Low-temperature direct bonding of strengthened glass chips for optical imaging and co-packaged optics

Corning Gorilla glass is a well-known strengthened alkali aluminosilicate glass for its excellent optical, electrical, and mechanical properties. Recently gorilla glass has not only been extensively used for mobile devices as protective screens due to strengthened toughness, but many applications in optical imaging for AR devices and optical substrates for Co-packaged Optics also get plenty of interest. In this case, glass bonding is necessary for the optical imaging system, glass substrate lamination, and device encapsulation. Conventional fusion bonding of glass/glass chips generally involves a high temperature (> 600°C) near the glass transition temperature (Tg = 620°C for Gorilla Glass) to obtain strong bonding strength. Such a high-temperature process will inevitably result in the distortion of micro or nano structures. In this paper, we develop a low temperature direct bonding method. After standard industrial chemical cleaning (Piranha solution and RCA1 solution), we use water as bonding intermedia and bond two glass chips together at 200°C with very strong pull tensile strength (>10MPa) and superior optical transmittance (>91%, close to the bulk glass). The bonding mechanism is considered dehydration condensation. According to bonding interface characterization, the water interlay plays an important role in the bonding process by overcoming warpage and softening the surfaces to increase bonding area. This method also can be used to bond other glass materials for Electro-optical Circuit Boards, lab-on-a-chip, and MEMS/NEMS applications.