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

Silicon nitride (Si3N4) is a versatile waveguide material platform for CMOS foundrybased 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 x 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.