VUV/O3 activated direct heterogeneous bonding towards high-performance LiNbO3-based optical devices

The combination of lithium niobate (LiNbO3) and glass without an intermediate layer is an essential component of micro/nanofluidics and optical waveguides. Direct bonding is a popular method for joining homo/heterogeneous materials into a single composite. However, direct bonding of LiNbO3 and glass is extremely difficult due to the chemical inertness of LiNbO3 and the large mismatch of the coefficients of thermal expansion of these materials. In this work, we realized direct bonding of LiNbO3 and glass via VUV/O-3 activation at 150 degrees C. Focused ion beam microfabrication tests and observation by scanning electron microscopy and transmission electron microscopy confirmed the strong LiNbO3/glass bonding interfaces. The excellent transmittance and piezoelectric properties of the direct bonded pairs and the single-crystal orientation of the LiNbO3 close to the glass demonstrated that the VUV/O-3 activated direct bonding method was suitable for the fabrication of high-performance surface acoustic wave (SAW)-actuated LiNbO3-based devices. Additionally, we investigated the bonding mechanism through water contact angles, atomic force microscopy, Raman spectroscopy, FTIR spectroscopy, and adhesion measurements.