Wafer-scale heterogeneous integration of thin film lithium niobate on silicon-nitride photonic integrated circuits with low loss bonding interfaces

Abstract

Silicon nitride (Si₃N₄) is a versatile waveguide material platform for CMOS foundry-based photonic integrated circuits (PICs) with low loss and high-power handling. The range of applications enabled by this platform is significantly expanded with the addition of a material with large electro-optic and nonlinear coefficients such as lithium niobate. This work examines the heterogeneous integration of thin-film lithium-niobate (TFLN) on silicon-nitride PICs. Bonding approaches are evaluated based on the interface used (SiO₂, Al₂O₃ and direct) to form hybrid waveguide structures. We demonstrate low losses in chip-scale bonded ring resonators of 0.4 dB/cm (intrinsic Q = 8.19 × 10⁵). In addition, we are able to scale the process to demonstrate bonding of full 100-mm TFLN wafers to 200-mm Si₃N₄ PIC wafers with high layer transfer yield. This will enable future integration with foundry processing and process design kits (PDKs) for applications such as integrated microwave photonics and quantum photonics.