Tunable Metal-Insulator Properties of Vanadium Oxide Thin Films Fabricated by Rapid Thermal Annealing

Abstract

Vanadium oxide (VOx) thin films were fabricated by sputtering vanadium thin films on c-sapphire substrate followed by rapid thermal annealing in pure oxygen atmosphere. The surface morphology, crystal structure, electrical characteristics and near-infrared transmittance of the VOx films were studied by atomic force microscope (AFM), X-ray diffraction (XRD), four-point probe method and FT-IR/NIR Spectrometer, respectively. The insulator-metal phase transition temperature could be easily tuned from 57 to 49°C during heating and from 48 to 42°C during cooling by controlling the annealing time of rapid thermal annealing. This modulation effect of phase transition temperature is explained by carrier concentration originating from the different annealing times. The films with higher carrier concentration and smaller VO2 grain size tend to have lowered phase transition temperature. Besides, the widths of the hysteresis loops can also be regulated by controlling the annealing time. In addition, we find that films with coarser crystal sizes generally have a narrower hysteresis width. These results confirmed experimentally that carrier concentration, grain size and morphology of VOx films have significant effects on the properties of the metal-insulator transition; and rapid thermal process is a simple and effective way to tune phase transition properties of vanadium oxide thin films.