Direct bonding of III-V detectors to silicon for infrared focal plane arrays

L3Harris Technologies recently patented infrared detector arrays made by directly bonding a III-V Type II Superlattice (T2SL) detector to an optical silicon wafer. The process is performed at the wafer level and can replace L3Harris' traditional adhesive bond. Direct bonding offers several advantages over adhesive bonding. First, higher operability and fewer defect clusters result due to the rigorous preparation of wafer surfaces before bonding. The number of antireflection coated surfaces is decreased from three to one. Higher quantum efficiency results from the improved transmission through the III-V/Si interface. This is critical for multi-band detectors, which operate over a relatively wide spectral bandwidth. Finally, the bond withstands higher processing temperatures than the adhesive bond. The process has been demonstrated on 150mm silicon with III-V wafers up to 125mm in diameter. The optical silicon remains in the finished focal plane array (FPA), serving as a protective window on the front surface of the delicate detector array. The silicon is a key component to L3Harris FPAs, forcing a coefficient of thermal expansion (CTE) match between the detector array and the silicon readout integrated circuit. The CTE match enables large array formats and long thermal cycle life without shimming.