Capacitive MEMS Sensor with Flexural Suspension Arrays
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Solution Overview
Problem
Capacitive Micro Electro-Mechanical Systems (MEMS) for position and acceleration sensing face limitations in sensitivity and accuracy due to unwanted movement of compliant components and a restricted dynamic range in signal conversion.
Innovation Solution
A sensor design featuring high aspect ratio flexural suspension elements and electrode arrays with specific pitch ratios, allowing controlled movement of a proof mass relative to electrode arrays, enabling accurate capacitive sensing by maintaining a uniform gap and adjusting electrical null positions for enhanced dynamic range and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If compliant components are used in capacitive MEMS sensing, then the sensor can detect position and acceleration, but sensitivity and accuracy are reduced due to unwanted movement of these components
Solution Approach 1:
The sensor is divided into three separate wafers (first wafer with electrode array, second wafer with proof mass and electrode array, third wafer cap), allowing independent optimization of each component. The proof mass is suspended by flexural suspension elements that separate the sensing function from the support structure, reducing unwanted movements and improving measurement precision while maintaining reliability.
Solution Approach 2:
The patent replaces traditional mechanical lever systems with capacitive sensing. Instead of using mechanical amplification mechanisms that introduce friction and wear, the invention uses electrical field-based capacitive measurements between electrode arrays to detect position and acceleration, eliminating mechanical errors and improving both accuracy and stability.
2Measurement precision
If traditional capacitance-to-position conversion methods are used, then position can be measured, but the dynamic range is limited
Solution Approach 1:
The patent transitions from single-point capacitive sensing to array-based distributed capacitive sensing. By using multiple electrodes arranged in arrays on both the fixed wafer and proof mass wafer, the system measures capacitance across multiple spatial dimensions simultaneously. This array approach enables determination of both position and acceleration while expanding the measurable dynamic range beyond what single-point sensing can achieve.
Solution Approach 2:
The invention changes the sensing parameter from simple capacitance magnitude to capacitance gradient and curvature across the electrode arrays. By measuring how capacitance varies across different electrode positions and using higher-order spatial derivatives, the system can distinguish between position and acceleration effects, thereby expanding the dynamic range and measurement versatility.
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
Improves sensitivity and accuracy of position and acceleration sensing, expanding the dynamic range from approximately 140 dB to 200 dB and achieving position resolution below 10 fm and acceleration resolution below 1 nG.
Implementation Method 1
a first electrode array disposed on the proof mass and a second electrode array disposed on a planar surface of a support structure... generate an output signal based upon a phase-to-phase cross capacitance between the first electrode array and the second electrode array
Implementation Method 2
high aspect ratio flexural suspension elements... allowing controlled movement of a proof mass relative to electrode arrays
Data Source
AI summary
Various systems and methods for sensing are provided. In one embodiment, a sensing system is provided that includes a first electrode array disposed on a proof mass, and a second electrode array disposed on a planar surface of a support structure. The proof mass is attached to the support structure via a compliant coupling such that the first electrode array is positioned substantially parallel to and faces the second electrode array and the proof mass is capable of displacement relative to the support structure. The first electrode array includes a plurality of first patterns of electrodes and the second electrode array includes a plurality of second patterns of electrodes. The sensing system further includes circuitry configured to provide an input voltage to each of the second patterns of electrodes to produce an electrical null position for the first electrode array.