Acceleration Sensor Electrode Angles for Cross-Axis Sensitivity
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Solution Overview
Problem
Acceleration sensors face reduced detection accuracy due to cross-axis sensitivity when detecting acceleration in orthogonal directions, as the displacement of one movable electrode affects the capacitance between other electrodes, leading to interference and inaccurate readings.
Innovation Solution
The acceleration sensor is designed with first- and second-direction movable electrodes and fixed electrodes, where the angles and intervals between these electrodes are optimized to minimize cross-axis sensitivity by forming specific angles with the detection axes, ensuring that changes in capacitance accurately reflect applied accelerations in respective directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If first-direction and second-direction movable electrodes are provided on a common support member to detect acceleration in two orthogonal directions, then the acceleration sensor can detect acceleration in both directions, but cross-axis sensitivity occurs causing reduction in detection accuracy
Solution Approach 1:
The electrode system is segmented into four distinct capacitance detection units: first capacitance (first-direction movable electrode and first-direction fixed electrode), second capacitance (second-direction movable electrode and second-direction fixed electrode), third capacitance (first-direction movable electrode and second-direction fixed electrode), and fourth capacitance (second-direction movable electrode and first-direction fixed electrode). This segmentation allows independent detection of acceleration in orthogonal directions while compensating for cross-axis sensitivity through differential measurement.
Solution Approach 2:
The patent implements a feedback mechanism where the output signals from all four capacitance detection units are processed to compensate for cross-axis sensitivity. The detection unit uses the capacitance values from all four measurements to calculate corrected acceleration values in both orthogonal directions, effectively eliminating the cross-axis interference through computational feedback.
2Measurement precision
If the interval between movable electrode and fixed electrode is reduced to increase capacitance sensitivity, then detection sensitivity improves, but the electrodes may come into contact reducing reliability
Solution Approach 1:
The patent optimizes the geometric parameters of the electrode structure, specifically setting the interval between movable and fixed electrodes to 0.5 μm to 2 μm. This parameter optimization achieves high capacitance sensitivity while preventing electrode contact. Additionally, the electrodes are designed with finite width and appropriate spacing to maintain electrical isolation while maximizing capacitive coupling for sensitive detection.
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 effectively reduces the influence of cross-axis sensitivity, thereby maintaining high detection accuracy for accelerations in both orthogonal directions by ensuring that changes in electrode positions and capacitances accurately correspond to applied forces.
Implementation Method 1
an interval between the movable electrode and the fixed electrode changes in accordance with the acceleration, and hence the acceleration is detected based on a capacitance between the movable electrode and the fixed electrode
Data Source
AI summary
An acceleration sensor includes: a semiconductor substrate that includes a support substrate and a semiconductor layer; a first-direction movable electrode; a second-direction movable electrode; a first-direction fixed electrode; a second-direction fixed electrode; and a support member. The acceleration sensor is configured to detect acceleration in a first direction in the surface direction of the semiconductor substrate and acceleration in a second direction orthogonal to the first direction and parallel to the surface direction. The first-direction movable electrode and the first-direction fixed electrode are provided such that an angle formed by an extended direction of the first-direction movable electrode and the first-direction fixed electrode and the second direction is sin−1(d/L)[deg], and the second-direction movable electrode and the second-direction fixed electrode are provided such that an angle formed by an extended direction of the second-direction movable electrode and the second-direction fixed electrode and the first direction is sin−1(d/L)[deg].