The infrared focal plane arrays detector is a multilayer structure which is mainly composed of detector chip, Si-ROIC, and fan out layer. In view of the different thermal expansion coefficients between the material layers, considerable thermal stress will be generated in this device among the cooling cycle which could lead to physical breakdown of the chip under extreme circumstances. Models of finite element analysis (FEA) were established to explore the thermal stress of HgCdTe infrared focal plane devices at low temperature. According to the characteristics of the expansion alloy, the two kinds of focal plane device structures were simulated: one is that with invar layer below the Al2O3 piece, the other is that kovar layer between the Si-ROIC and Al2O3 pieces. Both of them can reduce the thermal stress effectively, and improve the reliability of IRFPAs detector.
Reliability is an important index to ensure the application of infrared focal plane arrays (IRFPAs) in complex environment, and it becomes a major bottleneck problem of IRFPAs’ development. Because of the characteristics such as type, nature, quantity, location and distribution et al, bad pixel which contains initial bad pixel and used bad pixel has outstanding advantage for failure analysis and reliability evaluation of IRFPAs. In this paper, the structure of IRPFAs has been introduced in detail, and the damage mechanisms of used bad pixel also have been analyzed deeply. At the same time, the feasibility to study IRPFAs' damage stress, failure position, damage mechanism has been discussed all around. The research of bad pixel can be used to optimize the structure and process, meanwhile it also can improve the accuracy of bad pixel identification and replacements.
Thermal cycling reliability is one of the most important issues whether the HgCdTe infrared focal plane array detectors can be applied to both military and civil fields. In this paper, a 3D finite element model for indirect hybrid HgCdTe infrared detectors is established. The thermal stress distribution and thermally induced warpage of the detector assembly as a function of the distance between the detector chip and Si-ROIC, the thickness and the materials properties of electrical lead board in cryogenic temperature are analyzed. The results show that all these parameters have influences on the thermal stress distribution and warpage of the detector assembly, especially the coefficient of thermal expansion(CTE) of electrical lead board. The thermal stress and warpage in the assembly can be avoided or minimized by choosing the appropriate electrical lead board. Additionally, the warpage of some indirect hybrid detectors assembly samples is measured in experiment. The experimental results are in good agreement with the simulation results, which verifies that the results are calculated by finite element method are reasonable.
Hybrid infrared focal plane array detector is always a heterogeneous components assembly. The thermal expansion
mismatch between the components, HgCdTe detector chip and silicon readout integrated circuit, combined with large
thermal variations (300 K-80 K), results in substantial thermal stress in the interconnection layer and large warpage of
the whole assembly. In this paper, the thermal stress distribution and warpage of the assembly are analyzed by finite
element method. The results show that the thickness of sapphire electrical lead board, Si-ROIC and GaAs substrate have
influences on the thermal stress distribution and warpage of the assembly, and the warpage is affected significantly.
Furthermore, we adopt the theoretical formula of multilayer structure to calculate the warpage of IRFPA module. The
simulation results are in good agreement with those obtained from the theory. In order to improve the reliability of the
IRFPA detector, the assembly is optimized according to the analysis result. After optimizing, the warpage of the assembly
decreases from -10.2 um to -5.5 um, the maximum Von Mises Stress in HgCdTe layer decreases by 15.5%, and the
uniformity of thermal stress distribution is improved effectively.