Dans ce travail nous avons élaboré des matériaux ferroélectriques Ba0,9Sr0,1TiO3 (BST) de tailles de plus en plus réduites : céramiques, couches minces et nanoparticules pour des applications en microélectronique. Des matériaux composites constitués de nanoparticules de BST dispersées dans un cristal liquide ont également été réalisés. Le caractère ferroélectrique des films BST a été mis en évidence par des mesures des cycles d'hystérésis électriques. Les meilleures propriétés électriques ont été obtenues avec un recuit à 950 °C pendant 15 mn. Les analyses physico-chimiques sur les nanopoudres BST indiquent que la température optimale de calcination est de 900 °C. La taille des grains obtenue, entre 30 et 100 nm. Les caractérisations par diffraction de rayons X des nanopoudres montrent une structure quadratique à l'ambiante donc la possibilité d'un caractère ferroélectrique de celles-ci. La synthèse de céramiques BST par voie sol-gel et frittées à différentes températures a montré que la taille des grains dépend directement de la température de frittage et s'avère être un paramètre clé influençant la réponse diélectrique du matériau. Les céramiques BST élaborées par la méthode solide-solide permettent d'obtenir une taille de grains supérieure et en conséquence des valeurs de permittivité diélectrique plus élevées. L'étude comparative des propriétés diélectriques du cristal liquide seul et du mélange nanoparticules BST-cristal liquide a confirmé l'influence des nanoparticules BST sur l'orientation des molécules du cristal liquide. La confrontation des résultats expérimentaux aux lois de mélanges a permis l'estimation de la permittivité diélectrique des nanoparticules de BST. / In this work a ferroelectrics Ba0,9Sr0,1TiO3 (BST) ceramics, thin layers and nanoparticles were elaborated in order to obtain suitable materials for microelectronics. A mixture of BST nanoparticles dispersed in a liquid crystal was also performed. The ferrolectric nature of BST films has been demonstrated by measurements of the electrical hysteresis cycles. The best electrical properties were obtained with annealing at 950 °C for 15 min. The physico-chemical analyzes of BST nanapowders indicate that the optimum calcination temperature is at 900 °C. The grain size obtained is between 30 and 100 nm. The characterizations of nanapowders with X-Ray Diffraction show a tetragonal structure at room temperature therefore the possibility of a ferroelectric character. The ceramics synthesized by sol-gel method and sintered at different temperatures showed that the grain size depends directly on the sintering temperature and proves to be a key parameter influencing the dielectric response of the material. The BST ceramics prepared by solid-solid method used to get a size larger grain and consequently a higher value of dielectric permittivity. The comparative study of the dielectric properties of the liquid crystal single and the mixture "BST nanoparticles- liquid crystal" confirmed the influence of nanoparticles on the orientation of liquid crystal molecules. The comparison of experimental results with the mixtures laws allowed the estimation of the dielcectric permittivity of BST nanoparticles.

Este trabalho descreve um estudo sistemático da influência da adição do átomo de lantânio na estrutura da fase Bi4Ti3O12 (BIT) e do átomo érbio na fase Bi3,25La0,75Ti3O12 (BLT075) no que tange seu processo de síntese e suas propriedades estruturais, microestruturais e elétricas. Cerâmicas de composição nominal Bi4-xLaxTi3O12 (BLTx) com 0 x 2 mol % e Bi3,25La0,75Ti3O12 (BLT075) com substituição no sítio do La3+ (BLExT) e no sítio do Ti4+ (BLTEx) com 0 x 0,06 mol %, foram preparadas através do método de síntese por reação do estado sólido. Os dados de difração de raios X (DRX) das amostras BLTx mostram a formação de uma solução sólida para todas as amostras, exceto para amostra contendo 2 mol% de La3+. Verificou-se que a adição de La3+ leva a um aumento da temperatura de sinterização e diminui o tamanho médio dos grãos, alterando sua morfologia de grão na forma