Achieving high mechanical properties and outstanding thermally conductive Al/AlN direct-bonded joints through interfacial oxide barrier elimination

A novel low-temperature bonding approach via the Al-Si-Mg inactive interlayer was proposed to fabricate Al/AlN joints for the first time, achieving a shear strength of 105.2 MPa and a thermal conductivity as high as 216.1 W/(m·K). The joints comprised nanoscale Mg-Al-O compounds, α-Al, and Si phases. By the deoxidation reaction of Mg atoms in the interlayer with AlN_xO_y of the AlN surface, Mg₃Al₁₄O₂₄ was formed and the Al-N with a relatively high adsorption energy was exposed. Thus, the Al-N was bonding with Al to achieve a seamless and robust Al/AlN direct-bond interface. The influence of temperature on the mechanical properties and heat transfer characteristics of joints was systematically examined. By increasing the temperature to eliminate the primary Si, the joint strength peaked at 105.2 MPa, surpassing that of the metal/AlN joints brazed at higher temperatures by active brazing. Through adjusting the temperature to inhibit the diffusion of Si atoms, the lattice distortion of Al was decreased, and the best thermal conductivity reached 216.1 W/(m·K), far exceeding that of Cu/AlN joints using active brazing or other methods. This bonding approach provides a novel strategy for the high-performance manufacturing of AlN substrates.