Evolutions of interfacial microstructures in Cu/SiO2 hybrid joints during temperature cycling tests

In this study, nanotwinned Cu (NT-Cu) and SiO2 hybrid joints were fabricated at 200 °C and subjected to thermal cycling tests (TCTs) up to 2000 cycles for the reliability evaluation. It is intriguing that the measured electrical resistance of the Cu–Cu joints decreased as the cycle number increased. Interfacial microstructure analyses were carried out by plan-view and cross-sectional scanning transmission electron microscope (STEM) to analyze the evolution of microstructures at the bonding interfaces and correlate with the increase in the electrical conductivity. Results showed that the bonding quality and conductivity of the NT-Cu/SiO2 hybrid joints were enhanced after the TCTs. The electrical resistance of the joints decreased by 18% after 2000 temperature cycles. Plan-view STEM images indicate the boning interface consisted of numerous discrete nanoscale voids for the as-fabricated Cu–Cu joints, and they merged into larger voids of approximately 100 nm in diameter through Ostwald ripening mechanism during thermal cycling. Furthermore, grain growth also occurred in the interface, resulting in excellent bonding interfaces.