Effects of annealing on optical properties of TiO2 planar waveguides

Titanium dioxide possesses a high second order nonlinear index, making it a potential material for all-optical switching. In order to exploit these properties, TiO2 thin films with high refractive indices and low losses are required. We deposit TiO2 waveguides via RF reactive sputtering onto oxidized silicon substrates. We find that film characteristics vary greatly with deposition temperature, suggesting that they may also exhibit strong sensitivity to post-deposition annealing. We annealed TiO2 thin films at various temperatures in an oxygen environment using a tube furnace. The annealed films are then characterized using Raman spectroscopy, variable angle scanning ellipsometry and prism coupling to observe changes in crystalline phase, refractive index, and planar waveguide losses, respectively. As-deposited amorphous films demonstrate an increase in crystallinity after annealing, with the development of the anatase, and, at higher temperatures, rutile crystalline phases. We report on the changes in refractive index and planar waveguide loss that accompany these phase changes, and their consequences for the viability of TiO2 as a device medium. Furthermore, we will study the changes in the nonlinear properties of these films upon annealing using the Z-scan technique.