Transitional behavior of tin oxide semiconductor under a step-like humidity change

The effects of water vapor on SnO2, In2O3 and ZnO thick film sensors were investigated by measurement of resistances. Especially, the long span effects of water vapor were investigated on chemical kinetics in detail. Time-dependent behavior in resistance under a step-like change in humidity consisted of an initial large change followed by an exponential change in a long span, which was observed over a wide range of sensor temperature in the SnO2-based sensor. Such transitional behavior was also observed in the In2O3- and ZnO-based sensors. From a chemical kinetics-based analysis of the exponential change in SnO2, two different elementary reaction processes were assigned in each sensor temperature range above or below 330°C, respectively. It was found that the processes of adsorption and desorption of water vapor on semiconductor sensors were the time-consuming ones with an inherent activation energy in each sensor temperature range. Thus, some important findings to evaluate the effects of water vapor on the semiconductor sensors were obtained in the present study.