffer of leakage current. Further improvement of piezoresistive detection is possible since the longitudinal piezoresistive coefficient rises inversely proportional to nanowire section. This thesis presents the considerations of novel MEMS microphone architecture that uses microbeams which deflect in the plane of the base wafer. Signal transduction is achieved by piezoresistive nanogauges integrated in the microsystem and attached to the microbeams. Acoustic pressure fluctuations lead to the deflection of the microbeams which produces a stress concentration in the nanogauges. Accurate simulations of the discussed transducer couple acoustic, mechanical and electric behavior of the system. Due to micrometric dimensions of the MEMS acoustic system, thermal and viscous dissipative effects have to be taken into account. To reliably predict the sensor behavior two acoustic models are prepared: the complete Finite Element Model based on the full set of linearized Navier-Stokes equations and the approximative model based on the Lumped Elements (Equivalent Cirtuit Representation). Both models are complementary in the design process to finally retrieve the frequency response and the noise budget of the sensor. The work is completed by the description of the technological process and the challenges related to the prototype microfabrication. Then the approach to the MEMS microphone characterization in pressure-field and free-field is presented.

Neste trabalho é apresentado um estudo dos transistores MOS sem junções (Junctionless Nanowire Transistors - JNTs), cujo foco é a modelagem de suas características elétricas e a análise do funcionamento dos mesmos quanto à tensão de limiar, ponto invariante com a temperatura e operação analógica. Os JNTs possuem uma concentração de dopantes constante da fonte ao dreno sem apresentar gradientes. Eles foram desenvolvidos a fim de se evitar as implantações iônicas de fonte e dreno, que requerem condições rigorosamente controladas para se evitar a difusão de dopantes para o interior do canal em dispositivos de tamanho extremamente reduzido (sub-20 nm). Dessa forma, esses dispositivos permitem um maior escalamento, com um processo de fabricação simplificado. Os trabalhos recentes de modelagem desses transistores consideram dispositivos de canal longo, de forma geral o comprimento utilizado é de 1 µm, de porta dupla ou cilíndricos. Pouco tem sido feito relacionado à modelagem de JNTs porta tripla e a influência da temperatura no funcionamento dos mesmos. Assim, este trabalho tem como objetivo a modelagem do funcionamento dos dispositivos MOS sem junções de porta tripla quanto à tensão de limiar, potencial de superfície, carga de condução e corrente de dreno. Os modelos são derivados da solução da equação de Poisson com as condições de contorno adequadas, apresentando grande concordância com simulações numéricas tridimensionais e com resultados experimentais para dispositivos com comprimento de canal de até 30 nm. No caso do modelo da tensão de limiar, o maior erro obtido entre modelo e simulação foi de 33 mV, que representa uma percentagem menor que 5 %. Também foi apresentado um método de extração da tensão de limiar baseado na igualdade das componentes de deriva e difusão da corrente de dreno. Este método foi igualmente validado com resultados simulados, apresentando um erro máximo de 3 mV (menor que 0,5 %) e aplicado à dispositivos experimentais. A influência da temperatura na tensão de limiar também foi analisada tanto pelo modelo proposto como por simulações e resultados experimentais, mostrando que a dependência da concentração de dopantes ionizados com a temperatura devido à ionização incompleta dos portadores tem grande influência na tensão de limiar. No caso da modelagem da corrente de dreno e do potencial de superfície, foi acrescentada uma correção de efeitos de canal curto. O erro médio foi menor que 12 % para as curvas de corrente e suas derivadas quando comparadas à dos dispositivos experimentais de comprimento de canal de 30 nm. Também foi realizado um estudo do funcionamento dos JNTs, mostrando que o ponto invariante com a temperatura, onde a corrente de dreno se mantém constante independente da temperatura, pode ou não existir nesses dispositivos dependendo da resistência série e de sua dependência com a temperatura. Por fim, a operação analógica dos dispositivos sem junções é analisada para dispositivos de diferentes dimensões. / In this work, a study of the Junctionless Nanowire Transistors (JNTs) is presented, focusing their modeling and analyzing their operation. The JNTs are heavily doped devices with a doping concentration constant from source to drain, without presenting doping gradients. They have been developed in order to avoid drain and source ion implantation, which requires rigorous controlled conditions to avoid dopants diffusion into the channel in extremely reduced devices (sub-20 nm). Therefore, these devices provide a higher scalability with a simplified fabrication process. Recent works on junctionless nanowire transistors modeling have considered long-channel (a length of 1 µm is commonly used) double-gate or cylindrical devices. Few works have presented the