Ce travail de thèse traite les domaines du rayonnement d'antennes basses fréquences et de la propagation du champ électromagnétique, en présence du sol et d'environnement réalistes. Des éléments qui diffèrent du cas canonique du sol plan homogène et infini sont considérés par le mot "réalistes". Les méthodes numériques classiques pour l'électromagnétisme, en particulier pour la modélisation du rayonnement d'antennes, sont plutôt adaptées à des fréquences au-delà des hautes fréquences et au rayonnement en espace libre. Deux axes de recherche ont été définis comme suit: les effets d'environnements situés en zone proche sur le rayonnement d'antennes filaires basses fréquences et l'étude de systèmes éloignés de la source par la création d'une méthode hybride. En ce qui concerne le rayonnement en zone proche, une méthode des différences finies dans le domaine temporel est utilisée. Celle-ci est lourde d'un point de vue des temps de calculs et de l'occupation de la mémoire, cependant elle est effective du fait du maillage volumique de la scène. Dans le cas de la propagation lointaine, la solution parfaite du rayonnement d'un dipôle infinitésimal électrique vertical au-dessus d'un sol plan homogène infini a été traitée par la création d'un algorithme adaptatif d'intégration numérique. Ce dernier permet d'obtenir les valeurs du champ électromagnétique dans tout l'espace avec une précision numérique contrôlée. Une technique originale d'hybridation a été réalisée entre l'algorithme d'intégration et la méthode des différences finies pour rendre compte efficacement des effets d'éléments lointains sur la propagation du champ. / This work is about the radiation of low frequency antennas and the propagation of the electromagnetic field, in the presence of soil and realistic environments. Elements that differ from the canonical case of homogeneous infinite and planar ground are considered by the word realistic. Conventional numerical methods for electromagnetism, in particular for modeling the radiation of antennas are rather suitable for frequencies beyond the high frequencies and in free space. Two research areas were defined as follows : the effects of environments located near the low frequency wire antennas and the study of systems far from the source through the creation of a hybrid method. Regarding the near-field radiation, a method of finite-difference in the time-domain is used. It needs a large computer memory size and long solution times, however it is effective because the entire scene is included in a volumetric mesh. In the case of field propagation, the radiation of a vertical electric current element above a homogeneous flat ground has been computed with the creation of an adaptive algorithm for numerical inte- gration. This allows to obtain the values of the electromagnetic field in the whole space with controlled numerical accuracy. An original technique of hybridization was performed between the integration algorithm and the method of finite differences to effectively observ the effects of distant elements on the field propagation.

A redução das dimensões dos dispositivos semicondutores para escalas submicrométricas impõe diversos desafios no projeto de circuitos integrados. O impacto das variações intrínsecas afetando parâmetros elétricos cresce em importância à medida que a área dos dispositivos adentra a faixa nanométrica. Dentre essas variações estão flutuações nas tensões e correntes de terminal causadas pelas diferentes formas de ruído intrínseco dos dispositivos MOS. Este trabalho apresenta um estudo sobre o impacto do ruído elétrico no desempenho de circuitos MOS. Um novo modelo para simulação do Random Telegraph Signal (RTS) no domínio do tempo é utilizado. Uma metodologia de simulação para contabilizar o ruído térmico em simulações transientes também é proposta. A partir desses modelos de simulação de dispositivos, o trabalho de pesquisa analisa o impacto da variabilidade de parâmetros elétricos em nível de circuito. As simulações focam na caracterização da pureza espectral em osciladores em anel de sinal diferencial. Diversas topologias são apresentadas e posteriormente comparadas em termos do jitter no período de oscilação. / The shrinking of semiconductors devices dimensions to submicron scales introduces many challenges in integrated circuit design. The impact of intrinsic variability affecting electrical parameters increases in importance as transistors enter the nanometric range. Among these variations are fluctuations in terminal voltages and currents caused by different forms of intrinsic noise of MOS devices A new model for Random Telegraph Signal (RTS) simulation in time-domain is utilized. A simulation methodology to account for thermal noise effects in transient simulations is also proposed. Using these simulation models, this research work analyses the impact of electrical noise at circuit level. The simulations focus on the characterization of spectral purity in differential ring oscillators. Different topologies are presented and compared in terms of jitter in the period of oscillation.