de placas para uma forma mais esférica. Quanto às propriedades dielétricas, amostras BLTx com x 1 mol% apresentam um comportamento característico de um ferroelétrico normal, enquanto que quando x > 1 mol%, observa-se um pequeno deslocamento da temperatura de máximo da permissividade dielétrica (Tm) com a freqüência, indicando a existência de um comportamento típico de materiais ferroelétricos relaxores. Os resultados de espectroscopia Raman sugerem que os íons La3+ tendem a ocupar preferencialmente o sítio do Bi3+ das camadas peroviskitas quando x < 1,0 mol %, enquanto que quando x >1,0 mol %, o processo de incorporação também ocorre no sítio do Bi3+ nas camadas de Bi2O2. De acordo com a analise dos espectros XANES e XPS, a estrutura local e eletrônica dos átomos de Ti, Bi e La, não são afetadas de forma significativa pela adição de lantânio.Em relação às amostras dos sistemas BLExT e BLTEx, os dados de DRX mostram somente a presença de fases secundárias nas composições x= 0,04 e 0,06 mol% do sistema no BLTEx. A sinterização à 1115oC possibilitou obter amostras apresentando uma densidade relativa superior a da amostra não dopada BLT075. A adição de Er3+ causa mudanças na morfologia, diminuindo o tamanho médio dos grãos no sistema BLExT e aumentando no sistema BLTEx. Através de medidas elétricas, foi observado um decréscimo no valor Tm em ambos os casos. Quando x > 0,02 mol%, o comportamento de Tm é dominado pelo limite de solubilidade para o sistema BLExT. De acordo com os dados de XAS, a estrutura local e eletrônica dos átomos de Ti e Er não são afetadas de forma significativa pela adição de érbio. / This work describes a systematic study of the influence of the lanthanum atom addition in the Bi4Ti3O12 (BIT) phase and the erbium atom addition in the Bi3,25La0,75Ti3O12 (BLT075) phase in terms of their synthesis process and its structural, microstructural and electrical properties. Ceramics of nominal composition Bi4-xLaxTi3O12 (BLTx) with 0 x 2 mol% and Bi3,25La0, 75Ti3O12 (BLT075) with Er3+ replacing the La3+ atoms (BLExT) and replacing Ti4+ atoms (BLTEx) with 0 x 0, 06 mol%, were prepared by the solid state reaction method. X-ray diffraction (XRD) data of BLTx samples shows the formation of a solid solution for all samples, except for sample containing 2 mol% of La3+. It was found that the addition of La3+ leads to an increase in the sintering temperature, a decrease in the average size of grains and a modification on the grain from plates to a more spherical morphology. The dielectric properties of BLTx samples with x 1 mol% show a behavior characteristic of a normal ferroelectric whereas when x> 1 mol%, there is a small displacement of the temperature of maximum dielectric permittivity (Tm) with the frequency, indicating the existence of a typical behavior of a relaxor ferroelectric material. The Raman spectroscopy results suggest that La3+ ions tend to preferentially occupy the Bi3+ site in the peroviskite layer when x <1.0 mol%, whereas when x> 1.0 mol%, the process of incorporation occurred also in the Bi3+ site of the Bi2O2 layer. According to the analysis of XANES and XPS spectra, the local structure of atoms and electronic structure of Ti, Bi and La atoms of BLTx samples are not affected significantly by the addition of lanthanum. For samples of BLExT and BLTEx systems, the XRD data shows only the presence of a secondary phase in the x = 0.04 and 0.06 mol% compositions of the BLTEx system. The sintering at 1115 °C allowed to obtain samples presenting a relative high density than the sample BLT075 undoped sample. The addition of Er3+ induces significative changes in grain morphology by decreasing the average size of grains in the BLExT system and by increasing the BLTEx system. Through electrical measurements, it was observed a decrease in the Tm value in both cases. In the BLExT system, when x> 0.02 mol%, the behavior of Tm is dominated by the solubility limit. According to the XAS data, the local and electronic structure of Ti and Er atoms are not affected significantly by the addition of erbium.

