Plasma activated titanium-based bonding for robust and reliable Si–Si and Si-glass integration

Abstract

The exceptional biocompatibility of Ti/Ti bonding technology makes it highly significant for the sealing of implantable devices. However, achieving highly reliable Ti/Ti bonding at low temperatures is challenging due to the facile formation of a native oxide film, which hinders the diffusion of interfacial atoms. This paper develops a low-temperature Ti/Ti bonding process based on plasma activation, resulting in a remarkable bonding strength of 17.5 MPa at 300 °C, which can be used for Si–Si homogeneous and Si-glass heterogeneous integration. After optimizing the processes, the surface oxides of Ti can be partially reduced through Ar/H2 plasma activation to form unsaturated chemical bonds, thereby overcoming the limitation of film thickness in Ti/Ti bonding. The results indicate that plasma activation can realize high strength Ti/Ti bonding in the film thickness range of 10–50 nm. It is worth noting that the Ti/Ti bonding area and strength remain stable after immersion experiments in DI water and normal saline for 7 days, which proves that Ti/Ti bonding has good corrosion resistance. In addition, the microcavity structures were prepared using photolithography and etching techniques. The Ti/Ti bonding technology enables direct bonding of microcavity structures with plate Ti, and an intact bonding interface near the microcavity was obtained. This low-temperature Ti/Ti bonding technology is suitable for the three-dimensional integration of various substrate materials, and its excellent corrosion resistance makes it promising for application in the sealing of BioMEMS.