Les transistors organiques attirent actuellement beaucoup d'attention en raison des avantages uniques par rapport à leur homologue inorganique. En revanche, la compréhension physique du fonctionnement et du transport des porteurs de charge est très limitée. L'objectif de cette thèse est de contribuer à apporter une meilleure compréhension des transistors organiques. Le Chapitre 1 présente les semi-conducteurs organiques : le mécanisme de conduction, les paramètres essentiels, les matériaux typiques etc. Le Chapitre 2 discute des transistors organi-ques en termes de structures, de mécanismes de fonctionnement, de paramètres principaux et des procédés de fabrication. Le Chapitre 3 étudie la caractérisation statique. Après les méthodes classiques, la méthode de la fonc-tion Y est introduite. Subséquemment, des techniques pour extraire les paramètres principaux sont présentées sé-parément. Enfin, les résultats expérimentaux sur nos échantillons sont exposés. Sur la base des données mesurées, les travaux de modélisation sont présentés dans le chapitre 4. Premièrement, une solution de l'équation Poisson est introduite qui donne la distribution de potentiel et donc la distribution de porteurs dans le film organique. Avec la prise en compte des pièges, les résultats obtenus par simulation sont en bon accord avec les données expérimen-tales. A partir de mesures des caractéristiques de courant –tension effectuées à basse température, on propose une procédure d'analyse de la mobilité en utilisant l'intégrale de Kubo-Greenwood. Ensuite, prenant en compte la dis-tribution de porteurs dans le film organique, une solution de l'équation de Poisson est donnée et la mobilité effec-tive est calculée en fonction de la tension de grille et de la température. Le Chapitre 5 est consacré à l'analyse du bruit à basse fréquence. On étudie d'abord le bruit du canal où une domination du bruit provenant des contacts est observée. En conséquence, une méthode TLM pour l'extraction du bruit des contacts est présentée. Ensuite, un procédure d'analyse des sources de bruit dû au contact est aussi proposée. Les résultats de bruit obtenus sur des transistors organiques de différentes origines sont également discutés à la fin. / Organic transistors recently attract much attention because of their unique advantages over the conventional inorganic counterparts. However, the understanding of their operating mechanism and the carrier transport process are still very limited, this thesis is devoted to such a subject. Chapter 1 presents the organic semiconductors regarding carrier transport, parameters, typically applied materials. Chapter 2 describes the issues related to organic transistors: structure, operating mechanism, principal parameters and fabrication technologies. Chapter 3 deals with the static properties characterization. The commonly used methods are firstly presented and then the Y function method is introduced. Afterwards, the characterization methods for principles parameters are separately discussed. The experimental results on our organic transistors are finally described. Chapter 4 focuses on the mod-eling on the basis of the experimental data, regarding DC characteristics modeling with a solution for Poisson's equation, carrier mobility modeling with using Kubo-Greenwood integral as well as a theoretical analysis of OFETs' carrier mobility involving a solution of Poisson's equation. Chapter 5 analyzes the low-frequency noise in organic transistors. One firstly addresses the channel noise sources and then concentrates on the contact noise extraction and contact noise sources diagnosis. The noise measurements on other samples are also presented.

