Optical and electrical switching properties of VO₂ thin film on MgF₂ (111) substrate

High-quality VO₂ thin films were epitaxially deposited on MgF₂ (111) single crystal substrate by means of magnetron sputtering process. The epitaxial relation of VO₂ film and MgF₂ (111) substrate was denoted as (210)VO₂(M)//(111) MgF₂ or (111) VO₂(R)//(111) MgF₂, which was determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The optical contrast between the semiconductor phase and metallic phase in the infrared region exceeds 40%, which holds great potential applications in optical switching. The energy-saving effect of VO₂ films as the intelligent coating of smart window, which is commonly supposed to be one of the typical employments of optical switching performance, can be optimized by regulating the grain size of VO₂ films. The resistance-temperature curves were measured by a specially customized resistance testing platform and corresponding thermochromic parameters, such as transition temperature, SMT width, activation energy, et al., were evaluated. The largest resistance ratio between the two phases exceeds 5 orders of magnitude, which can function as excellent electrical switching and may find its applications in a variety of novel switching devices.