Multilayer CdHgTe-based infrared detector: 2D/3D microtomography, synchrotron emission and finite element modelling with stress distribution at room temperature and 100 K

Abstract

The mechanical behaviour of a CdHgTe-based infrared detector was evaluated after processing at several temperatures to determine the impact of thermomechanical loading on residual stress and reliability. The architecture of the detector was first entirely characterized, relying on SEM, X-ray microtomography and diffraction analysis, in order to get the nature, the morphology and the crystallographic orientation of all the constitutive layers, and in particular the indium solder bumps. The results notably showed the unexpected single crystal aspect of the indium bumps with a repeatable truncated cone geometry. To obtain the thermomechanical response of the structure after processing and in the range of operating temperatures (from 430 K to 100 K), a 3D Finite Element model was then developed. As expected, the numerical results showed a stress gradient evolution in the structure from high to low temperatures, with high loca njvvl stress around 30 MPa in the CdHgTe at 100 K, mainly due to the thermal expansion coefficient mismatch between the different layers. They highlighted the significant influence of the geometry and the single crystal nature of the bumps as well as the behaviour law of the different materials.