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.