Integrated Si₃N₄ microresonator-based quantum light sources with high brightness using a subtractive wafer-scale platform

The silicon nitride (Si₃N₄) platform, demonstrating a moderate third-order optical nonlinearity and a low optical loss compared with those of silicon, is suitable for integrated quantum photonic circuits. However, it is challenging to develop a crack-free, wafer-scale, thick Si₃N₄ platform in a single deposition run using a subtractive complementary metal-oxide-semiconductor (CMOS)-compatible fabrication process suitable for dispersion-engineered quantum light sources. In this paper, we demonstrate our unique subtractive fabrication process by introducing a stress-release pattern prior to the single Si₃N₄ film deposition. Our Si₃N₄ platform enables 950 nm-thick and 8 μm-wide microring resonators supporting whispering-gallery modes for quantum light sources at 1550 nm wavelengths. We report a high photon-pair generation rate of ∼1.03 MHz/mW², with a high spectral brightness of ∼5×10⁶ pairs/s/mW²/GHz. We demonstrate the first heralded single-photon measurement on the Si₃N₄ platform, which exhibits a high quality of conditional self-correlation gH⁽²⁾(0) of 0.008 ± 0.003.