modeling of triple-gate JNTs and the temperature influence on the device operation. The goal of this work is the modeling of the threshold voltage, surface potential, conduction charge and drain current in triple-gate junctionless nanowire transistors. The models are derived from the solution of the Poisson equation with the appropriate boundary conditions and exhibit a great concordance with three-dimensional numerical simulations and experimental data even for devices with channel length of 30 nm. In the case of the threshold voltage, the higher error obtained between model and simulation was 33 mV, which represents an error lower than 5 %. A method for the threshold voltage extraction based on the equality of the drift and diffusion components of the drain current has also been presented. This method was also validated using simulated results, with a maximum error of 3 mV (lower than 0.5 %), and applied to experimental devices. The influence of the temperature on the threshold voltage has also been analyzed through the proposed model, the numerical simulations and the experimental data. It has been shown that the dependence of the ionized dopant concentration with the temperature due to the incomplete carrier ionization has a great influence on the threshold voltage. In the case of the surface potential and drain current modeling, a correction for the short channel effects has been proposed. The mean error has been lower than 12 % for the drain current curves and their derivatives when compared to the ones of experimental devices with a channel length of 30 nm. An analysis on the operation of the JNTs has been also performed, showing that the zero temperature coefficient point, in which the current is the same independent of the temperature, can or not exist depending on the series resistance and its dependence on the temperature. Finally, the operation of junctionless nanowire transistors in analog applications has been analyzed for devices of different dimensions.

O substrato de nanofios (MnM) é uma nova tecnologia de interposers visando aplicações em ondas-mm que vêm recebendo atenção devido à facilidade de se fabricar vias de interconexão e estruturas de onda lenta de alto desempenho com resultados no estado-da-arte. Entretanto, embora as estruturas de interconexão, como vias e linhas de transmissão, já estejam bem definidas, ainda não se verificou a viabilidade de se usar essa tecnologia como base para antenas planares, uma parte vital de qualquer aplicação de transmissão de dados sem fio. Esse trabalho visa preencher essa lacuna, apresentando métodos para se realizar a caracterização elétrica do substrato através da extração de sua constante dielétrica relativa e tangente de perdas, e para se projetar antenas de uso frequente em aplicações de ondas-mm através de softwares de simulação eletromagnética. Esse trabalho apresenta também as etapas de fabricação da tecnologia numa visão geral e aplicada às estruturas desenvolvidas, seguida da caracterização das estruturas até 110 GHz. Os resultados mostraram um substrato com constante dielétrica relativa de 7 ± 0,2 e com tangente de perdas de 0,03 ± 0,005. Simulações das antenas projetadas mostraram que o substrato MnM é um candidato viável para antenas do tipo end-fire, cuja irradiação acontece paralela ao plano do substrato, devido ao fato dos parâmetros do substrato não interferirem demasiadamente na eficiência de irradiação desse tipo de antena. Entretanto, as simulações também mostraram que esse substrato é um candidato ruim para antenas tipo back-fire, com irradiação perpendicular ao plano do substrato, devido às baixas figuras de eficiência de irradiação e ganho. / The nanowire substrate (MnM) is a novel interposer technology for mm-waves applications that has been receiving more and more attention thanks to the ease of fabricating high performance interconnection vias and slow-wave structures, whose results are in the state-of-the-art. However, even though the interconnection structures, such as transmission lines and vias, are already well-defined, no one has analyzed the potential of the MnM substrate as a planar antenna substrate, a core component of any wireless communications application. This work aims to fill this gap by presenting substrate characterization methods, that involves determining its dielectric constant and loss tangent, and by presenting planar antenna design methods using electromagnetic simulation softwares. This work presents also a general overview of the manufacturing processes being developed, followed by structure measurement up until 110 GHz. The results showed a substrate with a dielectric constant of 7 ± 0.2 and with a loss tangent of 0.03 ± 0.005. Simulations of the designed antennas indicated that this substrate is a viable choice for end-fire antennas, whose radiation is parallel to the plane of the substrate, because the substrate parameters doesn\'t seem to degrade the radiation efficiency of this kind of antenna. However, simulations also showed that the MnM substrate is a poor candidate for back-fire antennas, whose radiation is perpendicular to the plane of the substrate, given the low figures of radiation efficiency and gain.

