MEMS Differential Vertical Sense Electrodes
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Solution Overview
Problem
MEMS devices with traditional teeter-totter style vertical sensing are sensitive to substrate curvature and harsh accelerations, leading to inaccurate signal readings due to common mode displacement and frequency tuning issues.
Innovation Solution
The implementation of MEMS devices with two structural layers where a movable sense mass is interleaved below one fixed electrode and above a separate fixed electrode, allowing differential sensing to cancel out common mode displacement signals, and reducing sensitivity to substrate curvature and accelerations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional teeter-totter style vertical sensing is used, then the device structure is simple, but the device is sensitive to substrate curvature and harsh accelerations leading to inaccurate signal readings
Solution Approach 1:
The sensing system is segmented into multiple independent capacitive sensing elements arranged in a differential configuration. Instead of a single teeter-totter style sensor, the patent uses multiple sense masses and corresponding electrodes that can be independently positioned and weighted to compensate for substrate curvature and acceleration effects.
Solution Approach 2:
The patent introduces dummy sense masses and corresponding capacitive elements as intermediary components that do not provide primary sensing but serve to balance and cancel out common-mode signals caused by substrate curvature and accelerations, thereby isolating the differential signal from harmful environmental factors.
2Reliability
If traditional vertical sensing is used, then the device occupies less space, but common mode displacement and frequency tuning issues arise
Solution Approach 1:
The patent merges multiple sensing functions into a single integrated capacitive sensing system. The differential capacitive elements and dummy elements are combined in a unified structure that simultaneously provides common-mode rejection and differential sensing, reducing the need for separate compensation mechanisms.
Solution Approach 2:
The capacitive sensing elements serve multiple functions: primary differential sensing, common-mode signal cancellation, and frequency tuning. The same structural components that form the sensing capacitors also provide the necessary electrical connections and mechanical support, reducing overall device complexity.
3Measurement precision
If differential sensing with multiple layers is implemented, then common mode displacement is canceled, but the device complexity increases
Solution Approach 1:
The patent implements a nested layer structure where second structural layers containing sense masses and electrodes are positioned within or between first structural layers. This nesting approach allows multiple differential sensing elements to be stacked vertically, achieving common-mode rejection while maintaining a compact footprint and reducing lateral space requirements.
Solution Approach 2:
The patent transitions from lateral arrangement of sensing elements to vertical stacking in the Z-dimension. By arranging sense masses and electrodes in multiple structural layers separated by gaps in the vertical direction, the patent achieves differential sensing and common-mode rejection without increasing the device's planar footprint, effectively using the third dimension to resolve the complexity trade-off.
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 provides a robust and space-efficient solution for MEMS sensors, reducing the impact of substrate curvature and harsh accelerations on signal accuracy and maintaining sensitivity, effectively canceling out common mode displacement and frequency tuning issues.
Implementation Method 1
Capacitive-sensing MEMS sensor designs are highly desirable for operation in high gravity environments and in miniaturized devices
Data Source
AI summary
A MEMS device includes a first sense electrode and a first portion of a sense mass formed in a first structural layer, where the first sense electrode is fixedly coupled with the substrate and the first portion of the sense mass is suspended over the substrate. The MEMS device further includes a second sense electrode and a second portion of the sense mass formed in a second structural layer. The second sense electrode is spaced apart from the first portion of the sense mass in a direction perpendicular to a surface of the substrate, and the second portion of the sense mass is spaced apart from the first sense electrode in the same direction. A junction is formed between the first and second portions of the sense mass so that they are coupled together and move concurrently in response to an imposed force.