Pós nanocristalinos de Ba1-xCaxTiO3(0&#8804; x &#8804; 0.30) foram sintetizados pela primeira vez por meio do método dos precursores poliméricos modificados, em temperaturas relativamente baixas (500°C). Para a densificação dos corpos cerâmicos duas técnicas distintas foram utilizadas: a sinterização convencional, utilizando um forno elétrico; e a sinterização a laser, na qual um laser de CO2 foi utilizado como principal fonte de calor. Os corpos cerâmicos sinterizados pelas duas técnicas apresentaram um tamanho médio de grãos em torno de 500 nm, porém uma maior densidade relativa foi obtida nas cerâmicas sinterizadas a laser, chegando a 99%, além de boa transparência, &#8764;42% a 940 nm para a amostra com 30 mol% de Ca com espessura de 0.5 mm. Também verificamos por meio de simulação numérica, que a equação de condução de calor na aproximação linear, considerando uma fonte de calor com perfil gaussiano, descreve qualitativamente o comportamento observado durante a sinterização a laser no seu estágio final. Por meio da técnica de espectroscopia de impedância foi feita a caracterização dielétrica dos corpos cerâmicos, nos quais três pontos principais foram estudados: i) o efeito do tamanho de grãos; ii) a influência da concentração de Ca; e iii) a influência do método de sinterização. Com a variação do tamanho do grão foram observadas mudanças na intensidade do pico de transição ferro-paraelétrica, na temperatura de Curie e na permissividade relativa à temperatura ambiente. Para concentrações de Ca até 15 mol%, as cerâmicas apresentaram uma transição de Curie estreita semelhante ao BaTiO3,enquanto que para concentrações maiores, uma transição de fase difusa foi observada. A sinterização a laser resultou em corpos cerâmicos com constante dielétrica 30% maior, e menor perda dielétrica do que as cerâmicas sinterizadas convencionalmente. Finalmente, foi proposto um modelo baseando-se na formação de vacâncias de oxigênio para o aumento da condutividade elétrica com a substituição de Ca. / Ba1-xCaxTiO3 (0 &#8804; x &#8804; 0.30) nanocrystalline powders were successfully synthesized for the first time at relative low temperature (500 °C) by a modified polymeric precursor method. The densification of the ceramics was made by two distinct techniques: conventional sintering using an electric furnace; and by a laser sintering process in which a CO2 laser is used as the main heating source. It was achieved dense ceramics with an average grain size about 500 nm from both techniques. However, the laser sintered ceramics presented a higher relative density (99 %) and a transparency of 42% at 940 nm in the sample with 30 mol% of Ca. By numerical simulation of the thermal conduction equation on the linear approximation case and taking account a thermal source with a gaussian profile, it was possible to describe qualitatively the final stage of the laser sintering process. The dielectric characterization of the ceramic bodies were carried out by the impedance spectroscopy technique and three main effects were studied: i) the grain size effect; ii) the Ca concentration influence; and, iii) the sintering technique influence. Modifying the grain size led to changes in the ferro-paraelectric transition magnitude, on the Curie temperature value and in the relative permittivity at room temperature. For Ca2+ concentrations up to 15 mol% the sintered ceramics presented a sharp Curie transition like BaTiO3,while for higher Ca concentrations a diffuse phase transition was observed. The laser sintered ceramics presented a dielectric constant 30% higher than the conventional sintering and a lower dielectric loss. Finally, we have proposed a model based on the oxygen vacancies formation to explain the conductivity increase with the Ca2+ substitution.

O presente trabalho teve como objetivo o estudo das propriedades elétricas e estruturais das amostras cerâmicas pertencentes ao sistema Ba1-xRxTi1-yZryO3 (R=Ca,Sr). As amostras na forma de pó micro ou nanoestruturadas foram respectivamente obtidas através do método de mistura de óxidos e do método dos precursores poliméricos. Amostras cerâmicas apresentando grãos em uma escala micrométrica foram obtidas através do método tradicional de sinterização em alta temperatura enquanto amostras cerâmicas nanoestruturadas foram obtidas através da técnica de sinterização por plasma (Spark plasma Sintering ou SPS). Os resultados obtidos através da técnica de espectroscopia de impedância mostraram que com o aumento da quantidade de Zr na matriz as amostras passam de um estado ferroelétrico normal para um estado ferroelétrico relaxor e que este efeito é mais pronunciado nas amostras contendo cálcio. A partir dos resultados da difração de raios X em alta resolução, foi possível determinar os processos de transição de fase em função da substituição dos átomos de Ti por Zr além de identificar um processo de transição de fase espontânea na amostra contendo cálcio e 18 mol % de zircônia. Através das medidas do espectro de absorção de raios X e do espectro Raman foi possível mostrar que, independente da composição e da estrutura a longa distancia, apresentam certo grau de desordem local e que esta desordem local está principalmente associada ao fato do átomo de titânio estar fora de sua posição centro simétrica no octaedro TiO6 e que está desordem é comparável a observada no composto BaTiO3 