Balanced Composite Structure Thermal Mismatch Cracking
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Solution Overview
Problem
Traditional approaches for shimming readout integrated circuits (ROICs) face challenges in maintaining a good thermal match across a wide temperature range, particularly from cryogenic to elevated temperatures, due to significant deviations in thermal expansion coefficients between dissimilar materials used in the balanced composite structure (BCS) and epitaxial materials.
Innovation Solution
The use of a balanced composite structure (BCS) with a GaSb substrate and a silicon layer, where the primary shim material matches the thick remaining material on the array side, achieving a wide range of thermal match by closely tracking the thermal expansion of the pure core material, and utilizing GaSb or InAs/GaAs as core materials to ensure effective thermal matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional metal BCS (titanium, stainless steel, germanium) is used for thermal matching, then the average CTE or final linear displacement can be matched, but significant deviations occur over the temperature range due to fundamental differences in CTE
Solution Approach 1:
The patent employs a balanced composite structure (BCS) consisting of multiple layers including a semiconductor substrate, buffer layer, device layer, and cap layer. This composite structure is designed to match the thermal expansion characteristics of the focal plane array across a wide temperature range, resolving the contradiction between achieving precise thermal matching and maintaining adaptability across varying temperatures.
Solution Approach 2:
The patent modifies the BCS composition and layer thicknesses to change the thermal expansion parameters. By adjusting the CTE of individual layers and their proportions, the overall BCS achieves both precise thermal matching at operating temperatures and adaptability across the full temperature range from cryogenic to elevated conditions.
2Manufacturing precision
If dissimilar materials are used for BCS core material and epitaxial material, then average CTE may match, but significant deviations occur over temperature range
Solution Approach 1:
The patent uses homogeneous materials within each BCS layer (semiconductor substrate, buffer layer, device layer, cap layer) to ensure uniform thermal expansion characteristics. This homogeneity prevents local stress concentrations and maintains consistent thermal matching reliability across the entire temperature range, eliminating deviations that occur with dissimilar material combinations.
3Ease of manufacture
If bond layer between silicon and residual epi material is used, then connection is achieved, but transmission losses occur due to IR absorption by bonding agents
Solution Approach 1:
The patent removes or minimizes the bond layer between the silicon substrate and the residual epitaxial material. By extracting this problematic bonding interface, the design eliminates IR absorption losses while maintaining structural integrity through alternative bonding methods or direct contact between compatible surfaces.
Solution Approach 2:
The patent introduces an intermediary layer or modification to the bonding interface that allows mechanical connection between silicon and epi material without introducing IR-absorbing bonding agents. This intermediary enables both manufacturing ease and optical transparency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in a robust thermal match over an extended temperature range, reducing transmission losses and maintaining performance across varying temperatures, as demonstrated by the similarity in linear expansion data and improved FPA performance with reduced cracking and enhanced connectivity.
Implementation Method 1
the primary shim material matches the thick remaining material on the array side, achieving a wide range of thermal match by closely tracking the thermal expansion of the pure core material
Data Source
AI summary
A device and method of manufacturing are disclosed. The device contains a buffer layer containing a first material, a detector structure disposed above the buffer layer, a readout integrated circuit coupled with the detector structure, a layer above the readout integrated circuit comprising a second material, and a silicon layer above the layer.