This work reports the production of microlamps and their structural properties after modifications induced by the heating process. Their production consists on films deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) and sputtering over silicon substrates. The filament, composed by a thin chromium wire, is protected against oxidation by a top thin layer. Four different materials were used as protective layer: SiC, SiO x N y , AlN and TiO 2 . The protective film is heated by the metallic filament and their chemical and structural properties may change, depending on the time interval and intensity of the applied current (up to 2h and 50mA). X-ray absorption near edge spectroscopy (XANES) measurements allowed investigating changes on the properties of the microlamps protective films heated under different polarization conditions. The LUCIA beam line of the synchrotron SOLEIL has a microfocus spot (3x3μm), permitting to evaluate the small thermally affected zone. The results showed that the SiO x N y film is thermally stable with negligible changes on the XANES spectra. A slight AlN oxidation is observed as heating rises, which is particularly evident for the sample heated at extreme conditions. TiO 2 XANES spectra showed that the material is crystallized with rutile structure and is also thermally stable. SiC thin films were widely affected, showing an oxidation process as the time interval and intensity of the current increased. In addition, once the films were deposited over the Cr filament, their XANES spectra are quite different from the standard sample (deposited over Si), even for the non-polarized microlamp, indicating a Cr contamination on the SiC structure.

Beijo pouco, falo menos ainda. Mas invento palavras que traduzem a ternura mais funda E mais cotidiana. inventei, por exemplo, o verbo teadorar. Intransitivo Teadoro, Teodora.

This thesis presents a study about the structure of thin films, deposited to be a protection layer against oxidation of microlamps, as well as chemical and structural modifications induced by their heating under operation. The studied microlamps were produced in the Group of New Materials and Devices (GNMD) of POLI-USP, having applications in microelectromechanical systems. They were produced by Plasma Enhanced Chemical Vapor Deposition (PECVD) and sputtering, over silicon substrates. The analyzed protection layer is a film on top of a small Cr filament. Four different materials were used as protection layer: a-SiC, a-SiO x N y , AlN and TiO 2 . The intensity and time interval of the electric current applied in the device were varied (up to 50 mA and during 10 s to 1,0 h). The beamline LUCIA of the SOLEIL synchrotron (France), that was used in this work, has a microfocus beam (3 ◊ 3 µm 2 ), allowing the evaluation of the micro region thermally affected, exactly on top of the filament, using X-ray absorption spectroscopy (XANES). The results demonstrated that the a-SiO x N y and TiO 2 (rutile) films are the indicated ones for this application, because, besides their thermal stability, they dissipate less heat. The AlN and a-SiC protective films showed structural changes caused by the heating related to the device operation. To improve the studies of these materials additional thin films samples, deposited over ordinary large flat substrates, were produced and analyzed by X-Ray Absorption Spectroscopy (XANES and EXAFS region), Grazing Incidence X-Ray Fluorescence (GIXRF) and Rutherford Backscattering Spectroscopy (RBS). A small oxidation was detected in the AlN films with the increase in temperature and these films presented a beginning of crystallization process with higher currents. The a-SiC films showed an intense and increasing oxidation as the intensity and duration of the applied current in the microlamps were raised. In addition, structural differences in the a-SiC film were observed in the micro area over the filament, compared with a reference film deposited over Si. The results achieved with the additional thin films revealed the diffusion of Cr and O into the a-SiC. Theoretical XANES spectra of a-SiC structures, constructed by molecular dynamics, were calculated by the Finite Difference Method Near Edge Structure (FDMNES) code, aiming to study the modifications induced by the presence of Cr and O into the material. The conclusion was that the microlamp design induced the grown of PECVD silicon carbide far from the best conditions, probably due to the presence of a cavity under the filament that reduced the substrate temperature during the deposition. This situation may have enhanced the Cr and O diffusion into de silicon carbide resulting in the structural changes observed.