MEMS Microphone Insulation Layer Band Stop Filter Noise
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Solution Overview
Problem
MEMS microphones face challenges in reducing noise generated by acoustic holes in the back plate, which affects the Signal-to-Noise Ratio (SNR) characteristics.
Innovation Solution
The design incorporates a substrate with a vibration area, supporting area, and peripheral area, featuring a diaphragm and back plate with air gaps, insulation layers, and strategically placed acoustic holes and slits to form spaces that act as band stop filters, attenuating specific frequencies and improving SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If acoustic holes are formed in the back plate to allow acoustic wave passage, then the microphone can function, but noise is generated that degrades SNR characteristics
Solution Approach 1:
The acoustic holes are segmented into two distinct types: first acoustic holes in the back plate for acoustic wave passage, and second acoustic holes in the upper insulation layer for etchant flow. This segmentation allows each type of hole to serve its specific function independently, preventing noise generation while maintaining acoustic functionality.
Solution Approach 2:
The upper insulation layer acts as an intermediary structure that introduces second acoustic holes as a mediator pathway. This intermediary layer allows etchant to reach the substrate through a separate path (second acoustic holes) from the acoustic wave path (first acoustic holes), thereby eliminating noise generation while preserving acoustic functionality.
2Object-generated harmful factors
If the back plate is held spaced apart from the diaphragm to form an air gap, then noise is reduced, but additional insulation layers and chamber portions are required
Solution Approach 1:
The upper insulation layer serves multiple functions simultaneously: it holds the back plate spaced apart from the diaphragm to reduce noise, provides a pathway for etchant flow through second acoustic holes, and supports the structural integrity of the device. This multi-functionality reduces the need for additional separate components.
Solution Approach 2:
The chamber portions are merged with the supporting area structure, and the insulation layers are integrated to perform both mechanical support and acoustic isolation functions. This merging reduces the overall device complexity by combining multiple functions into unified structures rather than adding separate components.
3Object-generated harmful factors
If spaces are formed outside chamber portions communicating with slits, then band stop filter functionality is achieved for noise attenuation, but manufacturing steps increase
Solution Approach 1:
The spaces are formed during the manufacturing process by strategically removing the lower insulation layer and intermediate insulation layer in specific regions before final assembly. This preliminary formation of spaces integrated into the manufacturing flow eliminates the need for post-manufacturing steps to create the band stop filter structure.
Solution Approach 2:
The spaces are nested within the existing layer structure by removing specific insulation layers in defined regions. The spaces are formed by nesting the removal process within the multi-layer insulation structure, allowing the band stop filter functionality to be integrated without adding external components or complex assembly steps.
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 solution effectively reduces noise components in the acoustic signal, enhancing the signal-to-noise ratio by utilizing the spaces between chamber portions and air gaps to function as band stop filters, thereby improving the microphone's performance.
Implementation Method 1
the diaphragm being spaced apart from the substrate to be configured to sense an acoustic pressure to generate a corresponding displacement
Implementation Method 2
utilizing the spaces between chamber portions and air gaps to function as band stop filters, thereby improving the microphone's performance
Data Source
AI summary
A MEMS microphone includes a substrate, a diaphragm disposed over the substrate to cover the cavity, the diaphragm defining an air gap together with the back plate, and the diaphragm being spaced apart from the substrate, a back plate disposed over the diaphragm and in the vibration area, an upper insulation layer to cover the back plate, a plurality of chamber portions provided in the supporting area, a lower insulation layer provided under the upper insulation layer and on the substrate, and an intermediate insulation layer provided between the lower insulation layer and the upper insulation layer and disposed further from the vibration area than the chamber portions.