Progress in heterogeneous integration of LiNbO₃ and LiTaO₃ thin films for advanced piezoelectric and optoelectronic applications

Lithium niobate (LiNbO₃) and Lithium tantalate (LiTaO₃) are renowned for their outstanding electro-optical, nonlinear optical, and piezoelectric properties, making them indispensable in high-speed optical communications, integrated photonics, RF front-end modules, and infrared sensing technologies. To meet the growing demand for higher integration density and multifunctionality in modern optoelectronic systems and by leveraging the complementary strengths of those photonic materials, the heterogeneous integration of LiNbO₃ or LiTaO₃ thin films onto easier manufacturable and less exotic substrates, such as silicon, silicon carbide, and compound semiconductors, has emerged as a compelling approach for realizing versatile and high-performance electronic-photonic system-on-chip (SoC) integration. This review provides a comprehensive overview of recent advances in LiNbO₃ and LiTaO₃ heterogeneous integration, with a focus on bonding techniques, including plasma-activated bonding, surface-activated bonding, and adhesive bonding. Key aspects, including interfacial properties, bond strength optimization, and the quality of transferred films, are critically examined. The paper also highlights the wide-ranging applications enabled by these integrated platforms, spanning electro-optical modulators, photonic integrated circuits, RF filters, and infrared detectors. Finally, the review discusses ongoing challenges in large-scale fabrication, material compatibility, and thin-film transfer processes, which are pivotal for the continued evolution of LiNbO₃ or LiTaO₃ hybrid systems. This work aims to offer a thorough understanding of integration technologies and their potential to drive the next generation of optoelectronic and photonic devices.

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