A redução das dimensões dos dispositivos semicondutores para escalas submicrométricas impõe diversos desafios no projeto de circuitos integrados. O impacto das variações intrínsecas afetando parâmetros elétricos cresce em importância à medida que a área dos dispositivos adentra a faixa nanométrica. Dentre essas variações estão flutuações nas tensões e correntes de terminal causadas pelas diferentes formas de ruído intrínseco dos dispositivos MOS. Este trabalho apresenta um estudo sobre o impacto do ruído elétrico no desempenho de circuitos MOS. Um novo modelo para simulação do Random Telegraph Signal (RTS) no domínio do tempo é utilizado. Uma metodologia de simulação para contabilizar o ruído térmico em simulações transientes também é proposta. A partir desses modelos de simulação de dispositivos, o trabalho de pesquisa analisa o impacto da variabilidade de parâmetros elétricos em nível de circuito. As simulações focam na caracterização da pureza espectral em osciladores em anel de sinal diferencial. Diversas topologias são apresentadas e posteriormente comparadas em termos do jitter no período de oscilação. / The shrinking of semiconductors devices dimensions to submicron scales introduces many challenges in integrated circuit design. The impact of intrinsic variability affecting electrical parameters increases in importance as transistors enter the nanometric range. Among these variations are fluctuations in terminal voltages and currents caused by different forms of intrinsic noise of MOS devices A new model for Random Telegraph Signal (RTS) simulation in time-domain is utilized. A simulation methodology to account for thermal noise effects in transient simulations is also proposed. Using these simulation models, this research work analyses the impact of electrical noise at circuit level. The simulations focus on the characterization of spectral purity in differential ring oscillators. Different topologies are presented and compared in terms of jitter in the period of oscillation.

A redução das dimensões dos dispositivos semicondutores para escalas submicrométricas impõe diversos desafios no projeto de circuitos integrados. O impacto das variações intrínsecas afetando parâmetros elétricos cresce em importância à medida que a área dos dispositivos adentra a faixa nanométrica. Dentre essas variações estão flutuações nas tensões e correntes de terminal causadas pelas diferentes formas de ruído intrínseco dos dispositivos MOS. Este trabalho apresenta um estudo sobre o impacto do ruído elétrico no desempenho de circuitos MOS. Um novo modelo para simulação do Random Telegraph Signal (RTS) no domínio do tempo é utilizado. Uma metodologia de simulação para contabilizar o ruído térmico em simulações transientes também é proposta. A partir desses modelos de simulação de dispositivos, o trabalho de pesquisa analisa o impacto da variabilidade de parâmetros elétricos em nível de circuito. As simulações focam na caracterização da pureza espectral em osciladores em anel de sinal diferencial. Diversas topologias são apresentadas e posteriormente comparadas em termos do jitter no período de oscilação. / The shrinking of semiconductors devices dimensions to submicron scales introduces many challenges in integrated circuit design. The impact of intrinsic variability affecting electrical parameters increases in importance as transistors enter the nanometric range. Among these variations are fluctuations in terminal voltages and currents caused by different forms of intrinsic noise of MOS devices A new model for Random Telegraph Signal (RTS) simulation in time-domain is utilized. A simulation methodology to account for thermal noise effects in transient simulations is also proposed. Using these simulation models, this research work analyses the impact of electrical noise at circuit level. The simulations focus on the characterization of spectral purity in differential ring oscillators. Different topologies are presented and compared in terms of jitter in the period of oscillation.