O substrato de nanofios (MnM) é uma nova tecnologia de interposers visando aplicações em ondas-mm que vêm recebendo atenção devido à facilidade de se fabricar vias de interconexão e estruturas de onda lenta de alto desempenho com resultados no estado-da-arte. Entretanto, embora as estruturas de interconexão, como vias e linhas de transmissão, já estejam bem definidas, ainda não se verificou a viabilidade de se usar essa tecnologia como base para antenas planares, uma parte vital de qualquer aplicação de transmissão de dados sem fio. Esse trabalho visa preencher essa lacuna, apresentando métodos para se realizar a caracterização elétrica do substrato através da extração de sua constante dielétrica relativa e tangente de perdas, e para se projetar antenas de uso frequente em aplicações de ondas-mm através de softwares de simulação eletromagnética. Esse trabalho apresenta também as etapas de fabricação da tecnologia numa visão geral e aplicada às estruturas desenvolvidas, seguida da caracterização das estruturas até 110 GHz. Os resultados mostraram um substrato com constante dielétrica relativa de 7 ± 0,2 e com tangente de perdas de 0,03 ± 0,005. Simulações das antenas projetadas mostraram que o substrato MnM é um candidato viável para antenas do tipo end-fire, cuja irradiação acontece paralela ao plano do substrato, devido ao fato dos parâmetros do substrato não interferirem demasiadamente na eficiência de irradiação desse tipo de antena. Entretanto, as simulações também mostraram que esse substrato é um candidato ruim para antenas tipo back-fire, com irradiação perpendicular ao plano do substrato, devido às baixas figuras de eficiência de irradiação e ganho. / The nanowire substrate (MnM) is a novel interposer technology for mm-waves applications that has been receiving more and more attention thanks to the ease of fabricating high performance interconnection vias and slow-wave structures, whose results are in the state-of-the-art. However, even though the interconnection structures, such as transmission lines and vias, are already well-defined, no one has analyzed the potential of the MnM substrate as a planar antenna substrate, a core component of any wireless communications application. This work aims to fill this gap by presenting substrate characterization methods, that involves determining its dielectric constant and loss tangent, and by presenting planar antenna design methods using electromagnetic simulation softwares. This work presents also a general overview of the manufacturing processes being developed, followed by structure measurement up until 110 GHz. The results showed a substrate with a dielectric constant of 7 ± 0.2 and with a loss tangent of 0.03 ± 0.005. Simulations of the designed antennas indicated that this substrate is a viable choice for end-fire antennas, whose radiation is parallel to the plane of the substrate, because the substrate parameters doesn\'t seem to degrade the radiation efficiency of this kind of antenna. However, simulations also showed that the MnM substrate is a poor candidate for back-fire antennas, whose radiation is perpendicular to the plane of the substrate, given the low figures of radiation efficiency and gain.

Les microcavités à grand facteur de qualité et faible volume modal permettent, grâce à un fort effet de confinement de la lumière, le renforcement des interactions lumière-Matière et la réalisation de futurs dispositifs pour le traitement optique de l’information à faible énergie de commande. Ce travail de thèse traite du fonctionnement de microcavités à cristal photonique en régime d’excitation cohérente, basé sur des impulsions dont la relation temps-Fréquence est contrôlée afin de renforcer les interactions non linéaires intracavité.La modélisation de la dynamique non linéaire de ces cavités à l'aide de la théorie des modes couplés, a permis de mettre en avant le rôle des non-Linéarités réfractives sur la réduction des effets de localisation au cours de l'excitation.Nous proposons alors de contrôler la dynamique du champ intracavité par un contrôle de la relation temps-Fréquence des impulsions.Cette excitation dite cohérente, repose sur la mise en œuvre d'un montage de mise en forme d'impulsions, constitué d'un étireur d'impulsions et d'un dispositif de filtrage spectral.La caractérisation non linéaire de nanoguides en silicium a permis, en complément du modèle, la détermination précise des paramètres des impulsions.Nous avons ensuite réalisé la toute première démonstration expérimentale de l'excitation cohérente de microcavités, menant à la fois à un renforcement des interactions non linéaires et une réduction des distorsions subies par les impulsions transmises par la cavité. / High quality factor and small modal volume microcavities allow, thanks to a strong light confinement, an enhancement of light matter interactions and the realization of low energy consumption devices for optical signal processing.In this work, we study the coherent excitation of nonlinear photonic crystal resonators, which is achieved by controlling the pulse time-Frequency relation, enabling nonlinear interaction enhancement.A modeling of the intra-Cavity nonlinear dynamics is conducted using the coupled mode theory, underlying the nonlinear refractive effects contribution in the intra-Cavity pulse energy reduction and distortion.We show that an appropriate pulse time-Frequency relation allow to compensate for the cavity resonance frequency shift, and to maintain the benefit of light localization during the entire excitation.The pulse shaper, made of a pulse-Stretcher combined with a spectral filter, has been specifically designed.Preliminary nonlinear characterizations of silicon nanowires enable to determine the shaped pulses parameters.A very first experimental coherent excitation of an optical resonator is reported, leading to a nonlinear interaction enhancement, and to the control of both the optical bandwidth and nonlinear dynamics of the cavity.

