Radio frequency substrate biasing effects on the insulator-metal transition behavior of reactively sputtered VO2 films on sapphire (001)

Comprehensive studies have been performed on the effects of radio frequency (rf) substrate biasing on insulator–metal transition (IMT) properties of VO2 thin films grown on Al2O3 (001) substrates. As the rf substrate bias power increased, the ion energy during deposition increased, inducing a strong in-plane stress conversion and a modification of the rutile c-axis (cR-axis) length in the VO2 films. The reduced cR-axis length significantly lowered the IMT temperature. Increased IMT sharpness via improved crystallinity was obtained with rf substrate biasing at an appropriate power. Temperature coefficient of resistance at room temperature was comparable with reported values for impurity-doped VO2 films. Thus, the rf substrate biasing during reactive sputtering has great potential to control stress in thin films, which could finally control the IMT in oriented VO2 films.