Direct bonding of germanium and diamond substrates by hydrophilic bonding

Germanium (Ge) is attracting attention as a high-frequency device material, but its low thermal conductivity causes a heat dissipation problem. To overcome this drawback, we demonstrate the direct bonding of the Ge substrate with a diamond heat-dissipating substrate, which has the highest thermal conductivity among solids. The Ge substrate was activated by oxygen plasma, and the diamond substrate was washed with a mixture of NH
3
/H
2
O
2
, and then the two substrates were brought into contact with each other. The substrates were then heated at 200°C for 2 hours with a bond load of 3 MPa. The above process resulted in the direct bonding of the Ge and diamond substrates. This direct bonding improves the heat dissipation of Ge devices, which will contribute to next-generation high-speed devices.