This work describes the design, simulation, fabrication and characterization of a TiN/Pt microheater prepared on GaAs
micromechanical structure as a prospective device for MEMS gas sensor array. We use the electro-thermal simulation to
verify the properties of the designed microstructure, which conformed achievement of the operating temperatures in the
range of 200 to 320°C with heating power less than 25 mW. The average temperature gradient in the active area does not
exceed 0.6 K/μm. We demonstrated the fabrication of GaAs suspended membranes, realized in two steps, by
combination of surface and bulk micromachining. We also describe the development and characterization of a
microheater on a GaAs membrane. The power consumption at an operating temperature of approximately 550 K is about
30 mW and the achieved thermal resistance value is 8.43 K/mW.
Bismuth film electrodes (BiFEs) have a potential to replace toxic mercury used most frequently for determination of
heavy metals (Cd, Pb, Zn) by anodic stripping voltammetry. We prepared a graphite disc electrode (0.5 mm in diameter)
from a pencil-lead rod and developed a nitrogen doped diamond-like carbon (NDLC) microelectrode array consisting of
50 625 microdiscs with 3 &mgr;m in diameter and interelectrode distances of 20 &mgr;m on a highly conductive silicon substrate
as a support for BiFEs. The disc graphite BiFE was used for simultaneous determination of Pb(II), Cd(II) and Zn(II) by
square wave voltammetry (SWV) in an aqueous solution. We found the optimum bismuth-to-metal concentration ratio in
the solution to be 20. The dependence of the stripping responses on the concentration of target metals was linear in the
range from 1×10<sup>-8</sup> to 1.2×10<sup>-7</sup> mol/L. Detection limits 2.4×10<sup>-9</sup> mol/L for Pb(II), 2.9×10<sup>-9</sup> mol/L for Cd(II) and 1.2×10<sup>-8</sup> mol/L for Zn(II) were estimated. A bismuth-plated NDLC microelectrode array was used for Pb(II) determination by
differential pulse voltammetry (DPV) in an aqueous solution. We found that the stripping current for bismuth-plated
NDLC array was linear in the concentration range of Pb(II) from 2×10<sup>-8</sup> to 1.2×10<sup>-7</sup> mol/L. The detection limit 2.2×10<sup>-8</sup>
mol/L was estimated from a calibration plot.
In the field of micromachining dry etching processes of silicon are getting more and more important in view of applications. By means of RIE processes it is possible to achieve structures with a very high aspect ratio. This is interesting especially in comparison with the well known but expensive LIGA technique. Unfortunately the anisotropy of the profile in silicon depends strongly on different process conditions. Therefore experiments were carried out with variations in the gas composition, the plasma power and the mask materials. All investigations were made in a 310-type machine from STS. The gas composition was made of SF<SUB>6</SUB>, O<SUB>2</SUB> and CHF<SUB>3</SUB>. The flow rate of these gases was varied in a wide range. The power of the plasma was hanged from 75W up to 600W at a frequency of 13,56MHz. Aluminium, copper, nickel and chromium were used as masking materials. The width of the patterns was in a range of > 20 micrometers. In contradiction to results known from literature it was not simple to achieve structures with vertical sidewalls. Using aluminium as materials, the sidewalls were rounded independent of the power and the composition of the gas. In some cases a small redeposition was observable at the bottom of the structures. A kind of microgas was observed, too. Copper showed high etch rates in some gas compositions and at defined power conditions. Therefore a complete removing of the masking layer was observed in some cases. Some material was redeposited in the transition zone between the sidewalls and the bottom. The structures showed rounded edges and no vertical sidewalls. A higher redeposition rate was found using nickel as masking material. Unfortunately this redeposition occurred at the bottom of the structures. This is measurable in a decrease of the etch rate. The structures are rounded with a kind of vertical sidewalls. Anisotropic structures with vertical sidewalls were observed with chromium as mask layer. The anisotropic etch behavior with a high aspect ratio was achieved only in a small range of the gas composition and the plasma power.