MEMS Microphone Membrane Small Holes Pressure Equalization
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Solution Overview
Problem
MEMS microphones face damage from extreme air pressure due to high pressure drops between the membrane and backplate, which existing solutions like adjustable ventilation openings or central vent holes compromise low-frequency roll-off accuracy.
Innovation Solution
A MEMS microphone component with a membrane featuring numerous small holes (diameter < 5 μm) for rapid pressure equalization, allowing for robustness against high pressures while maintaining low-frequency performance, and additional larger holes for etchant access during fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adjustable ventilation openings or central vent holes are used in the membrane, then pressure equalization between front volume and back volume is improved, but low-frequency roll-off accuracy deteriorates
Solution Approach 1:
The ventilation function is segmented into multiple small holes distributed across the membrane surface, rather than using a single central vent hole or adjustable opening. This segmentation allows pressure equalization while maintaining acoustic performance by distributing the venting effect across many small apertures.
Solution Approach 2:
The parameters of the ventilation holes are optimized: diameters between 0.5-5 μm (preferably 1-3 μm) and specific hole densities (e.g., 100-1000 holes per cm²). These parameter changes enable fast pressure equalization while minimizing impact on low-frequency roll-off characteristics.
2Reliability
If larger ventilation holes are used for fast pressure equalization, then robustness against high pressure is improved, but particle filtration capability deteriorates
Solution Approach 1:
The hole diameter is optimized to a specific range (0.5-5 μm, preferably 1-3 μm) that balances two competing requirements: small enough to filter particles larger than the hole diameter, yet sufficient to enable fast pressure equalization. This parameter optimization resolves the contradiction between pressure equalization speed and particle filtration.
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 design ensures fast pressure equalization and robustness against high pressures without compromising low-frequency roll-off accuracy, and prevents particle entry during production, ensuring reliable operation under extreme conditions.
Implementation Method 1
reducing the pressure drop over the membrane by equalizing the pressure between front volume and back volume of the microphone fast enough to keep the pressure drop low
Implementation Method 2
the flow resistance of a small hole exhibits a smaller increase with rising pressure drop than the flow resistance of a hole with a larger diameter. This can be explained by the less turbulent behavior of air flow through a small hole
Implementation Method 3
a first capacitor plate is formed by the membrane and a second capacitor plate is formed by the backplate. A bias voltage may be applied to the membrane or backplate. A deflection of the membrane due to acoustic pressure changes the capacitance between the membrane and backplate, resulting in an electric output signal
Data Source
AI summary
A microphone component and a method for fabricating a microphone component are disclosed. In an embodiment, a method includes fabricating a microphone component having a backplate and a membrane in a MEMS technology, forming a plurality of holes in the membrane, the holes having diameters smaller than 5 μm, choosing a value for a low frequency roll-off and a diameter of the holes in the membrane and choosing a number of holes such that the chosen value for low frequency roll-off is achieved.