Este artigo discute o emprego do carbeto de silício (SiC), na forma de substrato e filme fino, em sensores MEMS (Micro-Electro-Mechanical Systems) para aplicações em ambientes sujeitos a condições extremas, especialmente no setor aeroespacial. As propriedades físicas e químicas do SiC que o tornam um material adequado para dispositivos eletrônicos e sensores são descritas. Os conceitos, evolução e aplicações da tecnologia MEMS são apresentados. Uma visão geral sobre o estágio atual de desenvolvimento de sensores MEMS baseados em SiC e uma análise das pesquisas realizadas nesta área no exterior e no Brasil, tanto nas universidades quanto nas indústrias, são também apresentadas. Os recentes avanços alcançados, as dificuldades encontradas e o impacto dessas pesquisas são discutidos, bem como as perspectivas para um futuro próximo.

This paper discusses the use of silicon carbide (SiC), in bulk and thin-film form, in MEMS (Micro-Electro-Mechanical Systems) sensors for extreme environment applications, especially in aerospace. The physical and chemical properties of SiC that make it a suitable material for electronic devices and sensors are described. Concepts, developments and applications of MEMS technology are presented. An overview of the current stage of development of SiC-based MEMS sensors and an analysis of research conducted in this area in Brazil and abroad, both in universities and industries are also presented. The recent progress made, difficulties encountered and the impact of these investigations are discussed as well as the outlook for the near future.

A new dc hollow cathode plasma source has been assembled whith a conventional planar magnetron cathode used together with another plane cathode plate to form a hollow cathode cavity. The system comprises two cathode plates of aluminium separated by a distance d, one of them acting as target of the magnetron cathode, the other being an ordinary plate. The discharge anode is a metallic flange of the vacuum chamber. This leads to enhanced ionization in the cathode cavity region and enables the discharge to operate at significantly lower pressures than for a typical planar magnetron configuration. As a consequence, sputtered atoms can reach a substrate with minimum energy loss due to collisions with filling gas atoms. The discharge gas was a mixture of argon and nitrogen. AlN thin films were grown on silicon substrates, at ambient temperature, and characterized with respect to the structure and morphology by XRD and AFM analyses respectively. The structure and roughness of the AlN films were studied as a function of the deposition parameters.

The electrical breakdown has been investigated for low-pressure argon and nitrogen discharges under the influence of an external longitudinal magnetic field. Plane-parallel aluminum electrodes (5 cm diameter) separated by a variable distance d (4.0 cm < d < 11.0 cm) were sustained with a dc voltage (0 < V < 1 kV). A Helmholtz coil was used to produce an uniform magnetic field(B) parallel to the discharge axis. Paschen curves were obtained and the secondary electron emission coefficient (gamma), the first Townsend ionization coefficient (alpha) and the ionization efficiency(eta), were plotted with respect to the variation of the reduced field (E/P). To observe the effect of the magnetic field these curves were plotted for fixed values of B=0 and B=350 Gauss. As consequence of the longitudinal magnetic field, the free paths of the electrons in the Townsend discharge are lengthened and their lateral diffusion is reduced, thus reducing electron losses to the walls. The data presented in this paper give a quantitative description of the B-field effect on the Townsend's coefficients and overall it is concluded that the DC electrical breakdown of the gases is facilitated if a longitudinal magnetic field is applied along the discharge axis.

A theoretical and experimental study was developed about the applicability of a double probe system consisting of two directional Langmuir probes, both probes being located separately in a plasma column. The current- voltage characteristic of the double probe was obtained considering a plasma with a drifting maxwellian electron velocity distribution function and stationary ion background. In deriving the characteristic of the double probe, the plasma parameters, namely, electron temperature (Te), electron density (Ne), electron drift velocity (Vde) and plasma potential (Vp) are assumed to be non-uniform. The double probe characteristic is also dependent on the angle between the axial direction of the electron drift and the normal to the collecting area of the probe. Each probe can be rotated such that this angle can be varied between zero and 180 degrees. Various probe characteristics were simulated using plasma parameters obtained by independent single probe measurements in the positive column of a low-pressure arc discharge in mercury vapor. Typical parameters of the positive column, used in the simulation, are: Te = 5 eV, Ne = 10(17) m-3, v de = 8x10(5) ms-1. Experimental characteristics of the double probe were obtained and compared with the simulated results, showing good agreement. It is concluded that this directional probe system can be a reliable diagnostic tool especially for studies of non-uniform plasmas.