tetragonal. A desordem química devido ao aumento da quantidade de átomos de Zr na matriz associada a esta desordem local levam ao aparecimento do estado relaxor. Finalmente, o estudo das amostras preparadas por SPS mostraram que é possível obter amostras de composição BaTi0,80Zr0,20O3 apresentando uma alta densidade e tamanho de grão nanométrico. Os resultados da espectroscopia de impedância destas amostras mostraram devido ao pequeno deslocamento da temperatura de máximo e do alargamento da curva de permissividade com a diminuição do tamanho de grão, não foi possível classificar essa amostra como apresentando um comportamento típico de um material ferroelétrico relaxor. / This work aimed to study the structural and electrical properties of ceramic samples belonging to the Ba1-xRxTi1-yZryO3 (R = Ca, Sr) system. The powder samples presenting a micro or nanosize were respectively obtained by using a mixture of oxides and by the modified polymeric precursor methods. Micrometer scale ceramic samples were obtained through the traditional method of sintering at high temperature while nano-sized particles ceramics were obtained using the spark Spark Plasma Sintering (SPS) technique. The results obtained using the technique of impedance spectroscopy showed that with an increasing amount of Zr in the matrix, samples change from a normal ferroelectric state to a relaxor ferroelectric state and that this effect is more pronounced in samples containing calcium. From the results of high resolution X-ray diffraction technique, it was possible to determine the phase transition processes due to the substitution of Ti atoms by Zr and, in addition, identify a process of spontaneous phase transition in the sample containing calcium and 18 mol% of zirconium. From the measurements of X-ray absorption Spectroscopy and Raman spectra it was possible to show that regardless of the composition and structure of long range order, the samples have some degree of local disorder and that this local disorder is primarily associated with the fact that the titanium atom being out of its symmetrical center position in the octahedron and is TiO6 disordered. This is comparable to the distorsion observed in tetragonal BaTiO3 sample. The chemical disorder due to the increase of Zr atoms in the matrix associated with this disorder is responsible of the occurrence of relaxor state. Finally, the study of samples prepared by SPS showed that it is possible to obtain samples with BaTi0,80Zr0,20O3 composition with a high-density and nanometeric grain size. The results of impedance spectroscopy on these samples show a small shift of the maximum temperature and a slight broadening of the permittivity curve with decreasing grain size. However, this result does not allowed to classify the samples as having a typical relaxor ferroelectric material behavior.

Les transformateurs piézoélectriques se positionnent aujourd'hui comme une alternative technologique séduisante face aux solutions classiquement utilisées pour la génération des plasmas froids. Leur haute permittivité, leur faible tension d’alimentation et leur capacité de miniaturisation en font une solution sérieuse et originale pour de nombreuses applications faibles puissances, notamment dans le domaine biomédical pour la stérilisation, le traitement de surface et la décontami-nation des instruments médicaux. Dans le cadre d'un fonctionnement en générateur plasma, la conversion électromécanique au sein du transformateur s’accompagne de pertes mécaniques et diélectriques, souvent converties en chaleur. À ces effets s'ajoute l’influence proprement dite de la décharge sur le comportement électrique du dispositif. L’évolution dynamique et fortement non-linéaire de la décharge entraine un comportement méconnu des grandeurs électriques. Par conséquent, l’étage d’alimentation du transformateur constitue un sujet d’étude au même titre que le transformateur lui-même. De plus, étant donné la configuration du processus de génération, qui positionne le matériau piézoélectrique comme source et siège de la décharge plasma, il devient nécessaire d’analyser la viabilité du dispositif. L’ionisation du milieu gazeux environnant le générateur provoque des effets électroniques complexes, susceptibles d’entrainer des dépôts de matière à la surface du matériau ou d’en éroder la surface. C’est dans ce cadre, à l’interface entre le génie électrique et la science des matériaux, que s’articule cette thèse. Une première partie est destinée au développement d’un outil de commande numérique du générateur par une boucle de verrouillage de phase, assurant sa continuité de fonctionnement face aux variations des conditions opératoires. Par la suite, une modélisation du générateur plasma dans des configurations proches des décharges à barrières diélectriques est effectuée ;des simulations permettent une estimation de la puissance de décharge à partir d’une identification expérimentale des paramètres du modèle. Dans un deuxième temps, nous cherchons à établir une corrélation entre la structure du matériau et ses propriétés électriques en s’appuyant sur une méthodologie de caractérisation multi-échelle, avant et après décharge plasma. L'étude se focalise principalement sur l'évolution en surface de la structure cristalline et la composition chimique, en liaison avec les propriétés fonctionnelles du transformateur