O sistema atmosfera-gelo marinho é complexo e fortemente acoplado. Em uma região de transição entre a cobertura de gelo marinho e o mar aberto a interação entre esse sistema é particularmente intensa, sendo significativa o suficiente para influenciar a circulação atmosférica de grande escala e a distribuição de gelo marinho. Assim, o objetivo principal deste trabalho foi analisar as interações entre os ciclones extratropicais e a variabilidade extrema do gelo marinho nos setores dos mares de Bellingshausen-Amundsen (MBA) e do mar de Weddell (MW), no período de verão e inverno austral entre 1989 e 2007. Foram utilizados dados de extensão de gelo marinho do NSIDC/NASA; campos atmosféricos da superfície até os altos níveis da troposfera das reanálises do ERA-Interim (ECMWF); composição de imagens de satélite do canal infravermelho do SSEC; Índice de Niño Oceânico do CPC/NOAA. As anomalias de alta frequência (período de 2-10 dias) e interanual (período maior que 370 dias) foram obtidas aplicando-se a transformada rápida de Fourier nas séries temporais (1989-2007). Os extremos de gelo marinho foram obtidos através do primeiro e terceiro quartil da distribuição dos dados. As características da circulação atmosférica de alta frequência e interanual associadas aos eventos extremos negativos (ENGM) e positivos (EPGM) de gelo marinho, na mesma escala de tempo, foram obtidas através de composições defasadas das anomalias dos campos atmosféricos. Para evidenciar e exemplificar os padrões encontrados nas composições de alta frequência apresenta-se uma análise sinótica de estudo de casos para o setor dos MBA durante o inverno austral, em eventos ENGM e EPGM, separando os casos em fases distintas do fenômeno tropical El Niño. Foi utilizada a estatística de ciclones do Automatic Cyclone Tracking, da Universidade de Melbourne, para analisar a ocorrência de ciclones associados aos períodos de mínima e máxima extensão de gelo marinho na escala interanual. Os resultados mostram que no verão e inverno austral, os eventos ENGM de alta frequência no setor dos MBA e do MW estão associados com as anomalias dos campos atmosféricos, na mesma escala temporal, que se assemelham a um trem de ondas ocorrido a partir de três dias anteriores ao evento extremo. A anomalia ciclônica no oeste e a anomalia anticiclônica no leste do setor resultam em uma anomalia de ventos de norte e, consequentemente, a anomalias positivas de temperatura do ar. Essa configuração anômala contribui para os eventos ENGM através do derretimento do gelo marinho e do seu próprio transporte em direção às latitudes maiores pelos ventos de norte anômalos. As anomalias de alta frequência dos campos atmosféricos em todos os casos (composições defasadas) de eventos EPGM apresentam fases opostas em relação aos eventos ENGM. Portanto, fases distintas do trem de ondas induzem na modulação de extremos de gelo marinho opostos. Em relação às análises sinóticas dos eventos ENGM e EPGM em fases distintas do fenômeno El Niño, verificou-se que em períodos de El Niño há uma intensificação do jato subtropical e um enfraquecimento do jato polar no Pacífico Sul. Há uma menor atuação dos ciclones extratropicais, predominando o sistema de cristas e cavados. Na fase de La Niña há um reforço do jato polar e uma intensa atividade ciclônica sobre os MBA. No evento ENGM (EPGM) há uma associação entre os ventos de norte (de sul) com a vanguarda (retaguarda) dos sistemas ciclônicos em superfície. Na fase Neutra verificou-se uma intensificação do jato polar e uma atuação do sistema de cristas/cavados e de sistemas ciclônicos em superfície. Na análise da influência da circulação atmosférica interanual na variabilidade extrema do gelo marinho, na mesma escala de tempo, observou-se que a fase quente (fria) do ENSO provavelmente está associada com eventos ENGM (EPGM) nos MBA e com eventos EPGM (ENGM) no MW. Sobre a influência da variabilidade interanual da extensão do gelo marinho na atividade ciclônica, nas composições de anomalias interanuais de PNMM em relação aos eventos ENGM nos MBA (lag = 0) no verão, há um predomínio de anomalias positivas de pressão ao nível médio do mar (PNMM) sobre grande parte do Oceano Austral, o que contribuiria para uma menor profundidade e raio dos sistemas em superfície. Já em relação aos eventos ENGM no MW, verifica-se que no lag = 0 há um predomínio de anomalias negativas de PNMM no Oceano Austral, o que contribuiria para um aumento da profundidade e raio dos ciclones. / The sea ice-atmosphere system is complex and tightly coupled. In a transition region between the coverage of sea ice and open ocean the interaction between this system is particularly intense, being significant enough to influence large-scale atmospheric circulation and sea ice distribution. Thus, the main objective of this study was to analyze the interactions between extratropical cyclones and extreme