Impact of sputtering parameters on titanium dioxide thin films for nonlinear nanophotonics

We have identified titanium dioxide (TiO2) as a promising material for on-chip nonlinear optical devices. Its high refractive index and large intrinsic nonlinearity can strongly enhance confinement and non-linear interactions. In this study we optimize our deposition process to lower the linear losses in planar waveguides. We deposit titanium oxide thin films by RF reactive sputtering titanium onto oxidized silicon wafers in an argon/oxygen environment. The oxygen partial pressure in the chamber has a large impact on the deposition rate and the film composition. We investigate the composition of our films by X-ray photoelectron spectroscopy. Titanium dioxide is known to exist in different crystalline phases of which we observe amorphous, anatase and rutile, identified using Raman spectroscopy. We will discuss the impact of the deposition parameters on the composition and phase of the films. We measure the refractive indices and planar waveguiding losses of our thin films by the prism coupling and spectroscopic ellipsometry methods. These films have refractive indices as high as 2.4 and losses as low as 0.4 dB/cm at a wavelength of 800 nm. We will discuss the influence of the phase and composition of the material on its optical properties and consequences for nonlinear nano-photonics.