Low loss TiO₂ channel waveguides

TiO₂ is gaining interest as material for integrated photonics, due to its high refractive index, large transparency window and high non-linear refractive index. Its low phonon energy makes it attractive for the realization of active devices in the visible frequency range. In this work, we optimize different process steps of the fabrication of low loss TiO₂ channel waveguides. The TiO₂ layers are deposited by DC sputter deposition, using a mixed Ar/O₂ plasma. Removing the hysteresis in the deposition process, results in reduced propagation losses of the TiO₂ films (estimated less than 1.5 dB/cm at 632 nm wavelength). An E-beam lithography process is utilized to reduce the sidewall roughness of the waveguides. Different reactive gasses are compared to optimize the reactive ion etching recipe. BCl₃ in combination with HBr shows to be most beneficial for etching TiO₂ with high selectivity towards negative E-beam resist. A selectivity of 2.7 for TiO₂ over the E-beam resist is obtained. The performance of a TiO₂ a channel waveguide fabricated with the process before and after optimization is compared. The waveguide fabricated using the non-optimized process exhibited losses of 7.82±0.52 dB/cm at a wavelength of 632.8 nm, after applying an SiO₂ cladding. After process optimization, 5.08±0.65 dB/cm were obtained, without an SiO₂ cladding.