En aquest treball s'ha establert una metodologia d'anàlisi i caracterització del comportament tèrmic, mecànic i termomecànic d'estructures micromecanitzades per a sensors de gas a través de la combinació de simulacions numèriques i tècniques de caracterització de microsistemes (mesures electro-tèrmiques, termografia, nanoindentació, AFM, XRD, microscopia confocal, Auger).L'estudi del comportament tèrmic de les estructures micromecanitzades ha permès obtenir les característiques bàsiques que controlaran el comportament del sensor, com són el consum en potència, la distribució de temperatura i el temps de resposta del substrat. L'anàlisi termomecànic ha consistit en determinar els esforços residuals en cada estructura així com l'estudi de la deformació dels diferents dissenys per a diferents temperatures de treball. S'han identificat diferents mecanismes de degradació en els materials que formen els sensors i s'ha obtingut el comportament termomecànic fins la ruptura del sensor. Tant en l'estudi tèrmic com en el termomecànic, la interacció entre la capa sensora i el substrat micromecanitzat així com l'influencia del material sensor en el comportament global del dispositiu han estat aspectes investigats.El treball inclou, a més, la caracterització termomecànica del Pt-Ti emprat en estructures micromecanitzades a través de la utilització de mètodes de Nanoindentació, Microscopia de Forces Atòmiques (AFM), Difracció de Raigs X (XRD) i espectroscopia Auger. També inclou el desenvolupament d'una metodologia per predir la fatiga tèrmica en microsistemes basada en la combinació dels models elasto-plàstics de metalls en capa prima (Alumini, Pt-Ti) amb simulacions numèriques. Finalment, de la metodologia d'anàlisi electro-termo-mecànic que s'ha dut a terme, es poden obtenir regles de disseny per la implementació de microsistemes que treballin en diferents règims de temperatura i en concret, directament aplicables al disseny i fabricació d'estructures micromecanitzades per a sensors de gas / This work presents a complete thermomechanical study of different micromachined gas sensor substrates based on closed and suspended membrane microstructures. The work has been carried out combining coupled electro-thermo-mechanical three-dimensional finite element method simulations with different experimental techniques such as those used in Microsystems characterization (thermo-electrical, thermography, AFM, XRD, confocal microscopy, Auger..). The performances predicted by simulations, such as the power consumption, the temperature distribution, the time response, the membrane deflection during operation and the preferential failure sites in the micromachined substrates have been confirmed by experience. The work includes the thermo-mechanical characterization of Pt-Ti thin films used in the structures using Nanoindentation, AFM, XRD and Auger spectroscopy. Additionally, a methodology to predict the thermal fatigue in microsystems, which combines experimental thin metal elasto-plastic models (Al, Pt-Ti) and coupled thermo-mechanical FEM simulations, has been developed.The good agreement between simulations and experimental results validates the numerical models, and allows us to consider the adaptability of the analyzed designs as micromachined substrates for integrated gas sensors.Keywords: MEMS, Microsystems, gas sensors, thermal fatigue, Al, Pt-Ti, FEM. / En este trabajo se ha establecido una metodología de análisis y caracterización térmica y termomecánica de estructuras micromecanizadas en silicio para aplicaciones en sensores de gas. Esta investigación ha combinado simulaciones numéricas mediante el método de los elementos finitos con técnicas experimentales de caracterización utilizadas en el campo de los microsistemas (medidas electro-térmicas, termografía, AFM, XRD, microscopia confocal, Auger).El estudio térmico de dichas estructuras ha permitido obtener su consumo en potencia, la distribución de temperaturas, la dinámica térmica, así como ha permitido fijar con precisión las propiedades térmicas de los materiales típicamente utilizados en la tecnología de los microsistemas. El estudio mecánico ha permitido obtener los esfuerzos residuales inducidos por los procesos de fabricación. Además, se ha obtenido la deformación de las estructuras a diferentes temperaturas de trabajo hasta la ruptura total de las membranas. Durante las altas temperaturas de trabajo se han detectado y analizado diferentes mecanismos de degradación en los materiales. El trabajo incluye además, la caracterización termo-mecánica del Pt-Ti depositado por sputtering, ampliamente utilizado en microsensores de gas, mediante el empleo de técnicas de Nanoindentación, Microscopia AFM, Difracción de Rayos X (XRD) y espectrocopia Auger. También presenta el desarrollo de una metodología para la predicción de la fatiga térmica en microsistemas, que se basa en la combinación de modelos elasto-plásticos para metales en capa delgada con simulaciones numéricas.Finalmente, de la metodología de análisis termo-mecánico que se ha llevado a cabo, se pueden obtener reglas de diseño para microsistemas que trabajen a diferentes temperaturas, y en concreto directamente aplicables al diseño y fabricación de estructuras micromecanizadas para sensores de gas. Palabras clave: MEMS, microsistemas, sensores de gas, fatiga térmica, Al, Pt-Ti, MEF.

