Low-temperature bonding of HCl-dipped Ge substrate with diamond heat-spreader through atomically thin layer

Although Germanium devices have attracted attention for post-silicon device applications, they suffer from heat dissipation problems that hinder miniaturization. This study demonstrates the low-temperature and vacuum-free bonding of a germanium substrate with a diamond heat spreader, which has the highest thermal conductivity among solid materials. For efficient heat dissipation, we designed a bonding process at 200 °C using a reduction pre-bonding treatment instead of conventional oxidation. The process suppresses the formation of a germanium oxide layer at the bonding interface. This study demonstrates that germanium and diamond substrates are bonded through a 1.6-nm-thick amorphous intermediate layer. The shear stress reached 9.43 MPa, satisfying the MIL-STD-883E standard for microelectronics. As the germanium substrate can form atomic bonds with thermally conductive materials through a thin interfacial layer, it is expected that the bonding process of the HCl-dipped Ge device can contribute to future high-frequency devices.