HiPIMS-deposited thermochromic VO2 films with high environmental stability

- HiPIMS and RFMS deposition of thermochromic VO2.
- Good durability of HiPIMS deposited VO2 in humid conditions.
- SiNx demonstrate oxidation-protection of RFMS and HiPIMS coatings.

A comparative study of the environmental stability of high power impulse magnetron sputtered (HiPIMS) and radio frequency magnetron sputtered (RFMS) thermochromic vanadium dioxide thin films in a highly oxidizing environment has been performed. We observe that RFMS-deposited VO2 films quickly transform into V2O5 at 80 °C and 100% relative humidity while HiPIMS-deposited films retain their thermochromic behaviour at least three times longer. Following a thorough analysis of the films, this increase in performance is ascribed to the films' higher density and larger average grain size. The results indicate that the HiPIMS process provides sufficient durability for VO2 films without the need for a diffusion barrier used in typical everyday conditions. Still, when a 35 nm thick SiNx diffusion barrier is added on top of the HiPIMS VO2 films, the thermochromic device shows less than 5% loss in thermochromic performance following extended accelerated ageing.