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.
L3Harris has developed a multispectral sensor architecture that opens doors to the incorporation of enabling functionality for future applications. This sensor architecture, while detector material agnostic in nature, builds upon our type-II superlattice (T2SL) technology, which was originally developed through the tri-service Vital Infrared Sensor Technology Acceleration (VISTA) program. The sensor architecture consists of stacked absorber layers that can be individually processed as they are integrated into the sensor stack. This layer-based approach enables the insertion of additional functional structures to enhance performance, such as embedded dielectric filters for efficient spectral separation, which would not be possible in a monolithic design. Due to the additional degrees of freedom with this configuration, it is necessary to design the filter such that it is compatible with the process required to functionalize each absorber while simultaneously meeting performance requirements. In this work, we report on various filter designs impacting the performance of focal plane arrays (FPAs) having embedded dielectric filters, under various practical constraints.
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