Integrated solid-state gas sensors based on SnO2(Pd) for CO detection

Thin films of polycrystalline Pd-doped tin dioxide SnO2(Pd), widely used as sensitive element in gas sensors devices for atmospheric pollutant as CO, have been deposited on Si substrates through the ultrasonic aerosol pyrolysis technique. It is firstly shown that the sensitivity S = (G - G(o))/G(o) to CO at low temperature (80-120 degrees C), measured on steady state regime by conductance-temperature characteristics, depends on the concentration x of Pd incorporated into the film and on the SnO2 grain size D. The highest sensitivity S corresponds to a very sharp (x, D) domain. Secondly, the films synthesised under these optimal conditions have been integrated to a silicon-based prototype of micro-sensor. This device provides stable response in dynamic regime (S = 17) at low temperature (similar to 100 degrees C) to 50 ppm CO by using a short-term annealing (T-annealing = 350 degrees C, t(annealing) = 5 min) before each measurement. (C) 1999 Elsevier Science S.A. All rights reserved.