Thermochromic VO2 Films Heteroepitaxially Grown on ZnO Coated Glass by RF Sputtering

ABSTRACTVanadium dioxide (VO2) is one of the most attractive thermochromic materials, which shows large changes in optical and electrical properties at around 68°C, nearly room temperature. This thermochromic behavior has been explained in terms of the Mott-Hubbard transition from a high-temperature rutile structure (metal phase) to a low-temperature monoclinic structure (semiconductor phase). We already reported that rf magnetron sputtering using V2O3 or V2O5 targets enable us to deposit polycrystalline thermochromic VO2 films with high reproducibility by introduction of oxygen gas (O2/(Ar+O2)=1∼1.5%) or hydrogen gas (H2/(Ar+H2)=2.5∼10%), respectively, as reactive gases [see ref.1]. In this study, ZnO polycrystalline films were deposited as a buffer layer between the VO2 film and glass substrate also by rf magnetron sputtering, which have been known to exhibit <001> preferred orientation in the wide range of the deposition conditions. Very thin thermochromic VO2 films with thickness of 50nm were successfully deposited on the ZnO coated glass substrate because of the heteroepitaxial relationship of VO2(010)[100]//ZnO(001)[100],[010],[110].