Study of thermal stresses in InAs/GaSb type-II superlattice focal plane arrays via multi-scale finite element modeling

The thermal stress, significantly impacting the performance of infrared detectors, is typically caused by the thermal mismatch between adjacent materials. This presents a complex physical picture for InAs/GaSb type-II superlattice focal plane arrays, as it requires an analysis across multiple scales, from millimeter-scale device structures to micron-scale mesa-structured pixels. In this paper, an innovative multi-scale finite element model for InAs/GaSb type-II superlattice infrared focal plane array detectors has been developed, revealing the equivalent stress and its distribution along the mesa sidewall for the first time. Based on the specific boundary displacement method, an InAs/GaSb type-II superlattice infrared detector with 320 × 256 micro-mesa arrays is built, and the impact of various structural parameters, including pixel sizes, channel widths, indium bump diameters, and mechanical properties of underfill, on the pixel stresses is investigated. Simulation results indicate that, for the same pixel, the equivalent stress of the sidewall is higher and more sensitive to structural parameters compared to that of the planar surface. Our research offers a novel approach for the accurate and efficient simulation of thermal stresses in infrared detectors with mesa structures and provides valuable guidance for analyzing failure mechanisms and optimizing low-stress designs in InAs/GaSb type-II superlattice focal plane infrared detectors.