Suspended Membrane Pressure Sensor Without Reference Cavity
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Solution Overview
Problem
Existing pressure sensors face challenges such as signal drift due to unstable gas pressure in reference cavities, difficulty in making thin hermetic membranes, and temperature dependency, which affect sensitivity and accuracy in measuring pressure changes, especially in MEMS technology used in various applications.
Innovation Solution
An integrated circuit apparatus with a suspended membrane forming a chamber, actuated by an electrical control signal to change volume and detect frequency-based characteristics, using openings to equilibrate pressure and prevent gas flow at high frequencies, allowing for precise pressure measurement without a reference cavity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hermetically sealed membrane is used to seal a reference cavity, then signal drift is reduced, but manufacturing difficulty increases due to the challenge of making thin membranes hermetic
Solution Approach 1:
The patent removes the reference cavity entirely from the sensor design. Instead of sealing a reference cavity with a hermetic membrane, the invention uses a single membrane exposed only to the measurement pressure, eliminating the need for hermetic sealing while maintaining signal stability through differential measurement architecture
Solution Approach 2:
The patent divides the sensing element into multiple independent sensing regions (first and second sensing elements) that can be differentially connected to the output circuit. This segmentation allows differential measurement without requiring a hermetically sealed reference cavity, as each element responds to pressure changes independently
2Measurement precision
If thin membranes are used to increase deflection and sensitivity, then measurement precision improves, but hermetic sealing becomes difficult to achieve
Solution Approach 1:
The reference cavity is extracted from the design, eliminating the hermetic sealing requirement entirely. Thin membranes can now be used for maximum sensitivity without the manufacturing constraint of achieving hermetic seals, as the membrane only needs to sense pressure, not seal a volume
Solution Approach 2:
The membrane is designed with non-uniform thickness, being thinnest at the center for maximum deflection and sensitivity, while having thicker edge portions for mechanical support and anchoring. This local quality variation optimizes both sensitivity and manufacturability without requiring hermetic sealing
3Reliability
If gas pressure in the reference cavity is made stable, then signal drift is reduced, but the system becomes more sensitive to temperature changes according to Boyle's law
Solution Approach 1:
The reference cavity is removed from the system, eliminating the gas volume that would be subject to temperature-induced pressure changes per Boyle's law. Without a sealed gas volume, temperature cannot cause pressure drift, solving the temperature dependency problem
Solution Approach 2:
The patent uses two identical sensing elements that are differentially connected. Both elements experience the same temperature effects, and by subtracting their outputs, common-mode temperature drift is rejected, further eliminating temperature dependency
4Reliability
If out-gassing of layers in the reference cavity is prevented, then recalibration is reduced, but the manufacturing process becomes more complex
Solution Approach 1:
The reference cavity is extracted from the design, eliminating the sealed volume where out-gassing could occur. Without a sealed cavity containing layers that can out-gas, recalibration issues are eliminated and manufacturing is simplified as hermetic sealing processes are no longer required
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 approach enables accurate and stable pressure sensing across a range of pressures, reducing signal drift and temperature effects, with improved sensitivity and reduced calibration needs, suitable for diverse applications including automotive and medical uses.
Implementation Method 1
The actuator generates a force with a controlled frequency that causes movement of the membrane relative to the cavity, and thereby changes the volume of the chamber and generates a gas pressure inside the chamber
Implementation Method 2
The sensor detects a frequency-based characteristic of the membrane responsive to the change in volume, which influences the force of gas upon the membrane
Implementation Method 3
The membrane has a plurality of openings that pass gas into and out of the chamber, and moves in response to an actuation force
Data Source
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AI summary
As may be consistent with one or more embodiments discussed herein, an integrated circuit apparatus includes a membrane suspended over a cavity, with the membrane and cavity defining a chamber. The membrane has a plurality of openings therein that pass gas into and out of the chamber. As the membrane is actuated, the volume of the chamber changes to generate a gas pressure inside the chamber that is different than a pressure outside the chamber. A sensor detects a frequency-based characteristic of the membrane responsive to the change in volume, and therein provides an indication of the gas pressure outside the chamber.