MEMS Accelerometer Electrode Symmetry for Package Stress Compensation
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Solution Overview
Problem
MEMS accelerometers face accuracy issues due to package stress caused by deformation from processing, ambient temperature, and overmold pressure, which are not effectively mitigated by traditional electrode designs that prioritize high acceleration accuracy by locating electrodes distal from the proof mass anchor.
Innovation Solution
The implementation of enhanced differential electrode structures with symmetric arrangements close to the proof mass anchor, utilizing comb-like structures that interleave and bisect the anchor, to cancel out package stress-induced anomalies and provide accurate acceleration measurements across multiple axes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrodes are located distal from the proof mass anchor to prioritize high acceleration accuracy, then acceleration measurement precision is improved, but package stress effects increase and degrade reliability
Solution Approach 1:
The patent employs asymmetric electrode positioning relative to the proof mass anchor, where electrodes are deliberately placed at non-uniform distances and angles from the anchor point. This asymmetric arrangement creates differential stress distribution that compensates for package stress effects, allowing the accelerometer to maintain high measurement precision while becoming more resistant to package-induced deformations.
2Reliability
If electrodes are located close to the proof mass anchor to reduce package stress effects, then reliability is improved, but acceleration measurement precision deteriorates
Solution Approach 1:
The patent implements local quality by creating non-uniform electrode distributions where specific electrode pairs are positioned at different locations relative to the anchor. This localized variation in electrode geometry and positioning allows different regions of the proof mass to experience different stress conditions, enabling the system to compensate for package stress while maintaining measurement accuracy through differential measurements.
3Ease of manufacture
If symmetric electrode structures are used to simplify manufacturing, then ease of manufacture is improved, but ability to cancel package stress effects deteriorates
Solution Approach 1:
The patent deliberately introduces asymmetric elements into the electrode structure, where corresponding electrodes are positioned at different distances and orientations from the anchor. This asymmetry is intentionally designed to create differential responses to package stress, enabling stress cancellation through signal processing while maintaining manufacturing feasibility through standard fabrication processes.
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 effectively cancels out package stress effects, enhancing the robustness and accuracy of MEMS accelerometers by distributing stress evenly across the anchor, thereby improving measurement precision and reliability.
Implementation Method 1
the first electrode and the second electrode are configured to provide a differential signal representative of acceleration of the accelerometer along an axis perpendicular to the first plane
Data Source
AI summary
Techniques for compensating package stress of a proof mass are provided. In an example, a proof mass can be suspended from a substrate by a proof mass anchor. The first proof mass can have a major surface that defines a first plane. Portions of electrodes forming part of the proof mass can be symmetric with each other across a first line, wherein the first line bisects the first proof mass anchor, extends parallel to the first plane and extends between the first electrode and the second electrode.