Fabrication of heterogeneous LNOI photonics wafers through room temperature wafer bonding using activated Si atomic layer of LiNbO₃, glass, and sapphire

We proposed a room-temperature wafer-bonding method using activated Si atomic layer and verify its effectiveness for the fabrication of glass- or sapphire-based LiNbO₃-on-insulator (LNOI) devices for radio-frequency photonic applications. Four-inch LiNbO₃ was successfully fabricated on glass or sapphire wafers using the proposed method. The tensile strength of the fabricated wafers exceeded 23 MPa, which indicates that the bond between the LiNbO₃ and glass or sapphire wafers was strong. Atomic-structure analysis of bonding interfaces confirmed the effectiveness of the activated Si atomic layer as an adhesive for both LiNbO₃/glass and LiNbO₃/sapphire. In addition, the amorphous Si atomic layer existing at the bonding interface showed high transmittance over a wide range of wavelength, including the near-infrared region used for communication. The results demonstrate the potential of the proposed wafer-bonding method for the fabrication of LNOI devices used in optical communications, including broadband traveling-wave modulators.