HEATERS FOR GAS SENSORS FROM THICK CONDUCTIVE OR RESISTIVE FILMS

The temperature of gas sensors influences their sensitivity, selectivity and response time. Most of them are operated at significantly elevated temperatures (e.g. electrochemical sensors based on semiconducting metal oxides require up to 900-degrees-C). The possibility of using thick-film heaters in smart planar sensors is often reported. This paper, however, presents results of long-term high-temperature stability examinations of different resistor/conductor systems (in the temperature range 400-600-degrees-C) and several conductive films with different metallurgy (for temperatures between 600 and 1000-degrees-C). It is shown that the RuO2/Au thick-film system based on commercially available resistive and conductive inks allows continuous, long-term operation up to 400-degrees-C. Moreover, the allowable operating temperature is much higher for heaters made from conductive films; for example PtAu heaters can operate successfully up to 600-degrees-C whereas fritless platinum heaters are satisfactory in the whole range demanded by electrochemical sensors.