Overcoming Si₃N₄ film stress limitations for high quality factor ring resonators

Silicon nitride (Si₃N₄) ring resonators are critical for a variety of photonic devices. However the intrinsically high film stress of silicon nitride has limited both the optical confinement and quality factor (Q) of ring resonators. We show that stress in Si₃N₄ films can be overcome by introducing mechanical trenches for isolating photonic devices from propagating cracks. We demonstrate a Si₃N₄ ring resonator with an intrinsic quality factor of 7 million, corresponding to a propagation loss of 4.2 dB/m. This is the highest quality factor reported to date for high confinement Si₃N₄ ring resonators in the 1,550 nm wavelength range.