The Electric Properties of VO2 Thin Films Doped with Other Metal Oxides under Water Vapor

Abstract

Abstract The electric property of a pure VO2 thin films, prepared from a vanadium naphthenate by thermal decomposition, was examined preliminarily under various inorganic gas atmospheres, H2O, H2, O2, N2O, and NO2, at 20–200 °C. Only in the case of the H2O adsorption, did the conductivity-temperature curve change reversibly; in the other cases it changed irreversibly. With respect to the VO2 films doped with Na2O, ZrO2, Cr2O3, and TiO2, similarly, the conductivities changed reversibly with the water vapor adsorbed; the extent and the manner of these changes differed rather greatly depending upon the kind of metal oxides doped. In the Zr–VO2 film, which had a large conductivity (σ) and its gap (Δσ) at the transition point (Tt=60 °C) relative to the pure VO2 film, the electric property was almost unaffected by water–vapor adsorption. In the cases of the Cr– and Ti–VO2 films, with quite small σ and Δσ values relative to the pure VO2 film, on the contrary, the In σ–1/T curves decreased parallelly to less than about one-half of that under a vacuum throughout the temperature range. With the Na–VO2 film, the σ–1/T curve measured under water vapor gradually nears that under a vaccum with the elevation of the temperature to 200 °C. From the comparisons of the effects of the electric properties of these doped films on the water vapor adsorbed, the structural features of the films, especially the contact states in the boundary layer, were deduced favorably. Furthermore, a possibility of the application to a switching element working at about 60 °C was suggested for the Zr–VO2 film, and that to a fume sensor working at a temperature less than 200 °C, for the Cr– and Ti–VO2 films.