A micromachined gas sensor based on a catalytic thick film/SnO2 thin film bilayer and thin film heater

A micromachined gas sensor based on a catalytic thick film/SnO2 thin film bilayer and a thin film heater was investigated for CH4 sensing. The sensor demonstrated good sensitivity and high selectivity with low power consumption. The thin film heater and the SnO2 thin film sensing layer were deposited on a Si micromachined structure having a silicon oxide-silicon nitride membrane. On the SnO2 sensing layer, a Pd-Al2O3 catalytic thick film was formed to oxidize interfering gases selectively. The sensor realized low power consumption and fast thermal response due to the low thermal conductance and the small heat capacity of the membrane. The power consumption at an operating temperature of approximately 450DDGC was 30mW. The sensitivity (Rair/Rgas) to 2000ppm CH4 in air was greater than 5, while the sensitivity to H2, an interfering gas, was relatively low.