In this study, barium strontium titanate (BST) thin films with different compositions (Ba0.9Sr0.1TiO3, Ba0.8Sr0.2TiO3, Ba0.7Sr0.3TiO3, Ba0.5Sr0.5TiO3) were produced by chemical solution deposition technique. BST solutions were prepared by dissolving barium acetate, strontium acetate and titanium isopropoxide in acetic acid and adding ethylene glycol as a chelating agent and stabilizer to this solution, at molar ratio of acetic acid/ethylene glycol, 3:1. The solution was then coated on Si and Pt//Ti/SiO2/Si substrates at 4000 rpm for 30 seconds. Crack-free films were obtained up to 600 nm thickness after 3 coating &amp / #8211 / pyrolysis cycles by using 0.4M solutions. Crystal structure of the films was determined by x-ray diffraction while morphological properties of the surface and the film-substrate interface was examined by scanning electron microscope (SEM). Dielectric constant, dielectric loss and ferroelectric parameters of the films were measured. Sintering temperature, film composition and the thickness of the films were changed in order to observe the effect of these parameters on the measured electrical properties. The dielectric constant of the films was decreased slightly in 1kHz-1 MHz range. It was seen that dielectric constant and loss of the films was comparable to chemical solution deposition derived films on literature. Maximum dielectric constant was obtained for the Ba0.7Sr0.3TiO3 composition at a sintering temperature of 800&amp / #730 / C for duration of 3 hours. Dielectric constant increased whereas dielectric loss decreased with increasing film thickness. BST films have composition dependent Curie temperature. For Ba content greater than 70 %, the material is in ferroelectric state. However, fine grain size of the films associated with chemical solution deposition and Sr doping causes the suppression of ferroelectric behaviour in BST films. Therefore, only for Ba0.9Sr0.1TiO3 composition, slim hysteresis loops with very low remanent polarization values were obtained.

ABSTRACT PREPARATION OF PLZT THIN FILMS BY CHEMICAL SOLUTION DEPOSITION AND THEIR CHARACTERIZATION Kaplan, Burkan M.S., Department of Metallurgical and Materials Engineering Supervisor: Prof. Dr. Macit &Ouml / zenbaS November 2005, 125 pages In this study, La3+ was substituted into lead zirconate titanate (PZT) system by Pb1-xLax(ZryTi1-y)1-x/4O3 nominal stochiometry and it was processed via chemical solution deposition on (111)-Pt/Ti/SiO2/Si-(100) substrate.PLZT solutions were prepared by mixing two solutions, one of which was obtained by dissolving lead acetate and lanthanum acetate hydrate in 2 methoxyethanol at high temperature. This solution was then mixed with the second solution containing zirconium propoxide and titanium isopropoxide. 40ml/0.4M solution was prepared and spin coated on Pt/Ti/SiO2/Si substrates at 3000 rpm for 30 seconds. After 4 coating cycles, film thickness was reached to 600 nm. A systematic study was carried out in different regions of PLZT phase diagram tetragonal, rhombohedral and on the morphotropic phase boundry (MPB) to obtain optimized results of ferroelectric, dielectric and optical properties of the material. During the period of the work, effect of parameters on these properties such as heat treatment conditions, chemical composition of the film, microstructure and thickness of the film was investigated. The films were characterized structurally and electrically. For structural properties, X-ray diffraction technique (XRD), energy dispersive spectrometry (EDS) and Scanning Electron Microscope (SEM) were used to observe phases and surface characterization. For electrical measurements, ferroelectric tester was used to obtain dielectric constant, loss tangent and hysteresis curves. Optical transmittance of the films was also investigated by UV-VIS Spectrophotometer and optical film constants were calculated by modified envelope method. It was observed that the optimum heat treatment conditions were achieved at 7500C for 3 hours. The highest ferroelectric and dielectric properties such as remanent polarization and dielectric constant were obtained using that temperature. The dielectric constant of the films was measured in the frequency range of 1kHz-1MHz and remained almost constant in this region. The change of dielectric constant and ferroelectric hysteresis loops were obtained as a function of Zr/Ti ratio and La content. The grain size as a function of sintering temperature and La content was investigated. It was seen that as the sintering temperature was increased, the grain size of the films increased. The same tendency was also observed when the La content was increased. Fatigue behavior of PLZT thin films was also investigated by Radiant Ferroelectric Tester at 50 kHz and &plusmn / 15V. Change of remanent polarization (Pr) as a function of cumulative switching cycles (N) was drawn with the log scale of x-axis. Furthermore, leakage current characteristics of the films were also obtained by the ferroelectric tester at &amp / #61617 / 15V. It has been observed that as the La content of the film was increased, leakage current of the PLZT films decreased. Keywords: PLZT, (111)-Pt/Ti/SiO2/Si-(100) substrate, Chemical Solution Deposition.

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