variability of sea ice in the sectors of the Bellingshausen-Amundsen Seas (BAS) and the Weddell Sea (WS), in the period of austral summer and winter between 1989 and 2007. We used sea ice extent data from NSIDC/NASA; atmospheric fields (surface to higher tropospheric levels) from ERA-Interim reanalysis; SSEC IR satellite image composition; and the Oceanic Niño Index CPC/NOAA. Anomalies of high-frequency (2-10 days) and interannual (longer than 370 days) were obtained by applying a fast Fourier transform in the time series (1989-2007). The extremes of sea ice were obtained from the first and third quartile of the data distribution. The characteristics of high-frequency atmospheric circulation and interannual associated with negative (NESI) and positive (PESI) extreme events of sea ice at the same time scale, were obtained from the lagged composites of the anomalies of atmospheric fields. To highlight and illustrate the patterns found in the composites of high frequency presents a synoptic analysis of case studies for the sector of the BAS during the austral winter at NESI and PESI events, separating the cases in different stages of the tropical El Niño phenomenon. Was used a statistical cyclone of Automatic Cyclone Tracking, from University of Melbourne, to analyze the occurrence of cyclones associated with periods of minimum and maximum extent of sea ice in the interannual scale. The results show that in the austral summer and winter, the NESI events of high frequency in the sector of the BAS and the WS are associated with the anomalies of atmospheric fields in the same timescale that resemble a wave train occurring from three days before the extreme event. The cyclonic anomaly in the west and anticyclonic anomaly in the east sector result in an anomaly of north winds and, consequently, the positive anomalies of air temperature. This anomalous configuration contributes for events NESI by sea ice melting and its own transport to higher latitudes by anomalous north winds. Synoptic atmospheric fields anomalies, in all PESI event cases are in opposite phases to NESI events. Therefore, different phases of the circumpolar wave train induce modulation of concurrent sea ice extremes. Regarding the synoptic analysis of events NESI and PESI in different phases of El Niño, it was found that during periods of El Niño it has a strengthening of the subtropical jet and a weakening of the polar jet in the South Pacific. There is less activity of extratropical cyclones, and the predominant system of ridge and troughs. In the La Niña case studies, has a strengthening of the polar jet and an intense cyclonic activity over the BAS. In the NESI (PESI) event there is an association between the north (south) winds at the vanguard (rear) of the cyclone systems at surface. In the Neutral phase case studies, there is an intensification of the polar jet and performance of the system of ridge/troughs and cyclonic systems at surface. In the analysis of the influence of interannual atmospheric circulation on extreme variability of sea ice, at the same time scale, it was observed that the warm (cold) phase of ENSO are probably associated with NESI (PESI) events at BAS and with PESI (NESI) events in the WS. On the influence of interannual variability of sea ice extent in the cyclonic activity, in the composites of interannual anomalies of mean sea level pressure (MSLP) in relation to NESI events in the BAS (lag = 0) in the summer, there is a predominance of positive anomalies of MSLP over much of the Southern Ocean, which would contribute to a lower depth and radius of the surface systems. In relation to NESI events in WS, it appears that in the lag = 0 there is a predominance of negative anomalies of MSLP in the Southern Ocean, which would contribute to an increase in depth and radius cyclones.

