Ion-flux characteristics during low-temperature (300 °C) deposition of thermochromic VO2 films using controlled reactive HiPIMS

Abstract

The ion-flux characteristics at a substrate position and the corresponding discharge characteristics were investigated during controlled low-temperature (300 °C) reactive high-power impulse magnetron sputtering (HiPIMS) depositions of thermochromic VO2 films onto conventional soda-lime glass substrates without any substrate bias voltage and without any interlayer. It was shown that the phase composition of the films correlates with the (V+ + V2+) ion fraction and the (V+ + V2+):() ion ratio in the total ion flux onto the substrate. Setting the amount of oxygen in the gas mixture allowed us to control not only the phase composition of the films but also their crystallinity. It was found that an appropriate composition of the total ion flux and high ion energies (up to 50 eV relative to ground potential) support the crystallization of the thermochromic phase in the VO2 films. We achieved a high modulation of the transmittance at 2500 nm (between 51% and 8%) and of the electrical resistivity (changed 350 times) for a 88 nm thick VO2 film.