MEMS Proof Mass Offset Compensation via Segmented Capacitive Sensing
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Solution Overview
Problem
Microelectromechanical (MEMS) sensors face challenges in accurately measuring external forces such as linear acceleration and angular velocity due to external stresses caused by manufacturing tolerances, assembly stresses, and environmental changes, which can lead to misalignment and offset errors in the sensor's measurement parameters.
Innovation Solution
The MEMS sensor design incorporates two proof masses, one that moves in response to the desired external force and another that remains stationary to compensate for undesired forces, using capacitive sensing to determine the accurate measurement value by processing signals from both proof masses and electrodes, thereby mitigating the effects of external stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single proof mass is used for sensing, then the device structure is simple, but measurement precision deteriorates due to offset errors from external stresses
Solution Approach 1:
The sensor is segmented into two functionally distinct proof masses: a first proof mass that responds to external forces for measurement, and a second proof mass that remains stationary to sense offset errors. This segmentation allows independent optimization of each component's function, resolving the contradiction between structural simplicity and measurement precision.
Solution Approach 2:
The second proof mass acts as an intermediary element that indirectly measures offset errors caused by external stresses. By coupling this stationary proof mass to the same electrode structure, the system can detect and compensate for misalignment without requiring direct measurement of the offset source, thus improving precision while maintaining structural simplicity.
2Device complexity
If proof masses are made electrically coupled, then the sensing mechanism is simpler, but reliability deteriorates due to interference between proof masses
Solution Approach 1:
The electrical system is segmented into separate circuits for the first and second proof masses. The first proof mass uses a first sense element connected to a first electrode, while the second proof mass uses a second sense element connected to a second electrode. This electrical segmentation prevents interference between the proof masses while maintaining reliable and independent measurement channels.
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 design enhances the accuracy of MEMS sensors by effectively compensating for external stresses, ensuring precise measurement of linear acceleration and angular velocity despite misalignment and offset issues, resulting in improved reliability and performance across various applications.
Implementation Method 1
the movement is measured based on distance between the movable proof masses and fixed electrodes, which form capacitors for sensing the movement
Data Source
AI summary
A microelectromechanical (MEMS) sensor comprises MEMS components located within a MEMS layer and located relative to one or more electrodes. A plurality of proof masses are located within the MEMS layer and are not electrically coupled to each other within the MEMS layer. Both the first proof mass and the second proof mass move relative to at least a common electrode of the one or more electrodes, such that the relative position of each of the proof masses relative to the electrode may be sensed. A sensed parameter may be determined based on the sensed relative positions.