Novel bi-functional film ceramic sensors for environmental applications

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 WO₃ and is fabricated using thin-film surface microfabrication technology. It utilises gas chemisorption at elevated temperatures higher than 300°C as well as water physisorption on grain surfaces at temperatures lower then 150°C. Both humidity and particular pollution gases such as ozone, NH₃ and NO₂ 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 Cr³⁺ doped porous perovskite Ba_1-xSr_xTiO₃ (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