Heterogeneous Back‐End‐of‐Line Integration of Thin‐Film Lithium Niobate on Active Silicon Photonics for Single‐Chip Optical Transceivers

ABSTRACT The explosive growth of artificial intelligence, cloud computing, and large‐scale machine learning is driving an urgent demand for short‐reach optical interconnects featuring large bandwidth, low power consumption, high integration density, and low cost adopting complementary metal‐oxide‐semiconductor (CMOS) processes. Heterogeneous integration of silicon photonics and thin‐film lithium niobate (TFLN) combines the advantages of both platforms, and enables co‐integration of high‐performance modulators, photodetectors, and passive photonic components, thereby offering an ideal route to meet these requirements. However, process incompatibilities have constrained the integration of TFLN to passive silicon photonics only. Here, we demonstrate the first heterogeneous back‐end‐of‐line integration of TFLN with a full‐functional active silicon photonics platform via trench‐based die‐to‐wafer bonding. This technology introduces TFLN after completing the full CMOS‐compatible silicon photonics process. The close vertical proximity of the Si and TFLN waveguides enables efficient inter‐layer optical coupling without fine patterning on the TFLN layer. Si/SiN passive components including low‐loss fiber interfaces, 56‐GHz Ge photodetectors, 100‐GHz TFLN modulators, and multilayer metallization are integrated on a single silicon chip. The integrated on‐chip optical links exhibit >60 GHz electrical‐to‐electrical bandwidth and support 128‐GBaud OOK and 100‐GBaud PAM4 transmission below forward error correction thresholds, establishing a scalable platform for energy‐efficient, high‐capacity photonic systems.