Sensing mechanism of SnO2 gas sensors

Studies of the gas sensing properties of both steady and unsteady state SnO2 thin film gas sensors in contact with CH4 and H2 in air from 400 to 500 C suggest a new sensing mechanism model for SnO2 semiconductor flammable gas sensors, based on: (i) sensor conductivity determined by the concentration of carrier electrons. (ii) Carrier concentration controlled by surface unsaturated oxygen adsorption site concentration which is decided by the balance between oxygen adsorption and the surface reaction between oxygen adsorbate and flammable gases. (iii) The activation energy of the reaction is changed by the Fermi energy change for any change in sensor conductivity. This model explains all experimental results. 14 refs.