Interface characteristics comparison of sapphire direct and indirect wafer bonded structures by transmission electron microscopy

Abstract In this paper, we demonstrate a hydrophilic sapphire wafer bonding method combining plasma-activation and high-temperature bonding process. It is successfully employed in two sapphire bonding structures, including sapphire direct bonding and sapphire indirect bonding based on an intermediate amorphous Al2O3 (a-Al2O3). Transmission electron microscopy (TEM) results show that the a-Al2O3 turns to be the single crystalline phase due to the induction of the sapphire substrate after high temperature bonding at 1000 °C. Moreover, high bonding strength is achieved for sapphire/sapphire (9.91 MPa) and sapphire/Al2O3/sapphire (17.96 MPa) structures and exceeds that of the bulk sapphire. This sapphire bonded structure with cavity can be applied to fabricate optical devices and pressure and temperature sensors for extreme high temperature environments.