après génération de la décharge. Enfin, une étude en température porte sur l’investigation des effets d’auto-échauffement du générateur dans ce mode de fonctionnement / Due to intensive development efforts during the past decade, piezoelectric transformers havebecome an attractive alternative solution compared to the con-ventionally used technologies forcold plasma generation. Their high efficiency, thin-shaped dimensions and low voltage supplymake them serious and original candidates for numerous low power applications, particularly inbiomedical field. Operating as a plasma generator, the electromechanical conversion within thetransformer is accompanied by mechanical and dielectric losses, often converted into heat. On topof these effects, the discharge is likely to influence the electrical behavior of the device. Thedynamic and highly non-linear evolution of the dis-charge leads to an unknown behavior ofelectrical properties. Consequently, the transformer supply stage is an active research subject inthe same way as the trans-former itself. Moreover, considering the configuration of the generationprocess, which positions the piezoelectric material as the source and the spot of the plasmadischarge, it becomes necessary to consider the viability of the device. The ioniza-tion of thegaseous environment surrounding the generator causes complex elec-tronic effects, which canlead to material deposition on the surface of the generator and thus modify or even degrade it. It iswithin this framework, at the interface between electrical engineering and material science, thatthis thesis is articulated. A first part is intended to develop a setup for numerical control of thedevice using a digital phase-locked loop to ensure its continuous operation in different operatingconditions. Subsequently, a model of the plasma generator in configurations close to dielectricbarrier discharges is proposed; Simulations allow an estimation of the discharge power from anexperimental identification of the model parameters. In a second part, we seek to establish acorrelation between the material structure and its electrical properties based on a multi-scalecharacterization methodology, before and after plasma discharge. The study focuses mainly onthe surface evolution in terms of the crystalline structure and the chemical composition, related tothe over-all properties of the piezoelectric transformer before and after discharge generation.Finally, a temperature study that concerns the investigation of the effects of self-heating of thegenerator in this operating mode is performed

Ce travail de recherche porte sur l'étude d'un nouveau matériau issu de la combinaison de deux oxydes perovskites ferroélectriques Sr2Ta2O7 et La2Ti2O7 ; la solution solide résultante est formulée selon (Sr2Ta2O7)100 x(La2Ti2O7)x (STLTO). Notre étude comprend la synthèse de poudres, la réalisation de céramiques, le dépôt de films minces et leur caractérisation structurale, morphologique, élémentaire, optique, diélectrique et ferroélectrique. L'objectif visé à moyen terme pour ce matériau est son intégration dans des dispositifs hyperfréquences miniatures et reconfigurables. Pour cela, sont recherchées des permittivités élevées, variables sous champ électrique, afin d'atteindre une accordabilité du matériau, puis une reconfigurabilité en fréquence des antennes, par exemple. L'analyse structurale par diffraction des rayons X a confirmé, par la variation linéaire des paramètres de maille, la formation de la solution solide pour les compositions x ∊ [0-5]. Les analyses diélectriques menées à basses fréquences (1 100 kHz) sur les céramiques STLTO ont montré des valeurs maximales de permittivité (375) et d'accordabilité (55 % à 3 kV/mm), associées à des tangentes de pertes faibles (0,01), pour la composition x = 1,65. Les mesures en hautes fréquences (200 MHz – 18 GHz) sont en accord avec les résultats obtenus en basses fréquences. Le dépôt de films minces par pulvérisation cathodique réactive, réalisé à partir d'une cible de composition x = 1,65, produit des films s'apparentant à la phase Sr2,83Ta5O15, ce qui dénote une perte en strontium. Cependant, à basses fréquences, les films présentent des permittivités relativement élevées (130) pour des pertes faibles (0,01) avec une accordabilité modérée (A = 14,5% à 340 kV/cm à f =100 kHz). Le dépôt de films minces oxynitrures (Sr,La)(Ta,Ti)O2N, réalisé en atmosphère réactive Ar + N2, mènent à des échantillons colorés ayant des permittivités élevées (jusqu'à 3000 environ), mais avec des pertes également élevées (jusqu'à 2) et sans accordabilité. Par ailleurs, l'étude de films SrTaO2N a montré que ces composés sont adaptés pour la décomposition de l'eau sous lumière visible. / This research focuses on the study of a new material resulting from the combination of two ferroelectric perovskite oxides Sr2Ta2O7 and La2Ti2O7; the resulting solid solution is formulating according to (Sr2Ta2O7)100 x(La2Ti2O7)x (STLTO). Our study includes the synthesis of powders, the realization of ceramics, thin film deposition and their structural, morphological, elemental, optical, dielectric and ferroelectric characterizations. The medium-term objective for this material is its integration into miniature and reconfigurable microwave devices. For this, high permittivity, variable under electric field, is required in order