Offset Rejection Electrodes in MEMS Sensors
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Solution Overview
Problem
Microelectromechanical system (MEMS) sensors face undesirable forces during fabrication and operation, leading to deviations in parallel alignment between the MEMS device and the sensing reference plane, causing non-ideal conditions such as tilting and curvature, which affect the accuracy of motion detection.
Innovation Solution
A MEMS sensor system with a sensing reference plane and a pattern of sensing elements, including alternating positive and negative electrodes, that share axes of polarity anti-symmetry, coupled with a signal processing circuit to combine the signals and reject offset caused by deviations, ensuring accurate motion detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sensing elements are used in MEMS sensors, then the device can detect motion, but offset errors occur due to deviations in parallel alignment between the MEMS device and sensing reference plane
Solution Approach 1:
The sensing element is divided into multiple segments arranged in a specific pattern around the proof mass. Each segment independently senses the gap to the proof mass, and their signals are combined to reject offset errors caused by misalignment, while maintaining motion detection capability.
Solution Approach 2:
The sensing elements are positioned asymmetrically relative to the proof mass in a non-uniform pattern. This asymmetric arrangement, combined with specific signal weighting, enables the system to reject offset errors from parallel alignment deviations while preserving sensitivity to actual motion.
2Reliability
If the MEMS sensor uses a simple sensing element arrangement, then the device complexity is low, but it cannot reject offset errors from fabrication and packaging deviations
Solution Approach 1:
The sensing element is segmented into multiple parts arranged in a specific geometric pattern. This segmentation enables offset rejection through differential measurement while keeping each individual segment simple in structure.
Solution Approach 2:
Multiple sensing elements are merged into a unified sensing system with coordinated signal processing. The combined output of all segments provides offset rejection capability while maintaining relatively simple individual element structures.
3Measurement precision
If the sensing elements are positioned to maximize motion detection sensitivity, then the measurement precision improves, but the parallel alignment deviation causes larger offset errors
Solution Approach 1:
The sensing element is divided into multiple segments positioned at different locations around the proof mass. This segmentation allows the system to maintain high motion detection sensitivity while compensating for parallel alignment deviations through differential measurement of multiple gaps.
Solution Approach 2:
Each sensing segment is positioned to optimize local gap sensing, with varying distances and orientations relative to the proof mass. This local optimization, when combined across all segments, provides both high sensitivity and robustness to alignment variations.
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 system effectively reduces offset errors by using a differential sensing scheme that detects motion only when the gap between electrodes changes due to movement, providing a zero or reduced offset output even under non-ideal conditions.
Implementation Method 1
a pattern of sensing elements coupled between the sensing reference plane and the at least one proof mass to detect motion normal to the sensing reference plane
Data Source
AI summary
A MEMS sensor that comprises a sensing reference plane, at least one anchor coupled to the sensing reference plane, wherein the sensing reference plane is divided by a first and a second axis forming four quadrants on the sensing reference plane, at least one proof mass coupled to the at least one anchor, wherein one of the at least one proof mass moves under an external excitation, and a pattern of sensing elements on the sensing reference plane to detect motion normal of the at least one proof mass relative to the sensing reference plane, wherein the pattern of sensing elements comprises at least three sensing elements in each of the four quadrants.