Angular Dependence of Surface Energy with Crystal Directions of LiNbO₃ (110) for Nano-Bonding^TM to Si and α-quartz SiO₂

LiNbO₃ is a piezo-electric that, when mono-lithically integrated to Si-based materials, yields voice activated chips.

Current bonding methods include hetero-epitaxy and Direct Wafer Bonding (DWB). However, hetero-epitaxy causes lattice strain, since the lattice constant of LiNbO₃ is heavily mismatched with Si (100) and α-quartz SiO₂ (100). Thermal expansion mismatch during DWB causes fractures of LiNbO₃. Also, LiNbO₃ decomposes into Li₂O₅ and Li⁺ at T > 493K. Instead, this work uses Nano-Bonding^{TM, 1} (NB) and Surface Energy Engineering to modify surface energies into ‘far-from-equilibrium’ states so that when nano-contacted, a 2D-precursor phase forms to catalyze bonding.

Three Liquid Contact Angle Analysis (3LCAA) can map different angular directions on 6” LiNbO₃ (110), Si (100), and α-quartz SiO₂ (100) wafers. Water contact angles are found to vary significantly, by 50%, from 41.8 ± 1.5° to 59.8 ± 1.5°, as a function of crystal direction. Correlation between surface structure and surface energies along different crystal directions will be discussed.

¹ Herbots et al. US Pat. 6613677 (2003), 7,851,365 (2010), 9,018,077 (2015), 9,589,801 (2017), pend. (2020)