Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 121-124). Also available via the Internet.

Os objetivos deste trabalho foram a implantação e a otimização da técnica de sinterização por varredura a laser de filmes espessos, o estudo da cinética do processo e a avaliação das propriedades do composto BaTi0.85Zr0.15O3 (BTZ) sinterizado a laser, em comparação com os filmes sinterizados em forno. Pós nanocristalinos de BTZ foram sintetizados em baixas temperaturas com sucesso pela primeira vez (600ºC), por meio do método dos precursores poliméricos modificado. Foram obtidos pós nanométricos com tamanho de partículas primárias de ~20 nm e com aglomeração controlada, uma inovação para pós de BTZ preparados por rotas químicas. Para a deposição dos filmes, a estabilidade das suspensões de partida foi estudada e filmes espessos com excelente homogeneidade foram depositados utilizando a técnica de eletroforese (EDP). O desenvolvimento da técnica permitiu o controle da espessura do filme a partir dos parâmetros de deposição. A montagem experimental para a sinterização a laser foi otimizada de modo a permitir a sinterização de filmes com dimensões de até 70 mm de comprimento por 10 mm de largura e espessuras variáveis. Os tempos de patamares em cada etapa foram dependentes da velocidade e do número de varreduras. A temperatura máxima que se pode atingir no filme espesso, durante cada varredura e para uma potência nominal do laser fixa, foi correlacionada com a densidade relativa. Os processos térmicos envolvidos durante a varredura a laser atuaram de modo similar á sinterização em duas etapas (two step sintering). Com o intuito de melhorar a densificação dos filmes, passamos a adicionar o composto Bi4Ti3O12 (BIT) (1 e 2 mol %) ao BTZ durante a deposição. A utilização do sistema desenvolvido para a sinterização por varredura a laser em conjunto com o acréscimo do aditivo BIT resultou em uma diminuição no tamanho de grão dos filmes e uma importante diminuição da porosidade aparente. Para a aditivação com 2 mol% de BIT obtivemos filmes de ótima densidade (porosidade aparente de ~4%) e reduzido tamanho de grão (~200 nm), resultado inédito em se tratando de filmes espessos. A sinterização a laser resultou em filmes com maior permissividade dielétrica em relação ao filme sinterizado em forno elétrico. As reações que ocorrem entre o BTZ e o BIT foram exploradas usando conjuntamente as técnicas de espectroscopia de impedância, análise térmica e difratometria de raios-X. / The goals of this work were the implantation and optimization of the technique of sintering by laser scan of thick films, the kinetic study of the process and the evaluation of the physical properties of the laser sintered compound BaTi0.85Zr0.15O3 (BTZ), compared to thick films sintered in conventional furnace. Nanocrystalline powders of BTZ were for the first time, successfully synthesized at low temperatures (600ºC) using the modified polymeric method. Nanometric powders with primaries particles of ~20nm sizes and controlled agglomeration were obtained which was an innovation for BTZ powders prepared by chemical methods. For the films deposition, the suspensions stability was studied and thick films with excellent homogeneity were deposited using the electrophoresis technique (EDP). The developing of the technique allowed the thicknesses control using the deposition parameters. The characteristics of the experimental apparatus were optimized in such a way as to allow the sintering of thick films whose dimensions were up to 70mm in length, 10mm in width and variable thicknesses. The step times in each stage were dependent on the velocity and scan number. The maximum temperature that can be achieved in the thick film, during each scan, and for a fixed rated laser power was correlated with the relative density. The related thermal process during the continuous laser scan acted in a similar way as a two-step sintering. To improve the densification of the films, we started to add the compound Bi4Ti3O12 (BIT) (1 e 2 mol %) to BTZ during the deposition. The utilization of the system developed for the sintering by laser scan alongwith the adding of the BIT resulted in a grain size decrease and a significant decrease in apparent porosity. For the 2mol% additivation we obtained films with excellent density (apparent porosity of ~4%) and reduced grain size (~200nm), which is an unpublished result for thick films. The laser sintering resulted in films with a higher dielectric permittivity in relation to the conventionally sintered film. The reactions between BTZ and BIT were explored using the techniques of impedance spectroscopy, thermal analysis and X-ray diffraction.

