Evolution of structure and electrical properties with annealing time in solution-based VO2 thin films

Abstract

Vanadium dioxide (VO2) thin films were prepared on c-sapphire substrates by using an easy sol–gel method and sequential vacuum annealing process. The effects of annealing time on the structure, morphology and phase transition properties were investigated. The results show that, with the extended annealing time from 1h to 7h, the films have transformed from V2O3 to V3O5, and then VO2. The VO2 thin films prepared with the annealing time of 4h or 7h display good phase transition property with the resistance change up to 3 orders of magnitude. Furthermore, the 7h-sintered film has better growth orient, bigger grain size and lower phase transition temperature comparing with the 4h-sintered film. It is suggested that, the prolonged annealing treatment will be in favor of the crystal film quality and enhance the related phase transition property for the solution-based VO2 films. Based on the Raman results, we have discussed the possible reactions and evolution mechanisms during the VO2 film preparation with different annealing time.