Simulation and measurement of residual stress and warpage in a HgCdTe-based infrared detector at 100 K

Abstract

A thermomechanical analysis on a 320 × 256, 30 μm pitch, middle wave infrared detector operating at 100 K is conducted. The stress induced in the HgCdTe single crystal layer needs to be minimized to avoid electro-optical perturbations and the planarity of the detector has to respect strict optical requirements. The work includes stress determination by X-ray-diffraction (XRD), warpage measurements with laser scanning, analytical calculation and finite-element modelling. The hybridized detector is studied both alone and after being glued to an AlN hosting substrate. The results show that the initial stress in HgCdTe at room temperature is biaxial for all samples, with either tensile or compressive values (±10 MPa), mainly due to the lattice mismatch during epitaxy from CdZnTe. A stress increase of +45 MPa is induced after cooling to 100 K, with a maximum value of 57 MPa. The warpage of the hybridized circuit is then about 2.5 μm and is reduced after being glued to the hosting substrate. Finally, the model is used to extrapolate the behavior of such a detector for larger formats until 2 K 2 ; there is no significant impact on the stress in the HgCdTe layer, but warpage increases proportionally to the squared diagonal of the detector.

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