This work presents a method based on time domain techniques to characterize and model thick film inductor structures. The method is a time domain reflection (TOR) measurement which measures the input port's reflection transfer function of the component under test. The reflection from a short circuit is acquired as the reference waveform, while the reflection from the sample is acquired as the response waveform. From the information contained in both waveforms the complex impedance Z(jω) of the sample can be calculated. This information is used for modeling the inductor by fitting the data to a network model. This thesis also presents a technique for the modeling and the characterization of multilayer thick film inductors over the frequency range from DC to a few GHz. The modeling technique is based on the use of Time Domain Reflectometry (TDR) measurements to reveal the transmission structure equivalent network of the multilayer thick film inductor. The equivalent network model is then analyzed using a computer network analysis program to characterize the inductor performance. Other thick film inductor structures modeled in this work are: the spiral conductor is printed directly on the ceramic substrate, the spiral is printed on a ferrite layer, the spiral is printed on the substrate with the ferrite layer on top, and finally, two interconnected spiral layers sandwiching ferrite (or dielectric) layers. / M.S.

Inductors and transformers constitute two important magnetic components In RF and power hybrids electronic circuitry. Thick film inductors have been subject of extensive research in recent years because they significantly reduce the weight and size, and increase the frequency of operation of electronic circuits. The research work in this dissertation is aimed at the formulation of thick film ferrite pastes and ferrite epoxies and the design, construction, and evaluation of thick film spiral inductors. Wideband characterization (DC - 2GHz) of ferrite pastes, ferrite epoxies, and ferrite substrates is performed using two techniques. These techniques are based on current image and transmission line (coaxial cavity) concepts for low (DC-IOOMHz) and high (50MHz-2GHz) frequency regions, respectively. They are used to evaluate the permeability spectra of formulated and commercially available thick film magnetic materials in respective frequency ranges. A method to numerically calculate the inductance of thick film circular spiral inductors based on modeling the spiral as concentric circles is presented. A novel method for fine as well as coarse tuning of thick film inductors is also introduced. The tunable inductors are constructed using formulated ferrite epoxies and magnetic cores. The method of analysis of variance is used to investigate the variation significance of tunable inductors. Finally, chemical and mechanical properties of developed magnetic materials are discussed. The studied properties include, glass transition temperature, degradation temperature, thermal coefficient of expansion, adhesion, particle-size distribution and particle densification , grain size, and compositional constituents of the magnetic materials. / Ph. D.

Ceramic substrates play an important role in thick film hybrid microelectronic circuits. Existing substrates such as alumina and beryllia do not meet satisfactorily the desired requirements. The newly developed aluminum nitride (<i>AIN</i>) substrate shows a great deal of promise and potentially embraces the best qualities of alumina and beryllia. The objective of this dissertation is to study the electrical properties, thick film interaction, and environmental effects on <i>AIN</i> substrates, and also to examine the performance of this material for high power - high frequency hybrid thick film applications. In particular, wideband dielectric constant measurements of A1N and other ceramic substrates are performed, oxidization and humidity effects on surface properties of <i>AIN</i> are addressed, and short and long term aging effects on several circuit parameters are studied. To evaluate the performance of <i>AIN</i> in high power and high frequency applications, two circuits; an impulse generator and a power converter, are realized, tested and compared with those on alumina substrates. The thick film circuits realized on <i>AIN</i> perform considerably better than those on alumina. / Ph. D.

A new family of dielectric materials has been studied, individually as thick-film capacitors and as buried components incorporated in second-order lowpass and bandpass RC active filter circuits. The materials were electrically characterized in terms of the variation of dielectric constant and dissipation factor with frequency. The performance of the filter circuit is related to the characteristics of the dielectric materials. An analysis of the circuit is developed which accounts for the capacitor losses. / Master of Science

