Microstructural, mechanical and optical properties of tungsten oxide coatings fabricated using superimposed HiPIMS-MF systems

Abstract

In this study, the under-stoichiometric WOx thin films were fabricated using a high power impulse magnetron sputtering (HiPIMS) and a superimposed HiPIMS-mid-frequency (MF) system. The oxygen flow rate ratios were varied from 33% to 83% while maintaining the same working pressure for all depositions at 0.4 Pa. The ratio of oxygen to tungsten, x value of WOx, increased from 2.07 to 2.40 as the oxygen flow rate ratio increased from 33% to 83%. For the WOx thin films deposited using oxygen flow rate ratios higher than 33%, the nanocrystalline monoclinic W25O73 phase was produced by a superimposed HiPIMS-MF or by a pure HiPIMS. As compared with the pure HiPIMS, the superimposed HiPIMS-MF technique fabricated WOx thin film with higher deposition rate and higher hardness. The WO2.28 film showed the highest hardness of 8.6 GPa. The highest optical bandgap value of 3.38 eV was achieved in WO2.29 film. The oxygen content, the O/W ratio, and the average transmittance of thin films increased with increasing O2 flow rate ratio.