Effect of the thickness of reactively sputtered WO3 submicron thin films used for NO2 detection

Abstract

Abstract Tungsten trioxide (WO 3 ) thin films were prepared by magnetron sputtering onto silicon micro-machined substrates. The dependence of the thin film thickness (varied from 37.5 to 400 nm) on NO 2 gas sensing properties was investigated. The structure, grain size and chemical composition of the deposited WO 3 films have been studied by X-ray diffraction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS), respectively. Our results show that the films are formed by grains crystallized in the WO 3 monoclinic phase with preferential orientations along the c axis. The grain size increased with the film thickness. The gas sensing characteristics of the sensors such as sensitivity (normalized response), response time, recovery time and aging were investigated for NO 2 detection and related to the film thickness. For example, a maximum response of 200 was obtained for 37.5 nm thick films operated at 350 °C.