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

Abstract WO 3 thin films have been deposited on alumina substrates at different O 2 /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 WO 3 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 WO 3 thin film on the NO gas sensing performance is presented. It was found that the fabricated device using sub-stoichiometric WO 3−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 °C, with a fast response time (∼19 s) and recovery time (∼17 s). The NO gas sensing of WO 3 thin films has been tested at different operating temperatures (175–350 °C) and gas concentrations (1–50 ppm), witnessing a variation in sensor response. The NO gas sensing mechanism on the surface of WO 3 has also been discussed.