Differential Capacitive Pressure Sensor Linearity
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Solution Overview
Problem
Micro-Electro-Mechanical-System (MEMS) pressure sensors face challenges in accurately measuring pressure due to non-linear capacitance changes and limited sensitivity, especially with single-ended capacitance measurements and small sensing areas.
Innovation Solution
A differential capacitive output pressure sensor device is designed with patterned electrodes on a pressure sensing diaphragm, providing two capacitors that cancel out non-linear outputs, resulting in a more linear pressure change measurement and increased sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If single-ended capacitance measurement is used, then device complexity is reduced, but measurement precision deteriorates due to non-linear output and limited sensitivity
Solution Approach 1:
The single capacitance measurement is segmented into two separate capacitance measurements (C1 and C2) that are measured differentially. This segmentation allows the non-linear components to cancel out when subtracted, improving measurement precision while maintaining relatively simple device structure
Solution Approach 2:
The measurement parameter is changed from single-ended capacitance change (ΔC) to differential capacitance change (ΔC1 - ΔC2). This parameter transformation converts the non-linear single-ended measurement into a linear differential measurement, significantly improving pressure measurement accuracy
2Area of stationary object
If sensing area is reduced, then device size is minimized, but sensitivity deteriorates due to limited capacitance change
Solution Approach 1:
The sensing area is segmented into two separate sensing regions (first sensing area and second sensing area) with separate fixed electrodes and movable electrodes. This segmentation enables differential measurement that amplifies the effective capacitance change signal, improving sensitivity even with reduced total sensing area
Solution Approach 2:
The capacitance measurement parameter is transformed from single-ended to differential mode, which effectively doubles the sensitivity by measuring the difference between two capacitance changes. This parameter change compensates for the reduced sensing area by enhancing the signal-to-noise ratio
Data Source
AI summary
A differential capacitive output pressure sensor device includes a pressure sensor diaphragm layer comprising a pressure sensing diaphragm portion, a movable electrode on the pressure sensing diaphragm portion, a fixed electrode, and a device layer electrode. The pressure sensor device further includes a device layer including a fixed element connected to the device layer electrode and a movable element connected to the movable electrode. As the pressure changes, the pressure sensing diaphragm portion including the movable electrode and the movable element move. This changes the capacitance between the movable electrode and the fixed element inversely to the change in capacitance between the fixed electrode and the moveable element. Accordingly, a differential capacitive output is provided that has improved linearity with respect to the pressure change and increased sensitivity allowing the change in pressure to be measured readily and accurately.