NEW MATERIALS CONSISTING OF MULTICOMPONENT OXIDES FOR THIN-FILM GAS SENSORS

High sensitivity for specific gas detection has been realized by new g as sensors incorporating multicomponent oxide thin films such as ZnO-I n2O3, MgO-In2O3, and Zn2In2O5-MgIn2O4 systems. The sensing properties of the multicomponent oxide thin-film sensors were strongly dependent on the composition of the films used. Sensors using ternary compounds such as Zn2In2O5 and MgIn2O4 always exhibited a higher sensitivity tha n those using binary compounds such as ZnO and In2O3. The sensors only exhibited an increase in resistance with exposure to carbon tetrachlo ride (CCl4) gas, whereas they exhibited a decrease in resistance for i nflammable gases such as butane (C4H10) and hexane (C6H14). The highes t sensitivity for CCl4 gas was obtained in a sensor using a Zn2In2O5-M gIn2O4 thin film prepared with a Zn2In2O5 content of about 60 mole per cent. The resistance of sensors operated at 300 degrees C was increase d by a factor of about 10(2) when exposed to CCl4 gas with a concentra tion of 350 ppm. The increase in resistance is attributed to the trapp ing of free electrons resulting from chlorine being adsorbed on grain boundaries and/or the film surface.