Interfacial phase transitions and bonding in the Cu/Al₂O₃system

We have studied the microstructure and structure of the interfacial region in the Cu/Al2O3 system bonded using the gas—metal eutectic process. Using a number of different contrast modes in the transmission electron microscope, we have shown that there exists a very thin amorphous interfacial phase, and this has been identified as a Cu—Al—O glass. We propose a simple mechanism to explain the formation of this glassy phase at the interface. On annealing, this glass crystallizes to the CuAlO2 and CuAl2O4 phases, which in turn, can decompose to Cu, Al2O3 and Cu2O, depending on the local oxygen concentration. The bond strength is reduced by about 25% on annealing, corresponding to the appearance of the crystalline interfacial phases.