The established technological standards, architectures, and material choices in the realm of advanced infrared (IR) imaging has enabled the design of high-resolution and high-range IR focal plane arrays (IRFPAs) while minimizing the cost, size, weight, and power consumption of the device. HgCdTe (MCT) has also emerged as the standard choice for the IRFPA device's detector layer as semiconductor material due to its high performance-to-cost, ability to operate optimally at extreme temperatures, and access to new application domains like two-color, active, and passive shortwave infrared (SWIR) imaging. Recent work has focused on a thermomechanical-stress-aware approach for advanced integration of IRFPAs leading to the design of Modified Direct Bond Interconnect (MoDiBI) integration technology which offers the possibility to venture toward design and fabrication of small pixel pitch, large format IRFPAs with longer term operational reliability. In the thermomechanical stress aware approach, finite element modeling is used to predict the effects of cyclic thermal load on the device's components. The device's geometry and materials are optimized based on the prediction.
Hitherto, however, such thermomechanical-stress-aware design has been focused on the detector-readout assemblies. The effect of the IRFPA packaging on the overall IRFPA performance under thermal load remains underexplored. Typically, the packaging involves a Balanced Composite Structure (BCS) sandwiched between the detector chip and the base plate for improving the thermomechanical reliability. In this work, we discuss the impact material choices in BCS has on the induced thermal stresses in critical components of the detector-readout assembly. We show that for an existing intricate and non-linear interplay between the detector chip, Si ROIC, and the BCS components, it may be beneficial to tune the thickness of the Si ROIC and to consider multi-parameter geometry and material optimization for designing IRFPA and packaging assemblies with optimal thermal performance. Further, we also suggest the novel material properties within the BCS stack that yield optimal thermomechanical response in the detector chip for chosen device configurations.
HgCdTe-based FPAs that can be used in high neutron radiation environments were designed and fabricated by EPIR, and tests using Fermi National Accelerator Laboratory’s neutron beam confirmed that these FPAs can maintain imaging functionality while exposed to fluxes up to low-1E13 neutron per squared centimeter accumulated neutron exposure. Monte Carlo N-Particle (MCNP) simulations were used to find that the energy deposited into the HgCdTe FPA can come from not only directly impinging neutrons but also scattered neutrons and subsequently generated protons, electrons and photons, confirming that our neutron-hardened designs are also hardened against other high energy particles. To mitigate radiation damage, we redesigned the optical system of the camera using modeling and simulation by utilizing MCNP code during our camera design. By properly choosing mirror substrate material and coating as well as the corresponding optical system and the camera design, we can filter out harmful radiation flux while still collecting the MWIR signal with high efficiency, thereby significantly reducing camera and image system performance degeneration under high-energy high-flux neutron beams.
Several MWIR nBn HgCdTe devices grown on silicon were studied. While several parameters are varied in the study, the devices can most usefully be put into 2 groups: those with a type 3 HgTe/CdTe superlattice barrier and those simply with a wider bandgap alloy barrier. Other groups have shown the potential advantage of a super-lattice barrier. Many devices were grown and fabricated, and were run through several optical and electrical tests to evaluate their properties. Utilizing the finite volume method based semiconductor device modeling software Devsim, these devices were simulated to extract further material parameters.
Pixel pitch size reduction was not the focus in early infrared (IR) detector development for a long time with pixel pitch remained at 24 μm or above. Pitch size reduction today is the key enabler for cost-efficient manufacturing of large format arrays and allows compact IR-systems with high spatial resolution. When mastered the smaller pixel pitch geometries will provide consistent range performance in a smaller package, minimized aliasing and false alarm rates, ability to use faster F/# optics and shorter focal length for long range identification and optimized size, weight and power (SWaP) characteristics. Advanced integration technologies (including three-dimensional integration) are necessary to realize small pitch arrays.
EPIR, Inc. has developed thermomechanical stress aware approach for advanced integration of IR focal plane arrays (IRFPAs) – MoDiBI. As intended, MoDiBI allows for favorably addressing the reliability concerns associated with the conventional integration approaches. The current work focuses on extending MoDiBI to small pixel pitch, large format IRFPA integration. Strategies for optimizing the thermal stress induced in the hybridized assembly during thermal cycling, thereby helping in reducing the fatal failures experienced by IRFPAs will be discussed. Applicability of MoDiBI to 1280×720, 8µm pitch IRFPAs will be presented.
Novel integration method that addresses thermo-mechanical reliability of the IRFPA hybrid assembly in advanced three-dimensional integration scheme requires optimization by engineering materials used for vertical integration and geometry engineering of the assemblies to be integrated. We present such optimization scheme and applicability of this method to vertical integration of HgCdTe and Type-II Superlattice (T2SL) based IRFPA.
Conference Committee Involvement (3)
Infrared Sensors, Devices, and Applications XV
3 August 2025 | San Diego, California, United States
Infrared Sensors, Devices, and Applications XIV
20 August 2024 | San Diego, California, United States
Infrared Sensors, Devices, and Applications XIII
22 August 2023 | San Diego, California, United States
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