MEMS Pressure Sensor Deformable Cavity Acoustic Resistance
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Solution Overview
Problem
MEMS microphones face challenges such as significant sensitivity loss due to numerous holes for acoustic resistance reduction, limited usable surface area for capacitive detection, and non-linear response to acoustic pressure, along with manufacturing variability and sensitivity to environmental factors.
Innovation Solution
A MEMS pressure sensor design featuring a deformable cavity with a movable wall in the plane of the substrate, allowing pressure variations to be detected independently of the electrical measurement, using capacitive or strain gauge detection methods, and incorporating a secondary cavity for filtering rapid fluctuations and optimizing sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the number of holes in the fixed electrode is increased to reduce acoustic resistance, then the acoustic resistance is reduced, but the useful surface area for capacitive detection is reduced
Solution Approach 1:
The fixed electrode is segmented into multiple discrete holes rather than a continuous structure, allowing acoustic waves to pass through while maintaining sufficient solid surface area for capacitive detection. The holes are strategically positioned and sized to balance acoustic transmission with detection surface area.
Solution Approach 2:
Different regions of the fixed electrode have different properties: the holes provide acoustic transmission pathways while the solid regions between holes provide capacitive detection surface. This local differentiation allows simultaneous optimization of both acoustic resistance and detection area.
2Measurement precision
If the air gap between the membrane and fixed electrode is reduced to increase sensitivity, then the capacitive detection sensitivity is improved, but the measurement noise increases and pull-in voltage limits are approached
Solution Approach 1:
The system operates in a dynamic regime where the membrane oscillates in response to acoustic pressure. By optimizing the air gap for resonant operation rather than static proximity, the system achieves high sensitivity while maintaining stable operation away from pull-in conditions.
Solution Approach 2:
The membrane undergoes periodic oscillation driven by acoustic pressure variations. This periodic motion converts small pressure changes into larger displacement amplitudes at resonant frequencies, enhancing sensitivity without requiring the membrane to be in constant close proximity to the electrode.
3Stability of the object's composition
If the membrane is embedded on its periphery to provide mechanical support, then the structural stability is improved, but the usable deformation surface area is reduced
Solution Approach 1:
The membrane is supported at its periphery rather than being fully clamped, creating an asymmetric support structure that allows the central region to deform freely. This peripheral embedding provides mechanical stability while maximizing the active deformation area in the center.
Solution Approach 2:
The membrane structure is divided into a supported peripheral region and a free central region. The peripheral region provides mechanical support and stability, while the central region undergoes maximum deformation for sensing, effectively segmenting the membrane into functional zones.
4Device complexity
If the membrane serves both as mechanical spring and mobile electrode to simplify structure, then the device complexity is reduced, but the sensitivity and acoustic performance are compromised
Solution Approach 1:
The device is segmented into separate functional components: the membrane serves as the mechanical spring and acoustic receiver, while the fixed electrode serves as the detection electrode. This segmentation allows each component to be optimized for its specific function rather than compromising performance for structural simplicity.
Solution Approach 2:
The detection electrode function is extracted from the membrane and placed in the fixed electrode structure. This separation allows the membrane to be optimized purely for mechanical response to acoustic pressure, while the fixed electrode is optimized for capacitive detection, improving overall sensitivity.
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 3A~4
AI summary
The invention relates to a MEMS and/or NEMS type pressure sensor comprising: - at least a first deformable cavity (20) for receiving pressure variations of an ambient atmosphere, this first deformable cavity being made in a first substrate and comprising at least one movable or deformable wall (25), disposed at least in part in the plane parallel to the first substrate, called the sensor plane, and means (21) for transmitting pressure variations of an ambient atmosphere to this cavity, - detection means (24, 24') for detecting a displacement or deformation, in the sensor plane, of said movable or deformable wall, under the effect of a pressure variation of the ambient atmosphere.