to achieve a tunability of the material, then a reconfigurability of the antennas, for example. Structural analysis by X-ray diffraction confirmed, by the linear variation of the cell parameters, the formation of the solid solution for the compositions x ∊ [0-5]. The dielectric analyzes carried out at low frequencies (1 - 100 kHz) on STLTO ceramics showed maximum values of permittivity (375) and tunability (55% at 3 kV/cm), associated with weak loss tangents (0,01), for the composition x = 1.65. The measurements at high frequencies (200 MHz – 18 GHz) are in agreement with the results obtained at low frequencies. The deposition of thin film by reactive sputtering, made from a target of composition x = 1.65, produces films similar at Sr2.83Ta5O15 phase, which denotes a loss of strontium. However, at low frequencies, the films have relatively high permittivity (130) for low losses (0.01) with moderate tunability (A= 14.5% at 340 kV/cm at f = 100 kHz). Deposition of oxynitride thin film (Sr,La)(Ta,Ti)O2N, carried out in Ar + N2 reactive atmosphere, leads to coloured samples having high permittivity (up to about 3000), but with equally high losses (up to 2) and without tunability. Moreover, the study of SrTaO2N showed that these compounds are suitable for the decomposition of water under visible light.

La croissance rapide du marché des télécommunications a conduit à une augmentation significative du nombre de bandes de fréquences allouées et à un besoin toujours plus grand en terminaux offrant un accès à un maximum de standards tout en proposant un maximum de services. La miniaturisation de ces appareils, combinée à la mise en place de fonctions supplémentaires, devient un vrai challenge pour les industriels. Une solution consiste à utiliser des fonctions hyperfréquences accordables (filtres, commutateurs, amplificateurs,…). A ce jour, trois technologies d'accord sont principalement utilisées : capacités variables, matériaux agiles ou encore MEMS RF. Dans le cadre de cette thèse, nous avons travaillé sur l’optimisation de dispositifs hyperfréquences reconfigurables en utilisant des couches minces ferroélectriques KTN et des diodes varactor. Nos premiers travaux étaient relatifs à l’optimisation des dispositifs hyperfréquences accordables à base de couche minces KTN. Dans ce sens, nous avons tout d’abord caractérisé le matériau KTN en basse et haute fréquence afin de déterminer ses caractéristiques diélectriques et ses caractéristiques en température. Nous avons ensuite réalisé des dispositifs hyperfréquence élémentaires tels des capacités interdigitées et des déphaseurs à base de KTN. Leurs performances ont alors été comparées aux mêmes dispositifs réalisés cette fois à base de la solution la plus utilisée BST. Bien qu’un léger avantage soit acquis à la solution BST, il n’en reste pas moins vrai que les résultats avec le matériau KTN sont très proches indiquant que cette voie peut également, après optimisation, apporter une alternative au BST. La seconde partie de nos travaux concerne la réalisation de filtres planaires accordables en fréquence à base de matériaux KTN et de diodes varactor. Nous avons ainsi réalisé deux filtres passe-bande accordables. Un premier filtre passe-bande de type « open loop » possédant deux pôles agiles en fréquence centrale et un second filtre passe-bande de type SIR rendant possible l’accord de sa fréquence centrale ainsi que de sa bande passante à partir de diodes varactor. Lors de la conclusion sur nos travaux, nous évoquons les suites à donner à ce travail et les perspectives. / The rapid growth of the telecommunications industry has led to a significant increase in the number of allocated frequency bands and a growing need for terminals providing access to an increasing number of standards while offering maximum services. The miniaturization of these devices combined with the implementation of additional functions has become a real challenge for the industry. The use of tunable microwave functions (filters, switches, amplifiers ...) appears as a solution to this issue. In this way, three main technologies are mainly used: variable capacitors, tunable materials and RF MEMS. Within the scope of this thesis work, our investigations focused on tunable microwave devices optimization through the use of KTN ferroelectric thin films and varactor diodes. The first part of our study deals with the optimization of tunable microwave devices based on KTN ferroelectric thin films. In this way, we initially characterized KTN material in low and high frequency to determine its dielectric properties and characteristics according to the temperature. Then, we designed basic microwave devices such as interdigitated capacitors and phase shifters based on KTN thin films. Their performances were then compared with BST solution. Despite results highlighting a slight advantage to BST solution, KTN material, after optimization process, could be a BST alternative solution. In a second part, our work focused on the realization of tunable planar filters based on KTN materials and varactor diodes. We made two tunable bandpass filters. The first one is a center frequency tunable bandpass two pole open loop filter and the second one is a center frequency and bandwidth tunable SIR bandpass filter using varactor diodes. Finally, we discussed follow-up to give to this work and outlooks.

