Role of oxygen vacancies in improving the NO gas sensing behavior of DC magnetron sputtered sub-stoichiometric WO3 thin films

Abstract WO3 thin films have been deposited on alumina substrates at different O2/Ar gas ratios and thicknesses by reactive DC magnetron sputtering for NO gas sensing. X-ray photoelectron spectroscopy (XPS) confirms the presence of oxygen vacancies in all monoclinic-phase WO3 thin films. A systematic decrease in the band gap was found with an increase in the oxygen vacancies leading to a significant upward shift in the Fermi level. Here, the influence of stoichiometry of WO3 thin film on the NO gas sensing performance is presented. It was found that the fabricated device using sub-stoichiometric WO3-x showed enhanced performance in terms of high stability, high selectivity, and fast response/recovery time with a sensor response of 147 for 50 ppm NO concentration at 275 oC, with a fast response time (~ 19 s) and recovery time (~ 17 s). The NO gas sensing of WO3 thin films has been tested at different operating temperatures (175–350 oC) and gas concentrations (1–50 ppm), witnessing a variation in sensor response. The NO gas sensing mechanism on the surface of WO3 has also been discussed.