Influence of Conduction Mechanism Changes on the Sensor Performance of SMOX Based Gas Sensors

DC electrical resistance measurements on undoped polycrystalline SnO2 thick film sensing layers are performed to check if, under CO exposure in realistic application conditions (dry or humid air), a change in conduction mechanism is possible. The results show for CO concentrations below 250 ppm in dry air, that the conduction through the sensing layer is controlled by the surface depletion layer. Increasing the CO concentration in humid air, a change in conduction mechanism can be observed at CO concentrations below 15 ppm. In the present studies, the possibility and consequences of changes in the conduction mechanism for sensing with SnO2, as the most studied and used SMOX, are evaluated.