Effect of low-pressure postannealing on the electrical properties of VO2 thin films

Postannealing is an effective way to enhance the quality and performance of VO2 thin films. However, the presence of multiple chemical valence states of vanadium poses significant challenges for precise process control. In this work, low-pressure (10–50 Pa) postannealing, which can both reduce the excessive oxidation of the samples and avoid the generation of a large number of oxygen vacancies in the films, was employed to improve the crystalline quality as well as the electrical properties of VO2 films deposited on the SiO2/Si substrate by RF magnetron sputtering. As the annealing temperature rises, the as-deposited amorphous films transform into crystal VO2 and exhibit a pronounced metal-to-insulator transition. At an annealing temperature of 500 °C, VO2 thin films with good crystallinity and a resistance ratio ΔR (R30 °C/R85 °C) of more than 2 orders of magnitude before and after the phase transition were obtained; while at the annealing temperatures exceeding 550 °C, trace cluster structures (mainly composed of V6O13) were formed on the film surface as a result of overoxidation, leading to a degradation in electrical properties. Our study provides a practical, reasonable, and feasible method for the preparation of polycrystalline, high-quality VO2(M) films on SiO2/Si substrates.