H2S sensing properties of noble metal doped WO3 thin film sensor fabricated by micromachining

The purpose of this research is to develop a semiconductor-type H2S gas sensor with silicon-based microfabrication and micromachining technology. This successful approach allows for the production of small, geometrically well-defined sensors that are reliable and mechanically robust, and is compatible with VLSI processes. Individual sensor cost is also greatly reduced because the sensors are batch fabricated. The main sensing region is covered with a 300 μm×300 μm WO3 thin film, which is deposited by RF sputtering on silicon wafer substrate. Platinum (Pt), gold (Au) or Au-Pt noble metals was then deposited onto WO3 thin film as activator layer by sputtering. Under 1 ppm H2S and at an operating temperature of 220 °C, the individual sensitivities of the Pt and the Au-Pt doped WO3 gas sensors are 23 and 5.5, respectively. The sensor response times of Pt, Au-Pt and Au doped WO3 thin films are 30, 2 and 8 s, respectively, and the recovery times are about 30, 30 and 160 s, respectively. The results show that the Pt doped WO3 gas sensor exhibits acceptable response time, recovery time and as well as a high sensitivity.