THIN-FILM GAS CATALYTIC MICROSENSOR

This paper describes a catalytic calorimetric gas sensor which is fabricated by means of thin-film techniques. A glass substrate is covered with a thin layer of catalytic metal, such as platinum (2-10-mu-m). The active area of the catalyst is a meandered filament, about 180-mu-m wide and 1.8 mm long. The substrate under this active area is etched away in order to obtain a free-standing microfilament, so that a minimum amount of heat is lost by thermal conduction. With this structure the catalyst can be heated to a high temperature (800-1000-degrees-C) with a low electrical power (almost-equal-to 100-250 mW). The device generally works in a pulsed mode. An electrical pulse of less than 50 ms is long enough to measure the filament resistance at working temperature. For methane detection, the sensor sensitivity is about 17 mV/V for 1% of flammable gas in air at 800-degrees-C.