Abstract Osteoporotic hip fractures are associated with high mortality and morbidity rates as well as significant costs. Low-frequency (LF) axial transmission ultrasound is a promising modality for assessing mineral density and geometrical properties. Thus, it may yield additional information on the risk of osteoporotic fractures. This study aimed to evaluate the ability of LF ultrasound to assess osteoporotic status and the risk of fracture in postmenopausal women. Also, lifestyle-related risk factors of hip fractures and the additional discrimination value of combining lifestyle-related risk factors and LF ultrasound velocity were assessed. Two study populations were used. The first consisted of 1,222 older women. Lifestyle-related risk factors and mobility were assessed at baseline. The women were followed for 13 years and the fractures that occurred were recorded. A subgroup of the women was later measured with LF ultrasound and dual-energy x-ray absorptiometry (DXA). The other study population included 95 postmenopausal women whose fracture history was gathered and bone status assessed with LF ultrasound, DXA and peripheral quantitative computed tomography (pQCT). Low body mass and impaired mobility predicted hip fractures. In addition, the risk of cervical hip fracture was increased by low physical activity and decreased by moderate coffee consumption and hypertension. Smoking and old age increased the risk of trochanteric hip fracture. The LF ultrasound velocity reflected to some degree the geometry and bone mineral density of the proximal femur. Decreased low-frequency ultrasound velocity was a significant risk factor of hip fracture even when combined with lifestyle-related risk factors. The LF ultrasound method showed similar fracture discrimination ability compared to DXA and pQCT, especially on the radius. In conclusion, the LF ultrasound method showed promising results in bone characterization and fracture discrimination. Further prospective studies with larger population are needed to confirm the combined effect of clinical risk factors and LF ultrasound. / Tiivistelmä Osteoporoottisiin lonkkamurtumiin liittyy korkean sairastavuuden ja kuolleisuuden lisäksi huomattavat taloudelliset kustannukset. Tässä työssä tutkittiin matalataajuisen ultraäänitekniikan soveltuvuutta osteoporoosin ja murtumariskin arviointiin. Matalataajuista luun pituusakselin suuntaista ultraäänitekniikkaa voidaan käyttää luun mineraalitiheyden ja rakenteen tutkimiseen. Lisäksi tutkittiin elintapoihin liittyviä lonkkamurtuman riskitekijöitä sekä näiden yhdistämistä ultraäänimittaustulosten kanssa riskimalliin. Tutkimuksessa käytettiin kahta tutkimuspopulaatiota. Ensimmäisen muodosti 1222 ikääntynyttä naista, joiden elintavat ja liikuntakyky kartoitettiin tutkimuksen alussa. Kolmentoista vuoden seuranta-ajan aikana tapahtuneet murtumat kerättiin potilasarkistoista. Osa naisista osallistui matalataajuisella aksiaalisuuntaisella ultraäänellä tehtyyn mittaukseen ja kaksienergiseen röntgentutkimukseen (DXA). Toinen tutkimuspopulaatio koostui 95 postmenopausaalisesta naisesta. Naisten murtumahistoria kerättiin ja heille tehtiin matalataajuinen ultraäänimittaus sekä DXA- ja perifeerinen tietokonetomografiatutkimus (pQCT). Alhainen painoindeksi ja heikentynyt liikuntakyky lisäsivät lonkkamurtuman riskiä. Vähäinen fyysinen aktiivisuus lisäsi ja kohtalainen kahvinjuonti ja verenpainetauti alensivat reisiluun kaulan murtumariskiä. Tupakointi ja korkea ikä kasvattivat sarvennoisen alueen lonkkamurtuman riskiä. Matalataajuisen ultraäänen nopeus oli yhteydessä reisiluun yläosan geometriaan ja mineraalitiheyteen. Alhainen ultraäänen nopeus oli merkittävä lonkkamurtuman riskitekijä sekä yksin että yhdistettynä elintapamuuttujiin. Lisäksi ultraäänimenetelmä saavutti röntgenmenetelmiin (DXA ja pQCT) verrattavan erottelukyvyn murtumapotilaiden ja kontrollihenkilöiden välillä. Tutkittu ultraäänimenetelmä osoittautui lupaavaksi työkaluksi luun karakterisoinnissa ja murtumariskin arvioinnissa. Laajempia seurantatutkimuksia tulosten vahvistamiseksi tarvitaan erityisesti elintapoihin liittyvien riskitekijöiden ja ultraäänen yhdistämisen osalta.

Low intensity and low frequency ultrasound has been shown to modulate ion channel currents, membrane capacitive currents, and as a result, neuronal activity. Ultrasound has been used as a non-invasive way to modulate neuronal activity in vivo using mice as well as human subjects. Ultrasound with acoustic frequency as low as 0.35 MHz can be focussed on a region as small as 2 mm with reversible effects and no increase in temperature. In this study, two ultrasound transducers with different resonant frequency have been used to excite neuronal cultures. The resulting changes in the network properties such as synchronised network burst frequency, density, clustering and path length have been analysed. The study shows that ultrasound stimulation at acoustic frequency 450 kHz (ISPPA =11.3 mW/cm2) significantly modulates the above mentioned parameters and causes deviations from small world network properties of the control network.

