Ultra-Tough Copper-Copper Bonding by Nano-Oxide-Dispersed Copper Nanomembranes

Metal-metal bonding has played a pivotal role in advancing human technologies across various industrial sectors. As devices continue to miniaturize, there is an increasing need for efficient bonding techniques capable of achieving metal-metal bonds at smaller length scales. In this study, a facile but effective bonding technique is developed that enables the bonding of randomly oriented copper with copper nanomembranes under low temperatures and pressures. The fabricated copper nanomembranes, with a thickness of ≈50 nm and a width of 1 cm or above, exhibit a unique heterogeneous nanostructure, comprising copper nanocrystals along with nano-copper-oxide dispersions. Consequently, these copper nanomembranes display exceptional mechanical properties, including an ultra-low elastic modulus of ≈35 GPa, a remarkable yield strength of ≈1 GPa, and excellent ductility of ≈40%, overcoming the conventional strength-ductility trade-off observed in various copper alloys. Most importantly, these ultra-soft copper nanomembranes serve as metallic "glues", promoting grain growth across the bonding interface between randomly oriented copper surfaces. This process leads to an average interfacial shear strength of up to 73 MPa at room temperature, representing an approximate 35 times increase in bonding strength compared to direct copper-copper bonding achieved under identical temperature and pressure conditions.