MEMS Acceleration Sensor Thickness-Direction Sensitivity
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Solution Overview
Problem
Existing capacitive MEMS acceleration sensors face limitations in sensitivity and signal-to-noise ratio when detecting acceleration along the thickness direction, as they rely on variable inter-electrode area or distance, which either increases capacitance sensitivity at the cost of noise or vice versa.
Innovation Solution
The acceleration sensor employs a substrate with a first mass portion supported by a beam portion, where the beam portion includes a second mass portion with reduced mass and a spring portion with a lower spring constant, allowing the movable and fixed electrodes to face each other perpendicularly, thereby enhancing sensitivity by varying the inter-electrode distance in response to acceleration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If variable inter-electrode area method is used to detect acceleration, then sensitivity is improved, but noise increases
Solution Approach 1:
The patent changes the detection parameter from inter-electrode area variation to inter-electrode distance variation. By making the electrodes face each other in the thickness direction with a small initial distance, the capacitance sensitivity becomes inversely proportional to the square of the distance, dramatically improving sensitivity while maintaining low noise levels.
Solution Approach 2:
The patent transitions from planar electrode arrangement (area variation) to thickness direction arrangement (distance variation). This dimensional change allows the movable electrode to approach the fixed electrode vertically, creating a capacitive structure where sensitivity depends on distance rather than area, thereby resolving the sensitivity-noise tradeoff.
2Measurement precision
If variable inter-electrode distance method is used to detect acceleration, then sensitivity is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent introduces a counterweight portion on the movable electrode that balances the mass distribution. This counterweight compensates for the effect of gravity and reduces the influence of parasitic capacitances, allowing the sensor to achieve high sensitivity without requiring extremely tight manufacturing tolerances for electrode alignment.
Solution Approach 2:
The electrode structure is segmented into multiple components: a fixed electrode on the substrate, a movable electrode on the movable portion, and a counterweight portion. This segmentation allows independent optimization of each component's function and simplifies the manufacturing process by enabling separate fabrication and assembly of critical elements.
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 configuration improves sensitivity and signal-to-noise ratio by increasing capacitance sensitivity in inverse proportion to the square of the distance between electrodes, allowing for more accurate detection of acceleration along the thickness direction.
Implementation Method 1
acceleration along a thickness direction is detected by detecting a capacitance between a movable electrode and a fixed electrode that face each other along a direction perpendicular to a thickness direction of the substrate
Data Source
AI summary
The present disclosure provides an acceleration sensor. The acceleration sensor includes: a substrate; a first mass portion supported by the substrate so as to be movable along a thickness direction of the substrate; and a beam portion supporting the first mass portion on the substrate. The beam portion includes: a second mass portion having a mass less than a mass of the first mass portion; a first spring portion connecting the first mass portion with the second mass portion; and a second spring portion having a spring constant smaller than a spring constant of the first spring portion and connecting the second mass portion with the substrate. A movable electrode of a sensor element is disposed on the second mass portion and configured to detect an acceleration along the thickness direction of the substrate. A fixed electrode of the sensor element is disposed on the substrate.