By combining structural and chemical thin film analysis with detailed plume diagnostics and\ud modeling of the laser plume dynamics, we are able to elucidate the different physical mechanisms\ud determining the stoichiometry of the complex oxides model material SrTiO3 during pulsed laser\ud deposition. Deviations between thin film and target stoichiometry are basically a result of two\ud effects, namely, incongruent ablation and preferential scattering of lighter ablated species during\ud their motion towards the substrate in the O2 background gas. On the one hand, a progressive\ud preferential ablation of the Ti species with increasing laser fluence leads to a regime of Ti-rich thin\ud film growth at larger fluences. On the other hand, in the low laser fluence regime, a more effective\ud scattering of the lighter Ti plume species results in Sr rich films

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Integration of new functional materials into silicon microsystems is a key factor to enable technology for a wide range of innovative MEMS devices. Piezoelectric materials are of primary interest for integrating sensing and actuation functions in MEMS due to their high forces and high energy densities. The use of PZT thin films in MEMS applications offers the possibility of increasing the sensitivity or actuation capabilities of the devices compared to alternatives such as AlN and ZnO. In general, PZT thin films exhibit smaller piezoelectric coefficients and polarizations than PZT bulk materials due to grain size, composition, crystallographic orientation, non-defined stoichiometry and mechanical boundary conditions. Moreover, PZT thin films are typically grown onto amorphous surfaces resulting in polycrystalline structures, which often lead to degraded performance due to fatigue and aging characteristics. Since epitaxial PZT films exhibit properties, including piezoelectric coefficients, polarizations, and dielectric constants, generally superior to polycrystalline films, it is of high interest to consider their application in MEMS devices, however, there are some real challenges to be solved. Once these issues are overcome, epitaxial PZT thin films could offer interesting potentials in the realization of high performance piezoelectric MEMS.In this thesis, several aspects related to the development of epitaxial piezoelectric MEMS on silicon are investigated, which cover the following topics: the deposition and integration of high quality epitaxial PZT thin films on silicon wafers; the establishment of microfabrication techniques with associated process flows; and the FEM supported design, and characterization of epitaxial piezoelectric MEMS. A short overview is first given on the current state-of-the-art of piezoelectric MEMS. The integration of epitaxial oxide films on silicon wafers and their properties is then briefly described. The epitaxial oxide thin film heterostructures are based on a piezoelectric Pb(Zr 0.2 Ti 0.8 )O 3 layer grown on 2″ silicon wafers through two oxide layers: SrTiO 3 used as buffer and metallic SrRuO 3 used as bottom electrode. The optimized microfabrication process for these oxide layers with specific attention in maintaining the piezoelectric properties of the epitaxial PZT films is presented. The polarization was measured to optimize their processing with at the end no degradation of the piezoelectric properties throughout the process. The epitaxial PZT thin films exhibit a large load. The second application is based on an epitaxial PZT membrane to produce a resonating device.The study of basic characteristics of such device has shown excellent results as it shows a strong harmonic oscillation response with a high quality factor at atmospheric pressure. The finite element model of the epitaxial PZT membrane has then been developed for localized-mass sensing application to determine the resonant frequency, and the effect of the position of the mass and of the resonant mode o...

The effect of ambient gas on the expansion dynamics of the plasma plume generated by excimer laser ablation of a LaMnO3 target is investigated by using fast photography. The plume propagation in an oxygen environment is examined with pressure ranging from vacuum to a few millibars. Imaging analysis performed over a complete set of images of the plume emission, for each pressure, has allowed following the changes in the plume structure, the plume front dynamics and stopping length, as well as the variation of plume angular distribution as a function of time and pressure. Our experimental findings evidence a number of interesting effects occurring at various times of the expansion and at different pressure levels. At low pressure (< 10(-2) mbar) the plume expands freely resembling the propagation in high vacuum condition. Then, at intermediate pressure levels (10(-2)-1 mbar) spatial splitting of the plume, plume front oscillations, plume broadening and sharpening, and, finally, plume stopping are observed as a function of the expansion time. The plume stopping length and the asymptotic angular width of the plume as a function of the pressure are analyzed and discussed. The expansion dynamics of the plume front is examined by means of a theoretical description of plume evolution and shock-wave propagation, which considers distance-related pressure dimensionless variables, resulting in a fairly good agreement