Low Pressure Sensor Rigid Island Diaphragm Design
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Solution Overview
Problem
Traditional low-pressure sensors with uniform-thickness diaphragms suffer from significant non-linearity, mechanical damage, and increased die size, making them impractical for high-sensitivity applications.
Innovation Solution
A low-pressure sensor design featuring a sensor die with a cavity and a rigid island, where the cavity includes a peripheral groove creating a thin area for a stress-sensitive circuit, and a cap for protection, which reduces non-linearity and mechanical stress, allowing for smaller die size and increased sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the diaphragm linear dimension A is increased to improve sensitivity, then the output signal increases, but the die size increases and cost increases
Solution Approach 1:
The patent applies local quality by creating a non-uniform diaphragm thickness distribution through rigid islands. The diaphragm has thin regions (for high sensitivity and deflection) and thick regions (for structural support), allowing high sensitivity without proportionally increasing overall die size. The thin area is localized to where stress sensing is needed, while rigid islands provide support in other areas.
2Measurement precision
If the diaphragm thickness d is decreased to improve sensitivity, then the output signal increases, but the non-linearity increases significantly
Solution Approach 1:
The patent resolves the linearity-sensitivity contradiction by making the diaphragm thickness non-uniform. Thin areas provide high sensitivity to pressure changes, while thick rigid islands maintain structural integrity and reduce non-linear deflection. This local variation in thickness allows the sensor to achieve high sensitivity without the excessive non-linearity that would result from uniformly thinning the entire diaphragm.
Solution Approach 2:
The patent effectively creates a composite structure by combining thin diaphragm regions with rigid island regions within the same diaphragm. This composite approach allows different parts of the diaphragm to serve different functions: thin areas for sensing sensitivity and thick areas for mechanical stability, thereby reducing overall non-linearity while maintaining high sensitivity.
3Measurement precision
If the diaphragm thickness d is decreased to improve sensitivity, then the output signal increases, but the mechanical strength decreases leading to damage
Solution Approach 1:
The patent applies local quality by creating regions of different thicknesses within the diaphragm. Thin areas are localized to where pressure sensing is required, while thick rigid islands are positioned to provide mechanical support and strength. This allows the diaphragm to achieve high sensitivity in thin regions without compromising overall mechanical integrity, as the thick rigid islands prevent excessive stress concentration and potential failure.
4Ease of manufacture
If a uniform-thickness diaphragm is used to simplify manufacturing, then the manufacturing process is easier, but the non-linearity is significant
Solution Approach 1:
The patent resolves the contradiction between manufacturing simplicity and linearity by using rigid islands to create localized thickness variations. Rather than requiring complex non-uniform thinning across the entire diaphragm, the manufacturing process adds rigid islands to specific locations, which is achieved through standard semiconductor fabrication techniques. This approach maintains relative manufacturing simplicity while significantly improving linearity through the structural support provided by the rigid islands.
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 design achieves improved linearity and sensitivity while minimizing die size and mechanical damage, enabling more efficient and cost-effective low-pressure sensing.
Implementation Method 1
MEMS piezoresistive pressure sensors typically have a diaphragm and piezoresistors located on the diaphragm. When a pressure drop is applied to the diaphragm, the diaphragm bends, and resistance of the piezoresistors changes as a result of bending stress.
Data Source
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AI summary
A device/method for sensing a physical parameter, including a sensor die and a stress-sensitive circuit. The sensor die includes a semiconductor substrate and a cavity that creates an elastic element that bends in response to the physical parameter exerted on the sensor die. The elastic element includes at least at least one rigid island formed within the cavity, a thin area surrounding the at least one rigid island and having smaller thickness than the rigid island, and at least one stress concentrator at least partially formed in the thin area of the elastic element on the side of the substrate opposite the cavity. The stress-sensitive circuit includes at least one stress-sensitive component formed in the thin area of the elastic element. The at least one stress concentrator increases stress in the locations of the at least one stress-sensitive component resulting in an increase of the device sensitivity to the physical parameter.