Avec la diminution constante des dimensions des dispositifs électroniques, les structures MOS font face à de nombreux effets physiques liés à la miniaturisation. Dans le but de maintenir le rythme d'intégration indiqué par la loi de Moore, des nouvelles technologies, dont la structure résiste plus à ces effets physiques, remplacerons le transistor MOSFET bulk. Les modèles physiques permettant de prédire le comportement des transistors MOS atteignent rapidement leurs limites quand ils sont appliqués à ces structures émergentes. Ce travail de thèse est consacré au développement des modèles numériques et analytiques dédiés à la caractérisation des nouvelles architectures SOI et à substrat massif. Nous nous focalisons sur la modélisation du courant de drain basée sur le potentiel de surface, ainsi qu'à la modélisation du comportement en bruit basse fréquence de ces nouveaux dispositifs. Nous proposons un modèle explicite décrivant les potentiels de surface avant et arrière d'une structure SOI. Nous développons ensuite un modèle de bruit numérique et analytique permettant de caractériser les différents oxydes d'une structure FD SOI. La dernière partie de ce mémoire est consacrée à l'étude d'une nouvelle architecture du transistor MOS sur substrat massif. Une caractérisation de la conduction électrique de ce dispositif et de son comportement en bruit basse fréquence sont présentés / With the continuous reduction of the size of MOS devices, various associated short channel effects become significant and limit this scaling. To restrain this limit, multi-gate MOSFET devices seem to be more interesting, thanks to their better control of the gate on the channel. These new devices seem to be good candidates to replace the classical MOS architecture. The existing physical models used to predict the behaviour of MOSFET bulk devices are limited when they are applied to these emerging structures. This thesis is devoted to the development of numerical and analytical models dedicated to the characterization of new SOI architectures and bulk devices. We focus on the modeling of the drain current based on the surface potential as well was the modeling of the low frequency noise behaviour of these devices. We propose an explicit model describing the front and back surface potential of a FD SOI structure. We then develop numerical and analytical low frequency noise models allowing the characterization of the different oxides of a FD SOI structure. The last part of this thesis is devoted to the study of a new architecture of bulk MOS transistors. A characterization of the electrical conduction of this device and its low frequency noise behavior are presented

Gallium Nitride (GaN) high electron mobility transistors (HEMT) have superior performance characteristics compared to Silicon (Si) and Gallium Arsenide (GaAs) based transistors. GaN is a wide bandgap semiconductor which allows it to operate at higher breakdown voltages and power. Unlike traditional semiconductor devices, the GaN HEMT channel region is undoped and relies on the piezoelectric effect created at the GaN and Aluminum Gallium Nitride (AlGaN) heterojunction to create a conduction channel in the form of a quantum well known as the two dimensional electron gas (2DEG). Because the GaN HEMTs are undoped, these devices have higher electron mobility crucial for high frequency operation. However, over time and use these devices degrade in a manner that is not well understood. This research utilizes low frequency noise (LFN) as a method for analyzing changes and degradation mechanisms in GaN-on-Si devices due to gate stress. LFN is a useful tool for probing different regions of the device that cannot be measured through direct means. LFN generation in GaN HEMTs is based on the carrier fluctuation theory of 1/f noise generation which states fluctuations in the number of charge carriers results in conductance fluctuations that produce a Lorentzian noise spectrum. The summing Lorentzian noise spectra from multiple traps leads to 1/f and random telegraph signal (RTS) noise. The primary cause of carrier fluctuations are electron traps near the 2DEG and in the AlGaN bulk. These traps occur naturally due to dislocations and impurities in the manufacturing process, but new traps can be generated by the inverse-piezoelectric effect during gate stress. This thesis introduces noise and presents a circuit to bias the devices and measure gate and drain LFN simultaneously. Three measurements are performed before and after gate DC stress at three different temperatures: DC characterization, capacitance-voltage (C-V) measurements, and LFN measurements. The DC characteristics show an increase in gate leakage after stress caused by an increase in traps after degradation consistent with trap assisted tunneling. However, the leakage current on the drain and source side differ before and after stress leading to the conclusion that the source side of the gate is more sensitive to gate stress. Gate leakage current on the drain side is also sensitive to temperature due to thermionic trap assisted tunneling. Hooge parameter calculations agree with previous research. The LFN results show an increase in gate and drain noise power, SIg(f) and SId(f), in accordance with increased gate leakage current under cutoff bias. RTS noise is also observed to increase in frequency with increased temperature. Activation energies for RTS noise are extracted and qualitatively linked to trap depth based on the McWhorter trap model.