High-Q inverted silica microtoroid resonators monolithically integrated into a silicon photonics platform.

We report on the monolithic integration of a new class of reflown silica microtoroid resonators with silicon nanowaveguides fabricated on top of the silica film. Connectivity with other silicon photonics devices is enabled by inversion of the toroid geometry, defined by etching a circular opening rather than a disk in an undercut silica membrane. Intrinsic quality factors of up to 2 million are achieved and several avenues of process improvement are identified that can help attain the higher quality factors (> 10) that are possible in reflown microtoroids.