A surface micromachined polysilicon membrane, compatible with IC technology, was technologically designed and mechanically and thermally simulated by 3D finite element 'COSMOS' program in order to investigate its capability to work as micro hot plates for gas sensing applications. The optimized lay-out of hot plate consists of a polysilicon membrane of area of 110 by 110 micrometers 2 supported by four 'poly' suspended bridges and a central 'poly' pillar (MWCP). The air gap between membrane and substrate is equal to 1 micrometers . Within this paper, the simulation results are shown as a function of input power and surface area of the membrane. At room temperature the following results were obtained. The maximum normal stress has a value of 151.12 N/m2 and is situated at a distance of 20 micrometers around the central pillar. Also, the maximum displacement has a value of 3.81 by 10-4 micrometers and it is located at about half distance between the center of the membrane and its lateral edge. At an input power of 100 mW applied to the MWCP structure, the strain-stress spatial distributions have been qualitatively preserved with respect to RT situation but all the values increased by about 1300 times. The value of this normal stress for the MWCP structure is now about 196.45728 by 103 N/m2. For an input power of 100 mW, the maximum displacements of the membrane are located in the same place as in the RT case, and their values are lower than 0.1 micrometers .
This paper present the results from the investigation of the chemical anisotropic etching of single-crystal silicon in the following solutions: KOH, K3[Fe(CN)6] 0.1M, K4[Fe(CH)6] 3H2O 0.1M, KNO3 0.1M and/or complexant added. The complexants added in KOH solution were: Calix(4)arenes, Phenols and Ether Dibenzo 18 Crown 6. The result using also NaOH or LiOH H2O and complexants are presented. The reaction mechanism and the hillocks formation and elimination are analyzed. The results allow us to use the redox system and/or the organic complexants, to monitor the etching process, to obtain a smooth silicon surface, almost free of hillocks, to utilize the usual mask material resistant at the new etchants.
Sol-gel organic synthesis of SnO2 thin films from tin ethoxide precursor is reported here as a promising and cheap alternative of the 'classical' chemical and physical preparation methods of the SnO2 thin films, for gas sensing applications. A simple, integrated circuit compatible test structure, for rapid evaluation of the sensing properties of the SnO2 sol-gel derived thin films is described. The main features of our microstructure consists of a a heating resistor integrated on chip, made of highly boron doped silicon and a metallization system from Au/W deposited on a planarized chemically vapor deposited SiO2 layer. The SnO2 films have shown the well-known increase-maximum-decrease dependence of chemoresistance as a function of temperature, with a maximum at about 380 degrees C, when they are measured in clean, dry air. The sensitivity of SnO2 films to high concentration of H2 in air was studied within a quartz furnace, externally heated in the temperature range from 200 to 450 degrees C. The relative sensitivity is equal to 100 percent at temperatures as low as 200 degrees C, while its maximum value is anticipated to be above 450 degrees C. The CO sensing properties of SnO2 layers were evaluated as a function of input power applied on the integrated heating resistor. We have obtained relative sensitivities of 30 percent for 500 ppm CO concentration in dry air and an input power of 209 mW.
In this paper we present a new microdevice used for the anodic oxidation of organic compounds. It has as component parts an electrochemical micropump, 2 microreservoirs and a reaction chamber. the electrochemical micropump is electrochemical-pneumatic actuated, using an electrochemical generated gas as fluid motor. The volume of reaction chamber is 1.5 cubic mm and is equipped with working electrode, counterelectrode and reference electrode. Anisotropic etched silicon was used as construction material, Pt thick films and Ag/AgCl were used as electrode materials. Using this device, the anodic oxidation of 4-hydroxy-1,3- phenylendiammoniumdichlorid was performed.