Sensing mechanism of SnO2 gas sensors

Studies have been made 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. The results suggest a new sensing mechanism model for SnO₂ semiconductor flammable gas sensors. This model is based on the following points: (i) Sensor conductivity is determined by the concentration of carrier electrons. (ii) Carrier concentration is 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.