Wafer-size VO₂ film prepared by water-vapor oxidant

The growth of wafer-scale and uniform monoclinic VO₂ film with excellent phase transition property was a challenge if considering the multivalent nature of vanadium atom and the various phase structures of VO₂ compound. Direct oxidation of metallic vanadium film by annealing in oxygen gas or in air was suggested to be an easy way for VO₂ film preparation, while the oxidation parameters including the gas pressure, gas flux and annealing temperature were extremely sensitive due to the critical preparation window. Here we proposed a facile water-vapor assisted thermal oxidation to produce wafer-scale VO₂ films with good uniformity. Results indicated that by using the water vapor as the oxidizing agent, the temperature window for VO₂ growth was greatly broadened. In addition, the obtained wafer-size VO₂ film showed very uniform surface and sharp resistance change, which was attributed to the improved crystallinity and the high oxygen stoichiometry. The chemical reaction route was calculated based on Gibbs free energy, which confirmed the preferred growth of VO₂ film by wet oxidation. Our results not only demonstrated that the water vapor could be used as a modest oxidizing agent, but also showed the unique advantage for large size VO₂ film preparation, which was useful for practical devices applications in the future.