MEMS Microphone Blocking Layer for Noise Reduction
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Solution Overview
Problem
MEMS microphones suffer from mechanical noise due to air viscosity and low frequency roll-off issues caused by vent holes or slits, which affect signal-to-noise ratio and frequency response.
Innovation Solution
A MEMS structure is designed with a substrate, dielectric layer, membrane, backplate, and blocking layer, where the blocking layer is spatially isolated from the membrane but overlaps with vent holes, allowing for balanced sound pressure and reduced mechanical noise without obstructing the vent hole's function, and a method for fabricating this structure involves forming a dielectric layer, membrane with vent holes, blocking layer, and backplate, with careful etching to create chambers that communicate through the substrate and vent holes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If vent holes or slits are formed in the membrane to balance sound pressure, then mechanical noise is reduced and signal-to-noise ratio is improved, but low frequency roll-off occurs and frequency response is affected
Solution Approach 1:
A blocking layer is introduced as an intermediary component between the vent holes and the external environment. This blocking layer selectively blocks low frequency sound waves from passing through the vent holes while allowing higher frequency sound waves to pass through, thus reducing mechanical noise without causing low frequency roll-off. The blocking layer acts as a frequency-selective mediator that resolves the contradiction between noise reduction and frequency response maintenance.
2Volume of moving object
If the gap between membrane and backplate is reduced for compact size, then device miniaturization is achieved, but air viscosity generates stronger resistant force and mechanical noise increases
Solution Approach 1:
The blocking layer serves as a mediator that modifies the airflow characteristics in the reduced gap between membrane and backplate. By selectively blocking certain frequency ranges while allowing others to pass through, the blocking layer reduces the overall viscous resistance and mechanical noise generated by air viscosity in the compact gap, thus enabling miniaturization without excessive noise.
3Reliability
If blocking layer is added to reduce low frequency roll-off, then frequency response is improved, but device complexity increases
Solution Approach 1:
The blocking layer is implemented as a thin film or shell structure that can be easily integrated into the existing MEMS microphone architecture. This thin film approach adds minimal complexity while effectively providing frequency-selective blocking to reduce low frequency roll-off. The thin film nature of the blocking layer allows it to be deposited using standard semiconductor fabrication processes, minimizing the increase in device complexity.
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 improves the signal-to-noise ratio and frequency response of MEMS devices by reducing mechanical noise and alleviating low frequency roll-off, while maintaining the sound pressure balancing function of the vent holes.
Implementation Method 1
the blocking layer is spatially isolated from the membrane and at least partially overlaps with the at least one vent hole
Implementation Method 2
at least one slit or a vent hole is formed in the membrane to balance the sound pressure in the MEMS microphone
Implementation Method 3
When the membrane is subjected to sound pressure, vibrations which can cause a micro-distance change or result in dynamic micro-displacement between the membrane and the back plate may occur
Data Source
AI summary
A MEMS structure includes a substrate, a dielectric layer, a membrane, a backplate, and a blocking layer. The substrate has a through-hole. The dielectric layer is disposed on the substrate and has a cavity in communication with the through-hole. The membrane has at least one vent hole, is embedded in the dielectric layer and together with the dielectric layer defines a first chamber that communicates with the through-hole. The backplate is disposed on the dielectric layer. One end of the blocking layer is embedded in the dielectric layer, and the other end of the blocking layer extends into the cavity; the blocking layer is spatially isolated from the membrane and at least partially overlaps with the at least one vent hole.