Fabricating highly stable and reliable vanadium dioxide thin films: Insights from radio frequency magnetron sputtering

This study establishes an optimization protocol to fabricate a stoichiometric VO<inf>2</inf> thin film onto the glass substrate using a single process step in RF magnetron sputtering. An interplay between the substrate temperature and the oxygen-to-argon ratio in process gas is shown to achieve a range of VO<inf>x</inf> composition (from oxygen-rich to oxygen-deficient phases). The re-sputtering phenomenon is found to be crucial at higher temperature (T ≥ 873 K), leading to a shift in stoichiometry from V<inf>2</inf>O<inf>5</inf> to V<inf>2</inf>O<inf>3</inf>. Moreover, a process model for the fabrication of various VO<inf>x</inf> compounds in thin film form is also established in this study. The crystal structure transformation from M<inf>1</inf> to R phase for these VO<inf>2</inf> thin films deposited over a range of process conditions is found to be 339 ± 1 K, in close agreement with the reported value for the bulk VO<inf>2</inf>. In spite of the microstructural variations, these films are found to show consistent phase transition behavior, excellent stability, and reliability in repeated thermal cycles. These films show a semiconductor-to-metal transition, which is correlated to their structural phase transformation temperature. Moreover, this study also establishes a correlation between various external stimuli, widening the usage of this material in a range of applications.