In the past decade, there has been an increased interest in magnetostrictive materials for micro actuators and sensors. Of particular importance are the Fe₂R intermetallics, where R = Tb, Dy. In this study, films of Tb[subscript 0.3]Dy[subscript 0.7]Fe[subscript 1.92] were prepared by three laser processing techniques (pulsed laser deposition, flat plate ablation and laser ablation of microparticles) to explore the effect of processing parameters on particle size, crystallinity and magnetic properties. The laser used in the experiments was a KrF laser with a 12 ns pulse width. Pulsed laser deposition of an alloyed target in vacuum produces dense amorphous films with the similar composition to the target, low coercivity (46 Oe) and good magnetostriction ([lambda][subcript two horizontal lines] = 305 ppm at 2300 Oe). Flat plate ablation and laser ablation of microparticles produced amorphous nanoparticles at 1 atm. The particles were subsequently jet deposited onto substrates to form thick films. Nanoparticle films produced by flat plate ablation resulted in oxidized and segregated particles due to extended, non-uniform plume expansion, laser target modification, and open porosity. Laser ablation of microparticles produced thick films with M[subscript s] = 13.8 emu/g. Two types of annealing treatments were performed to close porosity and increase Youngs modulus. Annealing of LAM films at temperatures up to 700°C in-situ and 950°C in a reducing atmosphere did not result in coarsening of the particles or crystallization of the Laves phase due to the core-shell structure of nanoparticles (rare earth oxide shell, Fe rich core) brought about by oxidation-induced segregation.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (doctoral)--VTT Micronova, 2006. / Includes bibliographical references. Also available on the World Wide Web.

Face à la raréfaction des énergies fossiles, l’industrie automobile se trouve dans l’obligation de réduire la consommation des véhicules. L’une des idées est de récupérer l’énergie perdue sous forme d’échauffements grâce à la thermoélectricité. L’objectif de ces travaux est l’implantation d’un module thermoélectrique au niveau du radiateur afin d’en récupérer la chaleur dans le cadre d’un projet de recherche financé par Valéo Systèmes Thermiques et l’ADEME. La conception des radiateurs nécessite des épaisseurs supérieures à la centaine de micromètres de matériaux thermoélectriques afin d’en optimiser l’espace disponible. L’électrodéposition est apparue comme la technologie la plus adaptée car elle permet de déposer les matériaux directement sur l’ailette. Cette étude est consacrée aux dépôts électrochimiques de chalcogénures de bismuth (Bi2Te3 et Bi0,5Sb1,5Te3), matériaux les plus performants aux températures de fonctionnement de l’échangeur thermique. La première partie de ces travaux concerne la faisabilité de l’obtention de films d’épaisseurs supérieures à 100 µm et leurs caractérisations : stœchiométrie, structures et propriétés thermoélectriques. L’utilisation originale d’une anode soluble permet l’obtention de films de Bi2Te3 de près de 400 µm. Pour le composé ternaire, la synthèse consiste en une succession de couches de composés différents (Bi0,25Sb0,75-Te0), avant de procéder à leur interdiffusion via un traitement thermique. La dernière partie concerne la réalisation d’un module thermoélectrique. Les multiples étapes de lithographie et de synthèses électrochimiques ont été étudiées afin d’obtenir un module adapté aux échangeurs thermiques. Les caractérisations préliminaires de leurs propriétés montrent des résistances élevées et plusieurs voies d’améliorations sont proposées / In order to face the rarefaction of fossil fuels, the automotive industry has to find new ways to reduce their vehicle consumption. One of the possible ideas is to recover the energy that is lost as heating by using thermoelectricity. The aim of this work is to set-up thermoelectric generators into the radiator in order to recover this lost heat in a frame of research project financially supported by Valéo Systèmes Thermiques and ADEME. The radiator design requires thermoelectric materials thicknesses up to hundred micrometers in order to optimize the available space. Electroplating seems to be the best way to synthesize those materials directly onto the radiator fins. This study focuses on the electroplating of the best thermoelectric materials adapted to the operating temperatures of the heat exchanger: bismuth chalcogenides (Bi2Te3 and Bi0,5Sb1,5Te3). Firstly, a study has been carried out in order to synthesize thick layers above 100 µm of those two materials. Stoichiometry and thermoelectric properties were also determined. The original use of a soluble anode permitted to obtain 400 µm thick Bi2Te3 films. For the ternary compound, the synthesis consisting in a succession of thin layers of Bi0,25Sb0,75 and Te0, before their interdiffusion by annealing, is also presented. Finally, the last part covers the study carried out on the realization of the thermoelectric generators. The multiple stages of lithography and electrochemical syntheses were studied in order to obtain a module adapted to the heat exchanger. The first characterizations evidence high internal resistances and different ways to improve them are also presented