Mechanism of gas detection in polycrystalline thick film SnO2 sensors

Abstract A quantitative model for the dependence of surface conductance on reducing gas concentration in polycrystalline SnO 2 films is developed. It is based on the assumptions that reducing gases react with oxygen chemisorbed on SnO 2 , inducing intergranular barrier height variations, and that the hole contribution to surface conductivity is important, especially at low gas concentrations, in spite of n-type bulk conduction. On applying this model to experimental data it was found that in air, at about 600 K, surface conductivity was intrinsic in our own gas sensors, but p type in Figaro TGS-100 sensors. In addition, as a result of prolonged heat treatment in pure oxygen, surface conductivity in our gas sensors clearly became p type, as shown by their behaviour as detectors in a chromatographic arrangement.