HIGH-QUALITY VANADIUM DIOXIDE FILMS PREPARED BY AN INORGANIC SOL-GEL METHOD

A novel preparation method we call the inorganic sol-gel method was de veloped to produce vanadium dioxide (VO2) thin films which exhibit an apparently reversible electrical resistance switching at about 60 degr ees C. This method comprises the following processes: (1) V2O5 sols pr eparation by a quenching method, (2) V2O5 gel films preparation by dip -coating or spin-coating on glass substrates, and (3) the resulting fi lms by vacuum heat-treatment. XRD analysis was used to study the exist ence 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 redu ced to lower valence vanadium. The abrupt electrical resistance change , up to 4-5 orders of magnitude at about 60 degrees C, which is a uniq ue 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 t han previously reported data, which is only 2-3 orders of magnitude wh en prepared on non-crystal substrates. It was also found that pretreat ment of the gel films in water vapor at about 150 degrees C can lower the heat-treatment temperature for obtaining the desired films.