Tuning the Metal–Insulator Transition Properties of VO2 Thin Films with the Synergetic Combination of Oxygen Vacancies, Strain Engineering, and Tungsten Doping

Vanadium oxide (VO2) is considered a Peierls–Mott insulator with a metal–insulator transition (MIT) at Tc = 68° C. The tuning of MIT parameters is a crucial point to use VO2 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 VO2, WO3, Mo0.2W0.8O3, and/or MoO3 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 VO1.75/WO2.94 and the lowest VO1.75 on FTO glass. VO1.75/WO2.94 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 (Tc = 20 °C) was reached with Mo0.2W0.8O3/VO2/MoO3 structure. In this former sample, Mo0.2W0.8O3 was used for the first time as an anti-reflective and anti-oxidative layer. The results showed that the MoO3 bottom layer is more suitable than WO3 to enhance the electrical properties of VO2 thin films. This work is applied to fast phase transition devices.