MEMS Pressure Sensor Electrode Segmentation for Noise Reduction
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Solution Overview
Problem
Conventional air pressure sensors for mobile devices suffer from measurement errors due to noise in single capacitor designs, which limits their accuracy in detecting altitude changes, especially in high-altitude environments where absolute and relative pressure measurements are critical for navigation systems.
Innovation Solution
A MEMS device with multiple electrodes is developed, featuring a sensing capacitor and a reference capacitor, where the second electrode has a sensing portion and a stationary portion, maintaining a constant distance between the stationary portion and the third electrode, reducing noise and enhancing measurement accuracy by using a silicon-on-insulator (SOI) wafer and wafer-to-wafer bonding process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single capacitor is used in the pressure sensor, then the device structure is simple, but measurement precision deteriorates due to noise
Solution Approach 1:
The second electrode is segmented into two distinct portions: a sensing portion that moves with pressure changes and a stationary portion that remains fixed. This segmentation allows the sensing portion to form a variable capacitor with the first electrode while the stationary portion forms a reference capacitor with the third electrode, enabling noise reduction through differential measurement without complicating the overall device structure
Solution Approach 2:
The stationary portion of the second electrode creates a reference capacitor that copies the structural configuration of the sensing capacitor but remains stationary. This reference capacitor serves as a stable baseline for comparison, allowing the system to distinguish between actual pressure-induced changes and noise by comparing the variable and reference capacitor values
2Measurement precision
If a differential pressure sensor with reference capacitor is designed, then measurement precision improves, but device complexity increases
Solution Approach 1:
The sensing and reference capacitors are merged into a single integrated structure where the second electrode serves dual purposes through its two portions. The sensing portion forms the variable capacitor with the first electrode, while the stationary portion forms the reference capacitor with the third electrode. This merging approach achieves differential measurement functionality without requiring completely separate capacitor structures, thus reducing overall device complexity
3Measurement precision
If the hermetic space is made vacuum for absolute pressure detection, then measurement precision improves, but device complexity increases due to hermetic sealing requirements
Solution Approach 1:
The patent applies different quality characteristics to different portions of the hermetic space. The region containing the sensing capacitor (first hermetic space) is maintained as vacuum for absolute pressure measurement, while the region containing the reference capacitor (second hermetic space) can have different pressure conditions. This local differentiation allows absolute pressure detection functionality without requiring the entire device structure to meet stringent hermetic sealing requirements
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 MEMS device with multiple electrodes improves the accuracy of air pressure measurements by minimizing noise and allowing for miniaturization, making it suitable for use in mobile electronics, such as smartphones and navigation systems, while maintaining a constant reference capacitance for precise altitude detection.
Implementation Method 1
The deformation will change the capacitance between the diaphragm 4-1 and the stationary electrode 3 due to a change in the distance therebetween
Implementation Method 2
When such a sensor is placed in an environment where an external air pressure P exists relative to the cover 4, the diaphragm 4-1 will deform
Implementation Method 3
the stationary portion 403 is configured for forming the reference capacitor 140
Data Source
AI summary
A MEMS device with a first electrode, a second electrode and a third electrode is disclosed. These electrodes are disposed on a substrate in such a manner that (1) a pointing direction of the first electrode is in parallel with a normal direction of the substrate, (2) a pointing direction of the third electrode is perpendicular to the pointing direction of the first electrode, (3) the second electrode includes a sensing portion and a stationary portion, (4) the first electrode and the sensing portion are configured to define a sensing capacitor, and (5) the third electrode and the stationary portion are configured to define a reference capacitor. This arrangement facilitates the MEMS device such as a differential pressure sensor, differential barometer, differential microphone and decoupling capacitor to be miniaturized.