LPCVD amorphous silicon carbide films, properties and microelectronics applications

This paper describes the deposition and properties of amorphous silicon carbide thin films, prepared by the low pressure chemical vapour deposition (LPCVD) technique at different temperatures (700-1000°C), using hexamethyldisilane as precursor. Films composition, morphology, structure and electric properties as a function of different deposition conditions were established. Two basic applications, such as the use of a-SiC films as etching mask layers for sensors silicon membrane fabrication and as active layers for field emission devices are reported and discussed in correlation with film properties. Silicon carbide films were patterned by dry etching process in a plasma barrel reactor, using CF4 + O2 as gas feed. The upper limits of the field emission current densities obtained from a-SiC layers were 2.4 mA/cm2 for the electric field of 25 V/µm

Voltammetric characterization of micro- and submicrometer-electrode arrays of conical shape for electroanalytical use

Densely packed micro- and submicrometer electrode arrays of platinum and gold (the nominal number, N, of electrodes in each array varies between 225 and 3600) are fabricated by photolithographic technique and vapor deposition processes of metal films. The electrodes are conical-shaped and only their apexes are exposed to the electrolytic solution. The electrode arrays are characterized electrochemically in Ru(NH3)6Cl3 aqueous solutions by using cyclic voltammetry at low scan rates, to establish the number of electrochemically active electrodes (Nac) in each array; the geometric characterization is performed by scanning electron microscopy. All the investigated arrays provide steady-state voltammograms, indicating diffusionally independent behavior of each microelectrode. The number of microelectrodes that are active in the fabricated arrays depends on microelectrode density. In particular, for the arrays with N = 3600 and N = 225, the fraction of active sites is about 45% and 90%, respectively. The analytical performance of some of the Pt version of the arrays is tested in hydrogen peroxide solutions, allowing verifying that linear calibration plots over the concentration range (0.1-20 mM) are obtained. This dynamic range is larger than that typically recorded at smooth polycrystalline platinum electrodes (0.5-5 mM), and the better performance is attributed to both the higher aspect ratio of the cone geometry and the higher mass transport associated to each microelectrode of the array. Reproducibility (within 3.5%, r.s.d.) and long-term stability (within 5%, r.s.d., after 8 h continuous use) of the electrode systems are satisfactory. A low detection limit, based on the signal to noise ratio equal to 3, of 0.05 mM is found, which is adequate for a rapid monitoring of H2O2 in real samples and industrial processes

Vacuum microdevices

In the paper MEMS-type microsystems working in vacuum conditions are described. All the benefits and drawbacks of vacuum generated in microcavities are discussed. Different methods are used to produce vacuum in microcavity of MEMS. Some bonding techniques, sacrificial layer method or getter materials are presented. It is concluded that the best solution would be to invent some kind of vacuum micropump integrated with MEMS structure. Few types of already existing vacuum micropumps are shown, but they are not able to generate high vacuum. As the most promising candidate for miniaturization an orbitron pump was selected. The working principle and novel concepts of its construction are described. The most important part of the micropump, used for gas ionization, is a field-emission electron source. Results of a research on a lateral electron source with gold emissive layer for integration with a micropump are presented