Direct‐bonded Al/Al2O3 using a transient eutectic liquid phase.

Directed bonding with Al and Al2O3 was achieved using a transient liquid phase (TLP) method after annealing at the low melting point of Al, which deposited Ni, Cu, Ge, and Si on the Al2O3 substrate. Al/Al2O3 microstructures were evaluated using a scanning electron microscopy and transmission electron microscopy. A reaction layer was absent at the Al/Al2O3 interface, and all deposited metal films dissolved into the Al foil and reacted with Al to form an eutectic liquid phase near the interface to wet and join with the Al2O3. Al9Fe2 and Al3Fe intermetallic compounds were formed in the Al substrate because of Fe precipitation, which is an impurity of Al foil, and the reaction with Al at the grain boundaries of Al. The bonding area percentage, shear strength, and thermal conductivity for Al and Al2O3 were assessed using scanning acoustic tomography (SAT), the ISO 13 124 shear strength test, and the laser flash method, respectively. The Al/Al2O3 specimen deposited with the Ni film had the highest shear strength (33.74 MPa), thermal conductivity (42.3 W/mK), and bonding area percentage (96.78%). The Al/Al2O3 specimens deposited with Ge and Si exhibited relatively poor bonding because of the oxidation of Ge and Si at the surface of Al2O3 before bonding with Al. [ABSTRACT FROM AUTHOR]