Neste trabalho é apresentado um estudo dos transistores MOS sem junções (Junctionless Nanowire Transistors - JNTs), cujo foco é a modelagem de suas características elétricas e a análise do funcionamento dos mesmos quanto à tensão de limiar, ponto invariante com a temperatura e operação analógica. Os JNTs possuem uma concentração de dopantes constante da fonte ao dreno sem apresentar gradientes. Eles foram desenvolvidos a fim de se evitar as implantações iônicas de fonte e dreno, que requerem condições rigorosamente controladas para se evitar a difusão de dopantes para o interior do canal em dispositivos de tamanho extremamente reduzido (sub-20 nm). Dessa forma, esses dispositivos permitem um maior escalamento, com um processo de fabricação simplificado. Os trabalhos recentes de modelagem desses transistores consideram dispositivos de canal longo, de forma geral o comprimento utilizado é de 1 µm, de porta dupla ou cilíndricos. Pouco tem sido feito relacionado à modelagem de JNTs porta tripla e a influência da temperatura no funcionamento dos mesmos. Assim, este trabalho tem como objetivo a modelagem do funcionamento dos dispositivos MOS sem junções de porta tripla quanto à tensão de limiar, potencial de superfície, carga de condução e corrente de dreno. Os modelos são derivados da solução da equação de Poisson com as condições de contorno adequadas, apresentando grande concordância com simulações numéricas tridimensionais e com resultados experimentais para dispositivos com comprimento de canal de até 30 nm. No caso do modelo da tensão de limiar, o maior erro obtido entre modelo e simulação foi de 33 mV, que representa uma percentagem menor que 5 %. Também foi apresentado um método de extração da tensão de limiar baseado na igualdade das componentes de deriva e difusão da corrente de dreno. Este método foi igualmente validado com resultados simulados, apresentando um erro máximo de 3 mV (menor que 0,5 %) e aplicado à dispositivos experimentais. A influência da temperatura na tensão de limiar também foi analisada tanto pelo modelo proposto como por simulações e resultados experimentais, mostrando que a dependência da concentração de dopantes ionizados com a temperatura devido à ionização incompleta dos portadores tem grande influência na tensão de limiar. No caso da modelagem da corrente de dreno e do potencial de superfície, foi acrescentada uma correção de efeitos de canal curto. O erro médio foi menor que 12 % para as curvas de corrente e suas derivadas quando comparadas à dos dispositivos experimentais de comprimento de canal de 30 nm. Também foi realizado um estudo do funcionamento dos JNTs, mostrando que o ponto invariante com a temperatura, onde a corrente de dreno se mantém constante independente da temperatura, pode ou não existir nesses dispositivos dependendo da resistência série e de sua dependência com a temperatura. Por fim, a operação analógica dos dispositivos sem junções é analisada para dispositivos de diferentes dimensões. / In this work, a study of the Junctionless Nanowire Transistors (JNTs) is presented, focusing their modeling and analyzing their operation. The JNTs are heavily doped devices with a doping concentration constant from source to drain, without presenting doping gradients. They have been developed in order to avoid drain and source ion implantation, which requires rigorous controlled conditions to avoid dopants diffusion into the channel in extremely reduced devices (sub-20 nm). Therefore, these devices provide a higher scalability with a simplified fabrication process. Recent works on junctionless nanowire transistors modeling have considered long-channel (a length of 1 µm is commonly used) double-gate or cylindrical devices. Few works have presented the modeling of triple-gate JNTs and the temperature influence on the device operation. The goal of this work is the modeling of the threshold voltage, surface potential, conduction charge and drain current in triple-gate junctionless nanowire transistors. The models are derived from the solution of the Poisson equation with the appropriate boundary conditions and exhibit a great concordance with three-dimensional numerical simulations and experimental data even for devices with channel length of 30 nm. In the case of the threshold voltage, the higher error obtained between model and simulation was 33 mV, which represents an error lower than 5 %. A method for the threshold voltage extraction based on the equality of the drift and diffusion components of the drain current has also been presented. This method was also validated using simulated results, with a maximum error of 3 mV (lower than 0.5 %), and applied to experimental devices. The influence of the temperature on the threshold voltage has also been analyzed through the proposed model, the numerical simulations and the experimental data. It has been shown that the dependence of the ionized dopant concentration with the temperature due to the incomplete carrier ionization has a great influence on the threshold voltage. In the case of the surface potential and drain current modeling, a correction for the short channel effects has been proposed. The mean error has been lower than 12 % for the drain current curves and their derivatives when compared to the ones of experimental devices with a channel length of 30 nm. An analysis on the operation of the JNTs has been also performed, showing that the zero temperature coefficient point, in which the current is the same independent of the temperature, can or not exist depending on the series resistance and its dependence on the temperature. Finally, the operation of junctionless nanowire transistors in analog applications has been analyzed for devices of different dimensions.

