Hybrid Scandium Aluminum Nitride/Silicon Nitride Photonic Integrated Circuits

Scandium-doped aluminum nitride has recently emerged as a promising material for quantum photonic integrated circuits (PICs) due to its unique combination of strong second-order nonlinearity, ferroelectricity, piezoelectricity, and complementary metal–oxide–semiconductor (CMOS) compatibility. However, the relatively high optical loss reported to date─typically above 2.4 dB/cm─remains a key challenge that limits its widespread application in low-loss PICs. Here, we present a monolithically integrated Si 3 N 4 –ScAlN waveguide platform that overcomes this limitation. By confining light within an etched Si 3 N 4 waveguide while preserving the functional properties of the underlying ScAlN layer, we achieve an intrinsic quality factor of Q i = 3.35 × 10 5, corresponding to a propagation loss of 1.03 dB/cm─comparable to that of commercial single-mode silicon-on-insulator (SOI) waveguides. This hybrid architecture enables low-loss and scalable fabrication while retaining the advanced functionalities offered by ScAlN, such as ferroelectricity and piezoelectricity. Our results establish a new pathway for ScAlN-based PICs with potential applications in high-speed optical communication, modulation, sensing, nonlinear optics, and quantum optics within CMOS-compatible platforms.