Polymer-based piezoelectric and triboelectric generators form the basis of well-known energy harvesting methods that are capable of transforming ambient vibrational energy into electrical energy via electrical polarization changes in a material and contact electrification, respectively. However, the low energy conversion efficiency and limited thermal stability of polymeric materials hinder practical application. While nanostructured polymers and polymer-based nanocomposites have been widely studied to overcome these limitations, the performance improvement has not been satisfactory due to limitations pertaining to long-standing problems associated with polymeric materials; such as low crystallinity of nanostructured polymers, and in the case of nanocomposites, poor dispersion and distribution of nanoparticles in the polymer matrix. In this thesis, novel functional polymeric nanomaterials, for stable and physically robust energy harvesting applications, are proposed by developing advanced nanofabrication methods. The focus is on ferroelectric polymeric nanomaterials, as this class of materials is particularly well-suited for both piezoelectric and triboelectric energy harvesting. The thesis is broadly divided into two parts. The first part focuses on Nylon-11 nanowires grown by a template-wetting method. Nylon-11 was chosen due to its reasonably good ferroelectric properties and high thermal stability, relative to more commonly studied ferroelectric polymers such as polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)). However, limitations in thin-film fabrication of Nylon-11 have led to poor control over crystallinity, and thus investigation of this material for practical applications had been mostly discontinued, and its energy harvesting potential never fully realised. The work in this thesis shows that these problems can be overcome by adopting nanoporous template-wetting as a versatile tool to grow Nylon-11 nanowires with controlled crystallinity. Since the template-grown Nylon-11 nanowires exhibit a polarisation without any additional electrical poling process by exploiting the nanoconfinement effect, they have been directly incorporated into nano-piezoelectric generators, exhibiting high temperature stability and excellent fatigue performance. To further enhance the energy harvesting capability of Nylon-11 nanowires, a gas -flow assisted nano-template (GANT) infiltration method has been developed, whereby rapid crystallisation induced by gas-flow leads to the formation of the ferroelectric δʹ-phase. The well-defined crystallisation conditions resulting from the GANT method not only lead to self-polarization but also increases average crystallinity from 29 % to 38 %. δʹ-phase Nylon-11 nanowires introduced into a prototype triboelectric generator are shown to give rise to a six-fold increase in output power density as observed relative to the δʹ-phase film-based device. Interestingly, based on the accumulated understanding of the template-wetting method, Nylon-11, and energy harvesting devices, it was found that thermodynamically stable α-phase Nylon-11 nanowires are most suitable for triboelectric energy generators, but not piezoelectric generators. Notably, definitive dipole alignment of α-phase nanowires is shown to have been achieved for the first time via a novel thermally assisted nano-template infiltration (TANI) method, resulting in exceptionally strong and thermally stable spontaneous polarization, as confirmed by molecular structure simulations. The output power density of a triboelectric generator based on α-phase nanowires is shown to be enhanced by 328 % compared to a δʹ-phase nanowire-based device under the same mechanical excitation. The second part of the thesis presents recent progress on polymer-based multi-layered nanocomposites for energy harvesting applications. To solve the existing issues related to poor dispersion and distribution of nanoparticles in the polymer matrix, a dual aerosol-jet printing method has been developed and applied. As a result, outstanding dispersion and distribution. Furthermore, this method allows precise control of the various physical properties of interest, including the dielectric permittivity. The resulting nanocomposite contributes to an overall enhancement of the device capacitance, which also leads to high-performance triboelectric generators. This thesis therefore presents advances in novel functional polymeric nanomaterials for energy harvesting applications, with improved performance and thermal stability. It further offers insight regarding the long-standing issues in the field of Nylon-11, template-wetting, and polymer-based nanocomposites.

