Structural and Electrical Properties of Vanadium Dioxide Thin Films

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Abstract
Reactively sputtered vanadium dioxide films have been analyzed to determine the relation between their electrical and structural properties. The structure of the thin films was determined by x-ray diffraction, reflection electron diffraction, and electron microscopy of carbon replicas of the film surfaces. The various substrates which were evaluated for thin film VO2 deposition were amorphous glass, glazed ceramic, and single-crystal sapphire and rutile. Electrical conductivity measurements were made to correlate film perfection with the conductivity ratio between the semiconducting and metallic states. Films deposited on amorphous substrates such as glass and glazed ceramic are polycrystalline in structure with small grain size. Conductivity ratios of approximately 102 were observed with a very broad transition region centered at 68 °C. These films, in addition to VO2, exhibit an extra x-ray line at d = 2.25, tentatively identified as VO1.87. On sapphire substrates, highly textured films were obtained while the films deposited on rutile substrates were epitaxial. In both cases conductivity ratios of 3.5 × 103 were observed. While the epitaxial films had better structural perfection, the conductivity ratio was no better than the textured films. A large grain size is considered to be the dominant factor in achieving high conductivity ratios in these VO2 films.

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