Microstructure and properties of VO2 thin films deposited by MOCVD from vanadyl acetylacetonate

Abstract

Thin films of vanadium dioxide have been deposited on glass by low pressure metal-organic chemical vapour deposition using the β-diketonate complex, vanadyl acetylacetonate, as the precursor. It is found that nearly monophasic, monoclinic VO2(M) films are formed in the narrow temperature range 475–520 °C, films formed outside this range comprising significant proportions of other vanadium oxide phases beside VO2(M). The microstructure of these well-crystallized films varies significantly with temperature in this range. Films grown at 475 °C are dense and have a very strong (200) orientation. At 520 °C, films are somewhat porous, and display little preferred orientation. Film microstructure influences the semiconductor–metal transition noticeably. Films deposited at 475 °C have a large change in resistance at 66 °C, and display a small temperature hysteresis in the transition. The transition temperature in films grown at 520 °C is higher (72 °C), whereas the change in resistance is smaller and the hysteresis larger. An attempt has been made to understand the unusual microstructure of VO2 films grown on glass substrates. The variation in the phase transition characteristics is interpreted in terms of the observed film microstructure. The thermal properties of the CVD precursor are also reported.