Temperature effects on structure and optical properties of radio-frequency sputtered VO2

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Abstract
Vanadium dioxide undergoes a first-order phase transformation near 67 °C. This phase transformation is accompanied by significant changes in optical properties. The most pronounced changes occur between IR wavelengths of 2 and 12 μm; therefore, thin films of this material appear very attractive for uses in IR optical switching devices. By knowing the effects that deposition temperature has on the optical properties and relating these properties to the film microstructure, a process for fabricating films with optimal properties and desired microstructure can be developed. Vanadium oxide films were deposited on sapphire substrates by rf magnetron sputtering. At deposition temperatures of 350 °C, polycrystalline films were observed. X-ray diffraction analysis indicated VO2 and V4O7 to be the phases present, and optical characterization showed a contrast in transmission of <20% between the switched and unswitched states. As the deposition temperature was increased, dendritic growth was observed. Film composition was VO2 and V6O11 when the deposition temperature was 500 °C with improved optical properties at higher deposition temperatures. The changes in optical properties, microstructure, and composition shows the dependence that vanadium oxide has on the deposition temperature.

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