Tuning the Metal-Insulator Transition Properties of VO Thin Films with the Synergetic Combination of Oxygen Vacancies, Strain Engineering, and Tungsten Doping.

Vanadium oxide (VO) is considered a Peierls-Mott insulator with a metal-insulator transition (MIT) at T = 68° C. The tuning of MIT parameters is a crucial point to use VO within thermoelectric, electrochromic, or thermochromic applications. In this study, the effect of oxygen deficiencies, strain engineering, and metal tungsten doping are combined to tune the MIT with a low phase transition of 20 °C in the air without capsulation. Narrow hysteresis phase transition devices based on multilayer VO, WO, MoWO and/or MoO oxide thin films deposited through a high vacuum sputtering are investigated. The deposited films are structurally, chemically, electrically, and optically characterized. Different conductivity behaviour was observed, with the highest value towards VO/WO and the lowest VO on FTO glass. VO/WO showed a narrow hysteresis curve with a single-phase transition. Thanks to the role of oxygen vacancies, the MIT temperature decreased to 35 °C, while the lowest value (T = 20 °C) was reached with MoWO/VO/MoO structure. In this former sample, MoWO was used for the first time as an anti-reflective and anti-oxidative layer. The results showed that the MoO bottom layer is more suitable than WO to enhance the electrical properties of VO thin films. This work is applied to fast phase transition devices.