MEMS Capacitive Sensing Layout for Linear Displacement Output
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Solution Overview
Problem
Parallel plate capacitors in MEMS devices exhibit nonlinearity in capacitance change with displacement, leading to reduced detection accuracy.
Innovation Solution
Incorporating a reference capacitor into the MEMS device, coupled with a detection circuit and a divider, to eliminate nonlinearity by performing differential detection and signal division.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a parallel plate capacitor is used for detection, then the device is easy to fabricate and has high sensitivity, but the capacitance change is nonlinear with displacement, reducing detection accuracy
Solution Approach 1:
The single capacitor is segmented into four capacitors (first, second, third, and fourth capacitors) arranged in a specific configuration. The movable electrode plate is divided into multiple parts, each forming a capacitor with corresponding fixed electrode plates. This segmentation transforms the nonlinear single-capacitor detection into a system where differential measurement of multiple capacitors eliminates nonlinearity, thereby improving detection accuracy while maintaining ease of fabrication through standard MEMS processes.
Solution Approach 2:
A differential detection circuit is introduced as an intermediary between the capacitors and the output. This circuit processes the capacitance changes from the four capacitors through differential measurement, converting the nonlinear capacitance-displacement relationship into a linear output signal. The intermediary circuit effectively decouples the simple capacitor structure from the linear detection requirement, resolving the contradiction between ease of manufacture and measurement precision.
2Adaptability or versatility
If the displacement between parallel plates increases, then the detection range is improved, but the nonlinearity increases, seriously affecting detection accuracy
Solution Approach 1:
The detection system is segmented into four capacitors with the movable electrode plate positioned between fixed electrode plates on both sides. This configuration allows the movable plate to displace in either direction while maintaining capacitance changes in all four capacitors. The segmentation enables the system to handle larger displacement ranges while the differential detection circuit compensates for nonlinearity, thus expanding detection range without sacrificing accuracy.
Solution Approach 2:
The movable electrode plate is positioned asymmetrically between the fixed electrode plates, allowing it to move in both positive and negative directions relative to the nominal position. This asymmetric arrangement enables bidirectional detection with extended range. The differential detection circuit processes the asymmetric capacitance changes to produce a linear output, resolving the contradiction between extended detection range and maintained accuracy.
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
The solution achieves linear output voltage with respect to displacement, enhancing detection accuracy by theoretically eliminating nonlinearity and reducing temperature drift.
Implementation Method 1
a first capacitor is formed by the first electrode plate and the movable electrode plate, and a second capacitor is formed by the second electrode plate and the movable electrode plate
Implementation Method 2
a third capacitor is formed by the third electrode plate and the movable electrode plate, and a fourth capacitor is formed by the fourth electrode plate and the movable electrode plate
Data Source
AI summary
Disclosed is a MEMS device, comprising: a movable electrode plate; a first electrode plate and a third electrode plate on a first side of the movable electrode plate; a second electrode plate and a fourth electrode plate on a second side of the movable electrode plate. The first electrode plate, the second electrode plate, the third electrode plate and the fourth electrode plate respectively form a first capacitor, a second capacitor, a third capacitor, a fourth capacitor with the movable electrode plate, the first capacitor and the second capacitor are connected to a detection circuit, the third capacitor and the fourth capacitor are connected to a reference circuit, an output of the detection circuit and an output of the reference circuit are connected to an input of a divider for eliminating nonlinear relationship between the output voltage of the detection circuit and the displacement of the movable electrode plate.