CMOS compatible monolithic multi-layer Si_3N_4-on-SOI platform for low-loss high performance silicon photonics dense integration

We demonstrated a low-loss CMOS-compatible multi-layer platform using monolithic back-end-of-line (BEOL) integration. 0.8dB/cm propagation loss is measured for the PECVD Si₃N₄ waveguide at 1580nm wavelength. The loss is further reduced to 0.24dB/cm at 1270nm wavelength, justifying the platform's feasibility for O-band operation. An inter-layer transition coupler is designed, achieving less than 0.2dB/transition loss across 70nm bandwidth. This is the lowest inter-layer transition loss ever reported. A thermally tuned micro-ring filter is also integrated on the platform, with performance comparable to similar device on SOI platform.