Analysis of the sensing mechanism of tin dioxide thin film gas sensors using the change of work function in flammable gas atmosphere

Abstract

To investigate the sensing mechanism of SnO 2 thin films prepared with the targets-facing type sputtering method, the change of work function of the films was measured with the Kelvin method, and was compared with the change of resistance when they were exposed to hydrogen. The change of work function in the same concentration of hydrogen shows different trends according to the variation of the film temperature and this result reveals that there exist three different models of hydrogen interaction with the film surface or with the oxygen adsorbates on the surface, which depend on the film temperature at that time. The change of resistance of the films shows quick saturation, while that of the work function has trends of slow and continuous decreasing; from these results, it is concluded that the adsorption or desorption of the oxidizing or reducing gases on the film surface are contributed mainly to the change of potential barrier of grain boundaries of the films.