Vanadium dioxide (VO2) is a strong-correlated metal-oxide with a sharp metal-insulator transition (MIT) for a range of applications. However, synthesizing epitaxial VO2 films with desired properties has been a challenge because of the difficulty in controlling the oxygen stoichiometry of VO x, where x can be in the range of 1 < x < 2.5 and V has multiple valence states. Herein, a unique moisture-assisted chemical solution approach has been developed to successfully manipulate the oxygen stoichiometry, to significantly broaden the growth window, and to significantly enhance the MIT performance of VO2 films. The obvious broadening of the growth window of stoichiometric VO2 thin films, from 4 to 36 °C, is ascribed to a self-adjusted process for oxygen partial pressure at different temperatures by introducing moisture. A resistance change as large as 4 orders of magnitude has been achieved in VO2 thin films with a sharp transition width of less than 1 °C. The much enhanced MIT properties can be attributed to the higher and more uniform oxygen stoichiometry. This technique is not only scientifically interesting but also technologically important for fabricating wafer-scaled VO2 films with uniform properties for practical device applications.
Keywords: epitaxy; metal−insulator transition; oxygen stoichiometry; vanadium dioxide films; wafer scale.