Effect of Oxide Buffer Layer on the Thermochromic Properties of VO₂ Thin Films

VO₂ thin films were deposited on soda lime glass substrates with ZnO, TiO₂, SnO₂, and CeO₂ thin films applied as buffer layers between the VO₂ films and the substrates in order to investigate the effect of buffer layer on the formation and the thermochromic properties of VO₂ film. Buffer layers with thicknesses over 50 nm were found to affect the formation of VO₂ film, which was confirmed by XRD spectra. By using ZnO, TiO₂, and SnO₂ buffer layers, monoclinic VO₂ (VO₂(M)) film was successfully fabricated on soda lime glass at 370 °C. On the contrary, films of VO₂(B), which is known to have no phase transition near room temperature, were formed rather than VO₂(M) when the film was deposited on CeO₂ buffer layer at the same film deposition temperature. The excellent thermochromic properties of the films deposited on ZnO, TiO₂, and SnO₂ buffer layers were confirmed from the temperature dependence of electrical resistivity from room temperature to 80 °C. Especially, due to the tendency of ZnO thin film to grow with a high degree of preferred orientation on soda lime glass at low temperature, the VO₂ film deposited on ZnO buffer layer exhibits the best thermochromic properties compared to those on other buffer layer materials used in this study. These results suggest that deposition of VO₂ films on soda lime glass at low temperature with excellent thermochromic properties can be achieved by considering the buffer layer material having structural similarity with VO₂. Moreover, the degree of crystallization of buffer layer is also related with that of VO₂ film, and thus ZnO can be one of the most effective buffer layer materials.