Segmented MEMS Pressure Sensor for Hermeticity and Sensitivity Trade-off
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Solution Overview
Problem
MEMS pressure sensors face issues with insensitivity, inaccuracy, and signal drift due to variations in membrane thickness, diameter, and stress, which affect their performance and accuracy, especially in harsh environments or over time, and require internal calibration to ensure consistent operation.
Innovation Solution
The use of a MEMS pressure sensor design with vertical connections from a top metal layer of an IC, featuring segmented electrodes that allow differential capacitance measurement and voltage biasing to maintain a fixed ratio between inner and outer electrodes, enabling self-calibration and improved sensitivity, linearity, and dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the membrane thickness is reduced to increase deflection and sensitivity, then sensitivity is improved, but hermeticity deteriorates
Solution Approach 1:
The membrane is segmented into multiple regions with different thicknesses: a thinner central region for high deflection and sensitivity, and thicker peripheral regions for hermetic sealing. This segmentation allows simultaneous optimization of sensitivity (through thin central membrane) and hermeticity (through thick peripheral membrane).
Solution Approach 2:
Different regions of the membrane have different thickness properties tailored to their specific functions: the central region has reduced thickness to maximize deflection for pressure sensing, while the peripheral regions maintain greater thickness to ensure hermetic sealing and structural integrity.
2Manufacturing precision
If process variations are reduced to improve manufacturing uniformity, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The device includes self-calibration functionality that automatically compensates for manufacturing variations. The sensor performs internal calibration routines using its own structure, eliminating the need for external calibration equipment and reducing the impact of process variations on final performance.
Solution Approach 2:
The patent implements feedback mechanisms where the sensor measures its own performance characteristics and adjusts accordingly. This feedback loop compensates for manufacturing variations in membrane thickness and other parameters, maintaining consistent performance across devices produced with standard process variations.
3Reliability
If the reference cavity pressure is stabilized to reduce signal drift, then reliability is improved, but device complexity increases
Solution Approach 1:
The sealing structure is segmented into multiple layers and regions, allowing different portions to handle different aspects of the sealing challenge. This multi-layer approach provides enhanced hermeticity without requiring a single complex sealing mechanism.
Solution Approach 2:
The patent employs composite material structures for the membrane and sealing layers, combining materials with different properties to achieve both hermeticity and mechanical flexibility. The composite structure maintains stable reference cavity pressure while accommodating thermal and mechanical variations.
4Measurement precision
If the membrane area is increased to improve sensitivity, then measurement precision is improved, but device size increases
Solution Approach 1:
The patent transitions from a single-plane membrane structure to a three-dimensional structure with varying thickness through the depth dimension. This allows the membrane to have large effective sensing area while maintaining compact overall device footprint by utilizing vertical space for the thicker peripheral sealing regions.
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 enhances the sensitivity, accuracy, and reliability of MEMS pressure sensors by allowing for internal calibration and compensation of device variations, improving signal-to-noise ratio and dynamic range, and enabling autonomous recalibration to maintain precise pressure measurements.
Implementation Method 1
MEMS pressure sensors are well known, and typically have a piezoresistive or a capacitive read-out, to detect movement of a suspended structure when it is subjected to an external pressure
Implementation Method 2
The external pressure is measured because the pressure difference between the external pressure and the gauge pressure generates a force on the membrane, which causes the membrane to deflect
Data Source
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AI summary
A MEMS pressure sensor wherein at least one of the electrode arrangements comprises an inner electrode and an outer electrode arranged around the inner electrode. The sensor is provided over an integrated circuit. The capacitances associated with the inner electrode and the outer electrode can be independently measured and can be differentially measured. This arrangement enables various different read out schemes to be implemented and also enables improved compensation for variations between devices or changes in device characteristics over time.