MEMS Accelerometer Deformation Mapping for Offset Calibration
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Solution Overview
Problem
MEMS sensors, particularly out-of-plane accelerometers, face challenges in maintaining sensitivity and offset stability due to size reductions and substrate deformation, leading to inaccurate measurements.
Innovation Solution
The use of multiple sense electrodes positioned on the substrate layer to determine and compensate for deformation patterns, with processing circuitry multiplexing signals from these electrodes to improve sensitivity and stability, and the integration of tilt sense electrodes to account for MEMS layer tilt and offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple sense electrodes are added to determine substrate deformation, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The sensor is divided into multiple independent sense electrodes (first plurality and second plurality) positioned at different locations beneath the proof mass. Each electrode independently measures capacitance changes, and the processing circuitry segments the measurement process into parallel operations, enabling simultaneous detection of substrate deformation at multiple points without requiring a single complex sensor structure.
Solution Approach 2:
The substrate layer itself serves as an intermediary element that transmits deformation information to the sense electrodes. By positioning electrodes on the substrate layer, the system uses the substrate as a mediator to indirectly measure proof mass displacement and substrate deformation, converting mechanical deformation into electrical signals through capacitance changes without direct mechanical coupling.
2Measurement precision
If sense electrodes are positioned on the substrate layer, then sensitivity is improved, but manufacturing precision requirements increase
Solution Approach 1:
The sense electrodes are pre-positioned on the substrate layer during substrate fabrication, before the MEMS layer is deposited. This preliminary placement allows the electrodes to be integrated into the substrate structure itself, establishing their positions in advance and reducing the need for subsequent precision alignment operations while ensuring optimal sensitivity configuration.
Solution Approach 2:
The system uses multiple sense electrodes as copies or replicas of the proof mass position detection mechanism. Instead of relying on a single electrode that would require precise positioning, multiple electrodes provide redundant measurement points, allowing the system to infer substrate deformation patterns through comparative analysis of capacitance changes across different electrode locations.
3Device complexity
If signal multiplexing is implemented, then device complexity is reduced, but measurement precision may be compromised
Solution Approach 1:
Multiple capacitance signals from different sense electrodes are merged and processed simultaneously by the processing circuitry. The circuitry combines the signals from the first and second plurality of electrodes into a unified processing stream, enabling parallel analysis of deformation patterns while maintaining measurement precision through coordinated signal processing rather than sequential operations.
Solution Approach 2:
The processing circuitry performs multiple functions using a single integrated system: it processes signals from multiple electrodes, determines substrate deformation patterns, calculates proof mass displacement, and compensates for sensor misalignment. This multi-functional approach consolidates what would otherwise require separate processing stages into a single circuitry block, reducing overall device complexity while maintaining measurement accuracy through comprehensive data analysis.
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 approach enhances the stability and sensitivity of MEMS sensors by accurately determining substrate deformation and compensating for errors, leading to improved measurement accuracy and reduced thickness in consumer devices.
Implementation Method 1
movement of the proof masses in response to the forces. In some implementations, this 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 system (MEMS) accelerometer incorporates deformation sensing with a plurality of sense electrodes positioned to facilitate determining a deformation pattern (e.g., asymmetric or symmetric) of an underlying substrate layer relative to a MEMS layer. The deformation pattern of the substrate layer contributes to offset and/or sensitivity of the accelerometer, so the determination of the deformation pattern enables processing circuitry to compensate and improve offset and/or sensitivity stability. Tilt sense electrodes and/or comparison electrodes may be incorporated alongside the plurality of sense electrodes to monitor deformation of the substrate layer relative to a fixed portion of the MEMS layer.