Monolithic Multi-Metallic Thermal Expansion Stabilizer for IR Sensors
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Solution Overview
Problem
Infrared sensor chip assemblies face failures due to thermal cycling and coefficient of thermal expansion (CTE) mismatches between silicon readout integrated circuits (ROIC) and mercury cadmium telluride (HgCdTe) detector arrays, with existing solutions being costly and labor-intensive or causing performance degradation.
Innovation Solution
A monolithic multi-metallic thermal expansion stabilizer (MTES) with a CTE differential between two surfaces and a transition region, manufactured using additive manufacturing, is used to match the contraction rates of ROIC and HgCdTe detector arrays, reducing strain on interconnects by varying metal compositions along an axis to mitigate CTE differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If titanium and silicon shims are adhesively bonded to the back of the sensor chip assembly to achieve CTE matching, then the CTE compatibility between ROIC and platform is improved, but the manufacturing cost and labor intensity increase significantly
Solution Approach 1:
The patent changes the CTE parameter of the ROIC by bonding a CTE compensating shim made of specific metal alloys (such as Invar, Konstanz, or Elinvar) to the back of the ROIC. This allows the ROIC to maintain dimensional stability during thermal cycling by compensating for the CTE mismatch between the ROIC and the HgCdTe detector array, thereby improving reliability without requiring expensive manual die-level processes.
Solution Approach 2:
The patent uses composite material structures by bonding dissimilar metals (the ROIC substrate and the CTE compensating shim made of specific metal alloys) together to create a bimetallic structure. This composite structure exploits the different CTE properties of the two materials to achieve overall CTE matching with the detector array, resolving the contradiction between reliability and ease of manufacture.
2Ease of operation
If indium interconnects are used to hybridize ROIC to HgCdTe detector arrays, then the electrical connection is achieved, but the interconnects fail due to thermal cycling and CTE mismatch
Solution Approach 1:
The patent applies preliminary anti-action by pre-compensating for thermal expansion differences between the ROIC and detector array using a CTE compensating shim bonded to the ROIC back. This preliminary compensation prevents excessive stress from developing in the indium interconnects during thermal cycling, thereby protecting them from fatigue failure while maintaining their electrical connection function.
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
The MTES effectively reduces interconnect failure by matching the contraction rates of ROIC and HgCdTe detector arrays, thereby enhancing the reliability and longevity of infrared sensor chip assemblies.
Implementation Method 1
the coefficient of thermal expansion (CTE) mismatch between ROIC and HgCdTe
Implementation Method 2
causing the contraction of silicon readout integrated circuits (ROIC) to match contraction of a detector
Implementation Method 3
produced using additive manufacturing (e.g., a two-parameter laser powder metal additive manufacturing process)
Implementation Method 4
manufactured using ultrasonic additive manufacturing (AM) to ultrasonically weld thin layers together
Data Source
AI summary
A monolithic multi-metallic thermal expansion stabilizer (MTES) has a coefficient of thermal expansion (CTE) differential between a first surface and a second surface, and a transition region extending between for mitigating the CTE differential.