SIMULATION STUDIES OF NONOHMIC CONDUCTANCE BEHAVIOR IN SNO2 THICK-FILM GAS SENSORS

The non-ohmic conductance behaviour of some SnO2-based thick-film sensors has been studied both by a computer simulation and by practical experiments. Current-voltage characteristics have been measured in the voltage range 0-20 V at different temperatures. In the computer simulation, a three-dimensional random barrier network is used to describe polycrystalline SnO2 thick films. The basic unit in the network is a component describing the surface Schottky barrier at intergrain contacts and obeying non-ohmic behaviour. I-U characteristics have been calculated at different temperatures for networks with different coordination and with different distributions of barrier heights. Results both of the simulation calculations and of experiments show a strong non-linearity at low temperatures, but this behaviour decreases with increasing temperature. Some comparisons between calculated results and those from analytical expressions are also given in the ohmic range at low voltages.