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 was 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 a temperature stability of up to 800 °C was demonstrated. For further improvement of the temperature stability, different TiAlOx mixed oxide films were deposited. It was found that for a mixture region 0.75 < (Ti / Ti + Al) < 0.90 films 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, these TiAlOx films show a high rutile fraction and a maximum refractive index of 2.5 at 550 nm in the as-grown state. The temperature stability of the TiAlOx films was identified to be clearly superior to the pure TiO2 films. This is explained by the suppression of the thermally induced growth of the anatase phase and the resulting suppression of the phase transition from anatase to rutile.