TiO₂ microring resonators with high Q and compact footprint fabricated by a bottom-up method

Abstract

Titanium dioxide (<i>T</i><i>i</i><i>O</i>₂) microring resonators (MRRs) with high quality factors (Qs) are demonstrated by using a new, to the best of our knowledge, bottom-up fabrication method. Pattern platforms with a T-shaped cross section are first defined by etching a thin top layer of silicon nitride and a thick bottom layer of silica and partially undercutting the silica. Then, <i>T</i><i>i</i><i>O</i>₂ is deposited on the platforms to form the <i>T</i><i>i</i><i>O</i>₂ waveguides and devices. <i>T</i><i>i</i><i>O</i>₂ MRRs with different bending radii, waveguide widths, and gaps in the bus waveguide are fabricated and measured. The intrinsic <i>Q</i>(<i>Q</i>_{<i>i</i><i>n</i><i>t</i>}) is achieved to be ∼1.1×10⁵ at the telecommunication wavelengths, corresponding to a bend waveguide loss of 3.9 dB/cm while the compact MRR with a radius of 10 µm can still sustain a <i>Q</i>_{<i>i</i><i>n</i><i>t</i>} of ∼10⁵. These results not only unfold the feasibilities of the proposed bottom-up method for fabricating <i>T</i><i>i</i><i>O</i>₂ waveguides and MRRs with high Qs and compact footprints but also suggest a new approach for fabricating waveguides in other materials, of which direct etching is not easily accessible.