Deposition of vanadium oxide films by direct-current magnetron reactive sputtering

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Abstract
Vanadium dioxide is well known for the semiconductor–metal phase transition at 67 °C which has yielded resistivity changes as high as 105 in single crystals. Our objective is to demonstrate that thin films with high transition resistivity ratios can be deposited at modest substrate temperatures by dc reative sputtering from a vanadium target in an O2–Ar working gas using a planar magnetron source, because of the capabilities of this method for depositing large-area thermal control surfaces. We have obtained resistivity ratios of ∼5×103, between a semiconductor phase with a resistivity of ∼5 Ω cm, and a metallic phase with a resistivity of ∼10−3 Ω cm for films deposited onto borosilicate glass substrates at ∼400 °C. X-ray diffraction showed the films to be single-phase VO2 with a monoclinic structure. The VO2 films are obtained for a narrow range of O2 injection rates which correspond to conditions where cathode poisoning is just starting to occur, i.e., where the sputtered flux of vanadium, as measured by in situ optical emission spectroscopy, is decreasing and the oxygen partial pressure is increasing. Higher or lower injection rates, for a given discharge current, give films with unfavorable stoichiometry and/or structure and lower resistivity ratios during the transition.

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