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

The non-ohmic conductance behaviour of some SnO2-based thick-film sens ors has been studied both by a computer simulation and by practical ex periments. Current-voltage characteristics have been measured in the v oltage range 0-20 V at different temperatures. In the computer simulat ion, a three-dimensional random barrier network is used to describe po lycrystalline SnO2 thick films. The basic unit in the network is a com ponent describing the surface Schottky barrier at intergrain contacts and obeying non-ohmic behaviour. I-U characteristics have been calcula ted 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-linea rity at low temperatures, but this behaviour decreases with increasing temperature. Some comparisons between calculated results and those fr om analytical expressions are also given in the ohmic range at low vol tages.