New multicomponent oxide materials for thin-film gas sensors

Cl-2 and O-3 gas detection at high sensitivity has been realized by newly developed thin-film gas sensors incorporating multicomponent oxides such as ZnO-In2O3, MgO-In2O3, and Zn2In2O5-MgIn2O4 systems. The sensors exhibited an increase in resistance with exposure to Cl-2 or O-3 gas. The sensing properties of the multicomponent oxide thin-film sensors were strongly dependent on the composition of the multicomponent oxide films used as well as the operating temperature. The highest sensitivity for Cl-2 and O-3 gases was obtained in sensors using a Zn2In2O5-MgIn2O4 thin film prepared with Zn2In2O5 contents of about 60 and 20mol.%, respectively: Cl-2 gas detected at a minimum concentration of 0.01 and O-3 gas at 0.4ppm. A fast response as well as a high sensitivity were obtained in these sensors operated with alternating exposures to air and Cl-2 or O-3 gas. The resistivity, carrier concentration and Hall mobility of the thin-film sensors were measured under operating conditions using the van der Pauw method. It should be noted that a decrease or increase of resistivity in the thin-film sensors resulted from a simultaneously increase or decrease of both carrier concentration and Hall mobility. The increase in resistivity is attributed to the trapping of free electrons resulting from Cl-2 and O-3 being adsorbed on grain boundaries and/or the film surface, the same as that produced by adsorption of oxygen. A Zn2In2O5-MgIn2O4 thin-film gas sensor exhibited very stable long term operation in an atmosphere with a high concentration of Cl-2 gas.