High quality vanadium dioxide films prepared by an inorganic sol-gel method

A novel preparation method we call the inorganic sol-gel method was developed to produce vanadium dioxide (VO2) thin films which exhibit an apparently reversible electrical resistance switching at about 60 °C. This method comprises the following processes: (1) V2O5 sols preparation by a quenching method, (2) V2O5 gel films preparation by dip-coating or spin-coating on glass substrates, and (3) the resulting films by vacuum heat-treatment. XRD analysis was used to study the existence of VO2 crystal in the films and ESCA was utilized to investigate the valence change in the films. The results showed that V(V) was reduced to lower valence vanadium. The abrupt electrical resistance change, up to 4–5 orders of magnitude at about 60 °C, which is a unique property of vanadium dioxide, was attributed to the existence of V(IV) in the films. The drop of the resistance of the films was larger than previously reported data, which is only 2–3 orders of magnitude when prepared on non-crystal substrates. It was also found that pretreatment of the gel films in water vapor at about 150 °C can lower the heat-treatment temperature for obtaining the desired films.