Coupled effects of deposition and annealing temperatures on optical, electrical and mechanical properties of titanium oxide thin films

• Thin films of titanium oxide were deposited with reactive DC magnetron sputtering.
• Mechanical and tribological properties increased with deposition temperature.
• Post-deposition annealing process had mixed effects on mechanical properties.
• Mechanical properties were controlled independently of optical and electrical.

In this study the influence of deposition temperature and a post-deposition annealing process on the optical, electrical, mechanical, and tribological properties of titanium oxide thin films was investigated. Based on high-resolution XPS, it was observed that the films became more metallic as the deposition temperature was raised from 15 to 450 °C. Moreover, the mechanical and tribological properties of the film deposited at 450 °C were at least 50% greater than for the film deposited at 15 °C. After annealing at 450 °C for 30 min in air, the films all became transparent and insulating. However, the annealing process had mixed effects on the mechanical and tribological properties such that the 15 and 250 °C films softened, but the 450 °C film hardened. This mixed trend is attributed to the different as-deposited film stoichiometries. The results show that the coupled effects of deposition temperature and post-deposition annealing are quite complex and that the mechanical properties of TiO2 thin films can be controlled independently of their optical and electrical properties. This is important because TiO2 coatings are often used as the outer-most layers in optical devices.