Ultralow-loss photonic integrated chips on 8-inch anomalous-dispersion Si${}_3$N${}_4$-SiO${}_2$-Si Wafer

We report the fabrication of 8-inch crack-free, dispersion-engineered Si${}_3$N${}_4$-SiO${}_2$-Si wafers fully compatible with industrial foundry silicon photonics fabrication lines. By combining these wafers with a developed amorphous silicon (a-Si) hardmask etching technique, we achieve ultra-low-loss Si${}_3$N${}_4$ photonic integrated circuits (PICs) with intrinsic quality factors exceeding $25\times {10}^6$ using electron beam lithography and $24\times {10}^6$ using standard ultraviolet stepper photolithography. Frequency-comb generation is demonstrated on these high-quality Si${}_3$N${}_4$ PICs, corroborating the designed anomalous dispersion. These results establish the feasibility of mass-manufacturing high-performance, dispersion-engineered Si${}_3$N${}_4$ PICs using standard foundry-grade processes, opening new pathways for applications in optical communications, nonlinear optics, and quantum optics.