Novel bi-functional film ceramic sensors for environmental applications

Abstract

Two types of bi-functional film sensors have been developed for environmental applications. The first sensing device is based on n-type semiconducting metal oxide WO/sub 3/ and is fabricated using thin-film surface microfabrication technology. It utilises gas chemisorption at elevated temperatures higher than 300/spl deg/C as well as water physisorption on grain surfaces at temperatures lower then 150/spl deg/C. Both humidity and particular pollution gases such as ozone, NH/sub 3/ and NO/sub 2/ can be detected with high sensitivity and selectivity. The Pt-film heater at the back side of the sensor serves also as a thermometer. The other sensor is composed of Cr/sup 3+/ doped porous perovskite Ba/sub 1-x/Sr/sub x/TiO/sub 3/ (x=0-1) and is fabricated using thick-film technology. It exhibits a change in dielectric constant with respect to temperature variations, while the electrical resistance is a function of humidity. Hence, temperature and humidity can be simultaneously and independently detected by measuring the sensor capacitance and the sensor resistance. Crosstalk between both sensing measurands is negligible.