Sealing Layer for Low Frequency MEMS Microphone Diaphragm
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Solution Overview
Problem
MEMS microphones face limitations in low-frequency response due to air leakage through slot channels in the diaphragm suspension design, which reduces sensitivity and acoustic performance, primarily due to the limitations of fabrication processes in creating very small slots.
Innovation Solution
Incorporating a sealing layer that spans the spring gap between the diaphragm and the backplate, with an equalization aperture to allow pressure equalization while preventing air leakage, thereby increasing acoustic resistance and improving frequency response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If slot channels are provided in the diaphragm suspension design to allow pressure equalization, then the microphone can sense acoustic waves, but air leakage through these slots reduces acoustic resistance and limits low-frequency response
Solution Approach 1:
The patent removes the slot channels from the diaphragm suspension design entirely. Instead of having slots that allow air leakage, the invention uses a sealed suspension structure where the diaphragm is suspended by springs or beams that are completely enclosed, eliminating the air leakage path while maintaining pressure equalization through alternative means.
Solution Approach 2:
The patent introduces a sealed cavity or alternative pressure equalization path that acts as an intermediary between the front and back of the diaphragm. This intermediary structure allows pressure to equalize without creating direct air leakage channels that would reduce acoustic resistance.
2Loss of energy
If the slot width is reduced to increase acoustic resistance, then low-frequency response improves, but fabrication precision requirements increase due to photolithography and etching limits
Solution Approach 1:
The patent eliminates the slot structure entirely from the design, removing the need to fabricate precise narrow slots. The suspension structure is redesigned to achieve the desired acoustic resistance without relying on tight tolerances in slot dimensions, thereby avoiding the photolithography and etching precision limitations.
Solution Approach 2:
The patent changes the fundamental geometric parameters of the suspension structure by replacing slot-based pressure equalization with a sealed design. This parameter change allows the acoustic resistance to be controlled by the dimensions of the sealed cavity or alternative equalization path rather than by the narrow slot dimensions that are difficult to fabricate precisely.
3Loss of energy
If slot geometry is optimized to increase acoustic resistance, then low corner frequency decreases, but the complexity of spring channel slot geometry design increases
Solution Approach 1:
The patent removes the complex slot geometry from the design entirely. By eliminating the slots, the invention simplifies the overall structure while achieving the desired acoustic resistance through the sealed suspension design and alternative pressure equalization mechanism.
Solution Approach 2:
The patent segments the pressure equalization function from the suspension structure. Instead of having slots integrated into the spring channels, the invention separates these functions by using a sealed suspension with a distinct cavity or alternative path for pressure equalization, thereby simplifying the suspension geometry design.
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 sealing layer enhances the low-corner frequency and dynamic range of MEMS microphones by effectively sealing the spring gap, improving acoustic performance and sensitivity by impeding air flow through the diaphragm, thus allowing for better acoustic energy transfer.
Implementation Method 1
The impedance of these channels is represented by a resistance, which considers losses due to viscous resistance of air passing through them
Implementation Method 2
A MEMS microphone measures the instantaneous differential pressure between opposing sides of diaphragm
Implementation Method 3
the backplate and diaphragm form a variable capacitor of a microphone
Data Source
AI summary
A microphone system includes a diaphragm suspended by springs and including a sealing layer that seals passageways which, if left open, would degrade the microphone's frequency response by allowing air to pass from one side of the diaphragm to the other when the diaphragm is responding to an incident acoustic signal. In some embodiments, the sealing layer may include an equalization aperture to allow pressure to equalize on both sides of the diaphragm.