Overview of low temperature hydrophilic Ge to Si direct bonding for heterogeneous integration

Germanium is gaining interest in two important areas of electronics; for high performance metal oxide semiconductor field effect transistors due to the high carrier mobility and for imaging and optical applications due to its superior absorption in the infrared range. Optimally, germanium will be integrated with existing silicon electronics to enhance electrical and optical properties. One method for integration of germanium with silicon is direct wafer bonding of the two materials. In this paper, wafer-level germanium–silicon heterogeneous integration technologies are investigated and described in detail, including structural and electrical features of bonded hetero-structure.