Investigation of TiO2 based thin films deposited by reactive magnetron sputtering for use at high temperatures

The temperature stability of different TiO2 thin films with high refractive index is investigated. The films were deposited by reactive pulsed magnetron sputtering in a double magnetron set up using two Al and Ti metallic targets. For pure TiO2 films, temperature stability of up to 800°C could be demonstrated. For further improvement of the temperature stability, different TiAlOx mixed oxide films were deposited. We found out that for a specific mixture, films with a high refractive index can be deposited which are stable and optically clear for temperatures up to 900°C. Due to the inclusion of Al cations into the TiO2 matrix, the TiAlOx films show a high rutile fraction and maximum refractive index of 2,5 at 550 nm in the as grown state. The AlTiOx films were identified to be clearly superior to the 'simple' TiO2 films. This is explained by the suppression of the thermally induced growth of the anatase phase and therefore, the suppression of the phase transition of anatase rutile.