Low-noise microwave oscillators using integrated lasers and ultra-high-Q microresonators

Abstract

A key ingredient here is the ultra-high-Q silicon nitride (SiN) ring resonators fabricated at a CMOS foundry [1]. The silicon nitride waveguide has a high aspect-ratio SiN core (100 nm thick) surrounded by buried 14.5-um thick thermal oxide cladding and top deposited upper cladding of 2-um thickness. Over 20 h of annealing at 1,150 °C is employed to minimize the residual hydrogen content of the deposited SiN and SiO2 films. The fabricated silicon nitride ring resonators reported here have different FSRs of 5.4 GHz, 10.8 GHz and 30 GHz. Statistic measurement of the entire 200-mm-diameter wafer unveils that wafer-scale high-yield ultralow loss waveguides are achieved. The nominal intrinsic Q factors are over 200 million for 30 GHz ring resonators (with finesse over 42,000), and around 100 million for 5 GHz ring resonators that employ a narrower SiN waveguide core.