MEMS Accelerometer Electrode Thickness Asymmetry
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Solution Overview
Problem
Existing acceleration sensors using silicon micro electro mechanical systems (MEMS) face challenges in distinguishing between positive and negative directions due to equal capacitance changes when the thickness of movable and fixed electrodes are the same, leading to reduced detection accuracy and increased sensitivity of other axes due to torsion or distortion caused by weight imbalance.
Innovation Solution
A physical quantity sensor design with a movable electrode portion and a fixed electrode portion, where the thickness of movable electrodes in different groups is varied, and arranged symmetrically to distinguish between directions, combined with a controller for differential signal processing to enhance detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the thickness of movable electrode and fixed electrode are made the same, then the manufacturing process is simplified, but the sensor cannot distinguish between positive and negative directions at the detection axis
Solution Approach 1:
The patent applies asymmetry by making the thickness of movable electrodes different between the first and second directions. Specifically, the movable electrodes in the first direction have a first thickness, while the movable electrodes in the second direction have a second thickness that is different from the first thickness. This asymmetric thickness design enables the sensor to distinguish between positive and negative acceleration directions by creating different capacitance change characteristics for opposite directions, thereby resolving the direction discrimination problem while maintaining manufacturing feasibility.
Solution Approach 2:
The patent implements local quality by varying the thickness of movable electrodes based on their specific position and function. Different regions of the movable electrode structure have different thicknesses optimized for their particular detection needs. The first movable electrodes have one thickness configuration optimized for detecting acceleration in the first direction, while the second movable electrodes have a different thickness configuration optimized for the second direction, allowing each local region to contribute optimally to direction discrimination.
2Measurement precision
If the thickness of movable electrodes is reduced to enable direction discrimination, then direction detection is improved, but detection accuracy is lowered due to torsion or distortion caused by loss of weight balance
Solution Approach 1:
The patent applies the counterweight principle by strategically positioning and dimensioning the movable electrodes to balance the weight distribution of the movable body. The asymmetric thickness design is compensated by the symmetric arrangement of electrode groups, where the first and second movable electrode groups are positioned to create a balanced weight distribution around the detection axis. This prevents torsion and distortion during acceleration detection, maintaining reliability while enabling direction discrimination through the thickness variation.
Solution Approach 2:
The patent uses asymmetry in electrode thickness combined with symmetric positioning to resolve the contradiction. The movable electrodes have asymmetric thicknesses (first thickness in one direction, second thickness in another direction) to enable direction discrimination, but they are arranged symmetrically in pairs (first and second movable electrode groups) to maintain weight balance. This combination allows the sensor to distinguish directions through capacitance differences while preventing unwanted torsion and distortion.
3Measurement precision
If asymmetric thickness design is implemented to distinguish directions, then direction discrimination is enabled, but the sensitivity of other axes increases due to weight imbalance
Solution Approach 1:
The patent implements asymmetric thickness design where movable electrodes in the first direction have a first thickness and movable electrodes in the second direction have a second thickness. This asymmetry enables direction discrimination by creating distinct capacitance change patterns for different acceleration directions. The asymmetric thickness is carefully designed to provide sufficient directional discrimination capability while minimizing the impact on other axis sensitivity.
Solution Approach 2:
The patent compensates for the weight imbalance caused by asymmetric electrode thickness through strategic positioning and pairing of electrode groups. The first and second movable electrode groups are arranged symmetrically with respect to the detection axis, creating a counterbalancing effect that minimizes torsion and reduces sensitivity to accelerations in directions other than the intended detection axis. This maintains measurement specificity while enabling direction discrimination.
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 sensor achieves improved direction discrimination and reduced sensitivity of other axes, maintaining high detection accuracy by balancing weight and using differential signal processing.
Implementation Method 1
acceleration in a Z axis direction, for example, is measured based on a change in static capacitance between rotor measurement plates and stator measurement plates at that time
Data Source
AI summary
According to a physical quantity sensor, a first movable electrode group, a second movable electrode group, a third movable electrode group, and a fourth movable electrode group are arranged in this order along a first direction. In a third direction, a thickness of a second movable electrode in the second movable electrode group and a thickness of a third movable electrode in the third movable electrode group are different from a thickness of a first movable electrode in the first movable electrode group and a thickness of a fourth movable electrode in the fourth movable electrode group. When an imaginary line extending in a second direction from a center of a fixed portion is an axis of symmetry, the first movable electrode is disposed line-symmetrically with the fourth movable electrode, and the second movable electrode is disposed line-symmetrically with the third movable electrode.