Polysilicon Coupling Layer for Pressure Sensor Strain Reduction
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Solution Overview
Problem
Conventional pressure sensors using aluminum layers to couple the top glass layer to the die experience strain issues due to thermal expansion mismatches and reduced elasticity, leading to decreased accuracy and potential leaks that affect the hermetic seal.
Innovation Solution
The use of a polysilicon layer instead of aluminum to couple the top glass layer to the die, which exhibits a similar thermal expansion coefficient to the die and is more elastic, minimizing strain and forming a more reliable hermetic seal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an aluminum layer is used to couple the top glass layer to the die, then the coupling strength is improved, but thermal expansion mismatch causes strain on the die and diaphragm, reducing measurement accuracy
Solution Approach 1:
The patent changes the material parameter (thermal expansion coefficient) by replacing aluminum with polysilicon. Polysilicon has a thermal expansion coefficient closer to that of the glass and die materials, reducing thermal mismatch strain while maintaining coupling strength. This parameter change resolves the contradiction between strong coupling and measurement accuracy.
Solution Approach 2:
The patent uses a composite structure with a polysilicon layer as the coupling material between glass and die. This composite approach combines the benefits of strong adhesion with compatible thermal expansion properties, eliminating the strain issues caused by aluminum while maintaining structural integrity.
2Strength
If an aluminum layer is used to couple the top glass layer to the die, then the coupling strength is improved, but the hermetic seal reliability deteriorates due to reduced elasticity and potential leaks
Solution Approach 1:
The patent changes the elastic properties parameter by using polysilicon instead of aluminum. Polysilicon maintains elasticity after bonding, allowing the structure to accommodate thermal and mechanical stresses without compromising the hermetic seal, thus improving reliability while maintaining coupling strength.
Solution Approach 2:
The patent eliminates the need for post-bonding leak testing and repair processes by using a material (polysilicon) that inherently prevents leaks. This approach treats the bonding interface as a permanent, leak-free connection, eliminating the need for additional quality control steps.
3Ease of manufacture
If an aluminum layer is used to couple the top glass layer to the die, then the manufacturing process is simplified, but post-manufacturing processing time increases due to leak testing and potential repairs
Solution Approach 1:
The patent performs preliminary action by selecting polysilicon as the coupling material before the bonding process. This material choice pre-prevents potential leak issues, eliminating the need for subsequent leak testing and repair operations, thus reducing post-manufacturing processing time while maintaining manufacturing simplicity.
Solution Approach 2:
The patent extracts the leak testing and repair operations from the manufacturing process by using a material that inherently prevents leaks. This removal of unnecessary post-processing steps reduces time loss while maintaining ease of manufacture.
4Strength
If an aluminum layer is used to couple the top glass layer to the die, then the coupling strength is improved, but the die and diaphragm experience strain leading to potential cracking
Solution Approach 1:
The patent changes the thermal expansion coefficient parameter by using polysilicon instead of aluminum. This material substitution reduces thermal mismatch strain on the die and diaphragm, maintaining coupling strength while preserving structural integrity and preventing cracking.
Solution Approach 2:
The patent applies local quality by using a material (polysilicon) with locally optimized properties at the bonding interface. The polysilicon layer provides both strong coupling and compatible thermal expansion characteristics, protecting the die and diaphragm from strain while maintaining the necessary mechanical strength.
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 polysilicon layer significantly reduces strain on the die and diaphragm, enhancing the accuracy of pressure measurements and providing a more reliable hermetic seal that minimizes leaks and post-manufacturing processing time.
Implementation Method 1
exhibits a similar thermal expansion coefficient to the die
Implementation Method 2
is more elastic, minimizing strain
Data Source
AI summary
An example pressure sensor comprises a die. The die comprises at least one lateral section and a diaphragm extending between opposing portions of the lateral section. The lateral section and the diaphragm define a top surface and the lateral section define a bottom surface opposite the top surface. The lateral section and the diaphragm partially define a first cavity. The pressure sensor further comprises a top glass layer positioned adjacent to a portion of the top surface. The top glass layer partially defines a second cavity adjacent to the diaphragm. The pressure sensor also comprises a polysilicon layer between the top glass layer and a corresponding portion of the top surface. The polysilicon layer couples the top glass layer to the die.