Fabrication and photonic applications of Si-integrated LiNbO₃ and BaTiO₃ ferroelectric thin films

Silicon, renowned for its applications in electronic circuits, also offers significant advantages in the realm of integrated optics. While silicon does have inherent limitations in fabricating active devices, these challenges can be overcome through heterogeneous integration with other materials. Ferroelectric materials like lithium niobate (LN) and barium titanate (BTO) exhibit exceptional electrical and nonlinear optical properties, making them ideal candidates for integrated silicon photonics. Over the past few decades, the LN platform has made substantial progress, surmounting obstacles such as manufacturing difficulties, high waveguide losses, and low modulation bandwidth caused by wide electrode spacing. Consequently, LN-based devices have found widespread application in various fields. With the advent of high-quality, large-size LN on insulator wafers, LN photonics has become a burgeoning research area. At the same time, the ferroelectric material BTO, with its tremendous electro-optic response, shows promise for the next generation of integrated photonics. Recent studies have highlighted the remarkable performance of BTO-based modulators, which offer smaller device sizes compared to LN by achieving lower half-wave voltages. This comprehensive review presents various fabrication methods for integrating LN and BTO thin films on silicon, focusing on recent advancements. We discuss their electro-optic responses and provide an overview of the diverse applications enabled by these platforms. Finally, we summarize the current state of integrated LN and BTO photonics research and offer insights into future directions.