<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>

Les matériaux ferroélectriques présentant une permittivité diélectrique élevée et de faibles pertes diélectriques présentent un grand intérêt pour la réalisation de condensateurs et le stockage de l'énergie électrique. Les propriétés structurales et diélectriques influencent les paramètres ferroélectriques tels que la polarisation maximale du matériau Pm et la polarisation rémanente Pr sous l'effet d'un champ électrique appliqué Em. Ce mémoire propose d'étudier les propriétés structurales, diélectriques et ferroélectriques des céramiques dérivées de BaTiO₃ (BT) et SrTiO₃ (ST) ainsi que des films épais PVDF pur et composites tels que PVDF/BT et PVDF/BZT. Les céramiques ont été synthétisées par la méthode de la réaction solide et le procédé sol-gel. La substitution dans les sites-A ou les sites-B du matériau BaTiO₃ avec des cations tels que Ca ²⁺, Sr²⁺ and Zr⁴⁺ réduit la densité d'énergie électrique stockée Wd et augmente l'efficacité de stockage énergétique η. La céramique BaZr₀.₅Ti₀.₅O₃ (BZT0.5) présente l'efficacité de stockage énergétique la plus élevée (η=75%). La substitution dans les sites-A du matériau SrTiO₃ avec 40% de cations Ca²⁺ diminue la permittivité diélectrique (ε'∽200), mais cette permittivité est cependant plus stable sur une large gamme de fréquence [100 Hz-1 GHz]. La céramique Sr₀.₆Ca₀.₄TiO₃ préparée par voie sol-gel présente la densité d'énergie électrique stockée la plus élevée (Wd=0.149 J/cm³) sous l'action d'un champ électrique maximal élevé (Em=105 kV/cm). Les films épais à base de polymère PVDF ont été synthétisés par Spin-Coating. La permittivité diélectrique des films épais PVDF pur augmente avec l'apaisseur du film. L'incorporation de particules BT et BZT0.15 dans la matrice polymère PVDF augmente la permittivité diélectrique des films composites PVDF/BT (ε'=32 pour 30% de particules BT) et PVDF/BZT0.15 (ε'=32 pour15% de particules BZT). / Ferroelectric materials with a high dielectric permittivity and low dielectric losses are very attractive for the realization of capacitors and for electrical energy storage. To improve the electrical energy density Wd, the structural and dielectric properties influence the ferroelectric parameters such as the maximum polarization Pm and the remanent polarization Pr under an applied electric field Em. This manuscript proposes to study the structural, dielectric and ferroelectric properties of ceramics derived from BaTiO₃ (BT) and SrTiO₃ (ST) as well as pure PVDF thick films and composites such as PVDF/BT and PVDF/BZT. The ceramics were synthesized by the solid state reaction reaction route and the sol-gel process. The subsitution in the A-sites or B-sites of the BaTiO₃ material with cations such Ca²⁺, Sr²⁺ and Zr⁴⁺ reduces the electrical energy density Wd and increases the energy storage efficiency η. The ceramic BaZr₀.₅Ti₀.₅O₃ (BZT0.5) has the highest energy storage efficiency (η=75%). The substitution in the A-sites of SrTiO₃ material with 40% of Ca²⁺ cations reduces the dielectric permittivity (ε'∽200), but is more stable over a wide frequency range [100 Hz -1 GHZ]. The Sr₀.₆Ca₀.₄TiO₃ ceramic prepared by sol-gel process has the highest electrical energy density (Wd = 0.149 J/cm³) under an electrical field Em = 105 kV/cm. The PVDF thick films were synthesized by Spin-Coating. The dielectric permittivity of pure PVDF thick films increases when increasing the thickness. The addition of BT and BTZ0.15 particles in the PVDF polymer matrix increases the dielectric permittivity of the composite PVDF/BT thick films (ε'=32 for 30% of BT particles) and PVDF/BZT0.15 ones (ε'=32 for 15% of BZT particles).