Deposition of Ultra-thin Titanium (Ti) layer (3 nm) on Copper (Cu) surface inhibits surface oxidation upon exposure to ambient air as well as reduces surface roughness from about 2.1 nm (Cu only) to about 0.4 nm resulting in Cu-Cu bonding at a temperature as low as 160 °C and operating pressure as low as 2.5 bar. This simple passivation mechanism enhanced diffusion of Cu across the boundary and resulted in grain growth across the entire bonding layers as revealed by several methodical characterizations. This practical breakthrough has immense potential to usher us into practical realization of 3D IC integration. © 2016 Elsevier B.V.