Linear Capacitive Pressure Sensor With Spring-Driven Sliding
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Solution Overview
Problem
MEMS pressure sensors exhibit non-linear capacitance changes across a range of temperatures due to the nature of parallel plate capacitors and membrane displacement, leading to reduced sensitivity and accuracy, while using a rigid membrane to mitigate non-linearity compromises sensitivity and area efficiency.
Innovation Solution
A pressure sensor design featuring a membrane suspended over a cavity with a frame that translates out-of-plane movement into in-plane sliding movement via spring structures, utilizing comb-finger capacitors to measure lateral sliding, providing a linear capacitance output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a rigid membrane is used to reduce non-linearity, then non-linearity is reduced, but sensitivity and accuracy are reduced
Solution Approach 1:
The patent changes the geometric parameters of the membrane structure by introducing a central support pillar and optimizing the membrane thickness distribution. The membrane is made thinner at the center (where pressure displacement occurs) and thicker at the edges, with the central pillar providing localized support. This parameter optimization allows the membrane to achieve both reduced non-linearity and maintained sensitivity by controlling the displacement characteristics in different regions.
Solution Approach 2:
The patent segments the membrane structure by introducing a central support pillar that divides the membrane into distinct regions. This segmentation allows different parts of the membrane to have different thicknesses and mechanical properties, enabling the center to be more compliant for sensitivity while the edges provide structural stability for non-linearity reduction.
2Stability of the object's composition
If a rigid membrane is used to reduce non-linearity, then non-linearity is reduced, but area efficiency is reduced
Solution Approach 1:
The patent optimizes the membrane thickness parameter through the entire area, creating a non-uniform thickness distribution that is thinner at the center and thicker at the edges. This allows the membrane to achieve reduced non-linearity without requiring excessive area, as the thickness variation provides the necessary mechanical properties within a compact footprint.
3Device complexity
If parallel plate capacitors are used, then the sensor structure is simple, but capacitance change is non-linear across temperature range
Solution Approach 1:
The patent changes the geometric parameters of the capacitor structure by introducing a movable central support pillar that shifts the effective plate separation distance non-linearly in response to pressure. This geometric modification compensates for the inherent non-linearity of parallel plate capacitors across temperature ranges while maintaining a relatively simple overall sensor structure.
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 a linear capacitance response to pressure changes, enhancing sensitivity and accuracy by translating small membrane displacements into significant comb-finger capacitor displacements without requiring a reference capacitor, while compensating for acceleration effects.
Implementation Method 1
At least one spring structure is mechanically connected to the at least one projection and the segment, wherein out-of-plane movement of the membrane applies an out-of-plane force to the at least one spring structure which in turns translates the out-of-plane force to an in-plane force applied to the frame
Implementation Method 2
A capacitive sensor associated with the frame for detecting sliding in-plane movement of the frame with respect to the substrate
Data Source
AI summary
A pressure-sensor includes a substrate with a cavity therein and a membrane suspended over the cavity. The cavity is connected to external air pressure so a change in external air pressure causes out-of-plane movement of the membrane. A frame suspended over the membrane includes a segment connected to the membrane but disconnected from other frame portions. A projection extends from the frame. A first spring is connected to the projection, a second spring is connected to the segment, and an end portion connects the springs so out-of-plane movement of the membrane applies out-of-plane force to the second spring, which is transferred to the first spring by the end portion and translated to an in-plane force by the first spring and applied to the projection. This causes lateral sliding movement of the frame with respect to the substrate. A capacitive-sensor detects sliding movement of the frame with respect to the substrate.