Les propriétés électro-thermo-mécaniques remarquables qui peuvent apparaître dans les nanofils de silicium font l'objet d'un nombre croissant de travaux de recherche. Ces travaux de thèse de nature fortement expérimentale, visent à donner une meilleure connaissance de ces propriétés dans le cas de nanofils, en silicium monocristallin, fabriqués par approche descendante. Pour caractériser la piézorésistivité, deux méthodes de chargement mécaniques ont été développées : la flexion 4 points de puce et la traction/compression in situ avec un actionneur MEMS. La méthode 3ω a été choisie pour des mesures de conductivité thermiques. Ces propriétés ont été étudiées en fonction de la température et la contrainte dans une station sous pointes cryogénique.Les résultats montrent que les nanofils fabriqués à partir de substrats SOI amincis peuvent, de manière inattendue, être fortement contraints en compression après fabrication. Les nanofils de type p présentent, même en régime de mesure dynamique, des coefficients piézorésistifs élevés qui décroissent fortement avec la température et permettent une détection intégrée de mouvement de MEMS avec une limite de détection inférieure à l'Angström. Les mesures thermiques confirment l’effet d’échelle attendu de la conductivité thermique, la décroissance avec la température est compatible avec les résultats théoriques et expérimentaux précédemment publiés. / Remarkable nanoscale electro-thermo-mechanical properties of silicon nanowires are increasingly studies. This experimental thesis investigates such properties for top-down fabricated monocrystal silicon nanowires.A four points bending set-up and a MEMS actuator are developed to apply ex situ and in situ mechanical stress on nanowires. Those devices are characterised in a cryogenic environment within a microprobe station. Electrical properties and piezoresistivity are studied using those systems. Moreover, the 3ω method measures the thermal conductivity of these nanowires.From buckling of silicon nanowires, unexpected high compressive stress (>100 MPa) was identified in top silicon layers of SOI substrates. Drift-compensated measurements show that p type silicon nanowires present large piezoresistive coefficients which decrease with temperature. Additionally, the MEMS device demonstrates the possibility to detect ample MEMS movements with sub-ångström resolution using the nanowires as piezoresistive nanogauges. The thermal conductivity was found consistent with previously reported values for silicon nanowires, and expectedly decreases with temperature.

<div>Germanium-based MOS device which is considered as one of the promising alternative channel materials has been studied with well-known FinFET, nanowire structures and HKMG (High-k metal gate). Recent introduction of Ferroelectric (FE) Zr-doped HfO₂ (Hf_xZr_1-xO₂, HZO) has opened various possibilities both in memory and logic</div><div>applications.</div><div><br></div><div>First, integration of FE HZO into the conventional Ge platform was studied to demonstrate Ge FeFET. The FE oxide was deposited with optimized atomic layer deposition (ALD) recipe by intermixing HfO₂ and ZrO₂. The HZO film was characterized with FE tester, XRD and AR-XPS. Then, it was integrated into conventional gate stack of Ge devices to demonstrate Ge FeFETs. Polarization switching was measured with ultrafast measurement set-up down to 100 ps.</div><div><br></div><div>Then, HZO layer was controlled for the first demonstration of hysteresis-free Ge negative capacitance (NC) CMOS FinFETs with sub-60mV/dec SS bi-directionally at room temperature towards possible logic applications. Short channel effect in Ge NCFETs were compared with our reported work to show superior robustness. For smaller widths that cannot be directly written by the e-beam lithography tool, digital etching on Ge fins were optimized.</div><div>Lastly, Ge FeFET-based synaptic device for neuromorphic computing was demonstrated. Optimum pulsing schemes were tested for both potentiation and depression which resulted in highly linear and symmetric conductance profiles. Simulation was done to analyze Ge FeFET's role as a synaptic device for deep neural network.</div>