TIN OXIDE MICROSENSOR FOR LPG MONITORING

A silicon-based SnO2 gas sensor has been fabricated for monitoring liquified petroleum gas (LPG), commonly used as town gas. The gas sensor is made by silicon IC technology together with SnO2 thin-film processing. The whole chip with a size of 9 mm x 9 mm consists of nine sensors (three by three array). Each sensor is supported by a thin membrane of SiO2/Si3N4/SiO2 layers that provides a low thermal mass and prevents heat conduction through the surrounding substrate material. Tin oxide thin film is prepared by thermal evaporation of metallic tin granules and subsequent thermal oxidation of the metallic film at 600 degrees C. To form the SnO2(Pt) thin film, a layer of Pt with a thickness of several tens of angstroms is sputtered onto the tin oxide film and heat treated at 500 degrees C in air for several hours in order to stabilize its electrical response. The fabricated SnO7(Pt) microsensors exhibit about 85 and 92% sensitivities to 5000 ppm C3H8 and 5000 ppm C4H10 (the main components of LPG) at 250 degrees C, respectively, and show a rapid response time of less than 5 s.