Thermal Stress Structural Optimization of InSb Infrared Focal Plane Array Detector

In liquid nitrogen shock experiments, a thermal mismatch occurs owing to the difference in the linear expansion coefficients of the layered In antimonide infrared focal plane array detector, and the excessive thermal mismatch stress fractures the InSb chip. Based on the calculation theory of the thermal stress suitable for the elastic multilayer system, employing the design method of a balanced composite structure is considered to be effective in reducing the impact of the thermal mismatch on the InSb chip. Accordingly, we optimize the thermal strain on the upper surface of the balanced composite structure. In other words, the optimization involved making the thermal strain on the upper surface of the Readout circuit in the balanced composite structure as close as possible to the thermal strain on the lower surface of the InSb chip. Consequently, the reduced thermal mismatch reduces the thermal stress in the InSb chip. Considering the maturity of the device processing technology, the thickness of the readout circuit is set at 25 μm, which is the thinnest sheet of the readout circuit fabricated in our lab using the chemical mechanical polishing method. For the defined thickness (25 μm) of the readout circuit, the calculation results indicate that the thermal strain on the upper surface of the readout circuit is the closest to the thermal strain on the lower surface of the InSb chip. When these two structures are glued together by the underfill, the tensile stress accumulated in the InSb chip is the smallest. The significant reduction in the tensile stress in the InSb chip provides a reliable structural design scheme and an implementation approach to reduce the fragmentation probability of the InSb chip in the liquid nitrogen impact.