Deformation modeling of InSb IRFPAs under liquid nitrogen shock

Abstract

The deformation appearing in InSb infrared focal plane arrays (IRFPAs) as subjected to liquid nitrogen shock tests, is an important criterion to assess the reliability of the structure designed and to predict the number of thermal cycling after which no cracks appear in InSb IRFPAs. After analyzing both the deformation distribution and the deformation running directions appearing in InSb IRFPAs at 77 K, we assume that the thermal strain accumulated in the liquid nitrogen shock test is completely relaxed. Based on this assumption and according to the temperature rising curve, we may obtain the deformation distribution in InSb IRFPAs at room temperature, which is identical in the deformation charactristics to the photograph of InSb IRFPAs taken at room temperature. After comparing the simulated liquid nitrogen shock tests (which InSb IRFPAs experience), with its fabrication process, we can infer that the square checkerboard buckling pattern appearing in the top surface of InSb IRFPAs originates from the residual stress and strain generated in the process of insufficient cures. And the deformation amplitude decreases with decreasing temperature of InSb IRFPAs in the nitrogen liquid shock tests. At 77 K, the deformation amplitude reduces to zero. This state corresponds to our assumption, that the accumulated stress and strain disappears. When the temperature of InSb IRFPAs increases from 77 K to room temperature, the square checkerboard buckling pattern will reappear in the top surface of InSb IRFPAs. These findings are beneficial to the optimization of the structure of InSb IRFPAs and to the improvement of the number of thermal cycling experienced by InSb IRFPA without cracks generated from liquid nitrogen shock tests.