A Comparative Study of Gas Sensing Properties of Tungsten Oxide, Tin Oxide and Tin-Doped Tungsten Oxide Thin Films for Acetone Gas Detection

Nowadays, various metal oxide thin films have been used for the purpose of gas sensing. This research depicts a comparison of gas sensing properties among four different metal oxide thin films, namely, tungsten dioxide (WO2), tungsten trioxide (WO3), tin oxide (SnO2) and tin doped tungsten trioxide (Sn-doped WO3), for detecting acetone gas. Each metal oxide thin film was subjected tp acetone gas flow of various concentrations and the corresponding changes in resistance were calculated. Characterizations such as x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and gas sensing characterization for recording resistance changes have been performed. Each film was annealed at different temperatures for 1 h (WO2 and WO3 at 500 degrees C, SnO2 at 300 degrees C and Sn-doped WO3 at 400 degrees C) so as to achieve an optimum grain size for sensing. The XRD patterns reveal formation of an orthorhombic phase of WO2, hexagonal phase of WO3 and orthorhombic phase of SnO2. AFM and SEM depict clear images of grain boundaries on the film. SnO2 has been found to be the best thin film for sensing acetone gas. Operational optimum temperature for sensing acetone gas has been calculated for each thin film (260 degrees C for WO2, 220 degrees C for WO3, 360 degrees C for SnO2 and 300 degrees C for Sn-doped WO3). It can detect a very low concentration of 1.5ppm acetone gas with a good resistance response change of 30%. Various concentrations of acetone gas, namely, 1.5ppm, 3ppm, 5ppm, 7ppm, 10ppm, 15ppm and 20ppm, have been detected using these metal oxide thin films, and thus the comparison has been made. The response time for SnO2 is approximately 3min and recovery time is approximately 4min.