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

Abstract

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 Si ₃N ₄ photonics have shown that ultralow-loss, dispersion-engineered microresonators with quality factors Q > 10 × 10 ⁶ 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 × 10 ⁶, 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 mm ² size. Using a response measurement self-calibrated via the Kerr nonlinearity, we reveal that the intrinsic absorption-limited Q factor of our Si ₃N ₄ microresonators can exceed 2 × 10 ⁸. This absorption loss is sufficiently low such that the Kerr nonlinearity dominates the microresonator’s response even in the audio frequency band. Transferring this Si ₃N ₄ technology to commercial foundries can significantly improve the performance and capabilities of integrated photonics.

Abstract

For widespread technological application of nonlinear photonic integrated circuits, ultralow optical losses and high fabrication throughput are required. Here, the authors present a CMOS fabrication technique that realizes integrate photonic microresonators on waver-level with mean quality factors exceeding 30 million and 1 dB/m optical losses.