High-yield, wafer-scale fabrication of ultralow-loss, dispersion-engineered silicon nitride photonic circuits

Low-loss photonic integrated circuits and microresonators have enabled a wide range of applications, such as narrow-linewidth lasers and chip-scale frequency combs. To translate these into a widespread technology, attaining ultralow optical losses with established foundry manufacturing is critical. Recent advances in integrated Si₃N₄ photonics have shown that ultralow-loss, dispersion-engineered microresonators with quality factors Q > 10 × 10⁶ can be attained at die-level throughput. Yet, current fabrication techniques do not have sufficiently high yield and performance for existing and emerging applications, such as integrated travelling-wave parametric amplifiers that require meter-long photonic circuits. Here we demonstrate a fabrication technology that meets all requirements on wafer-level yield, performance and length scale. Photonic microresonators with a mean Q factor exceeding 30 × 10⁶, corresponding to 1.0 dB m^-1 optical loss, are obtained over full 4-inch wafers, as determined from a statistical analysis of tens of thousands of optical resonances, and confirmed via cavity ringdown with 19 ns photon storage time. The process operates over large areas with high yield, enabling 1-meter-long spiral waveguides with 2.4 dB m^-1 loss in dies of only 5 × 5 mm² size. Using a response measurement self-calibrated via the Kerr nonlinearity, we reveal that the intrinsic absorption-limited Q factor of our Si₃N₄ microresonators can exceed 2 × 10⁸. This absorption loss is sufficiently low such that the Kerr nonlinearity dominates the microresonator's response even in the audio frequency band. Transferring this Si₃N₄ technology to commercial foundries can significantly improve the performance and capabilities of integrated photonics.