MEMS Microphone Package Acoustic Low-Pass Filter Design
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Solution Overview
Problem
Miniaturized MEMS microphones suffer from low mechanical stability and nonlinear frequency response, leading to resonant magnifications and susceptibility to contamination, which impairs transmission quality and increases the risk of membrane damage.
Innovation Solution
A microphone package design featuring a substrate-mounted MEMS microphone chip, a cover for tight sealing, and a cavity system with a geometry that forms an acoustic low-pass filter with a −3 dB attenuation point below the natural resonances of the membrane, reducing high-frequency excitation and enhancing mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the MEMS microphone is miniaturized, then the size is reduced, but the mechanical stability decreases and the membrane becomes more susceptible to fracture
Solution Approach 1:
The patent introduces a damping layer between the membrane and the substrate that absorbs mechanical energy and dampens vibrations before they can cause damage to the membrane. This cushioning effect is built into the microphone structure to protect the fragile membrane from fracture during operation and drop tests, directly addressing the mechanical stability issue in miniaturized devices.
2Volume of moving object
If the distance between sound entry opening and membrane is shortened for miniaturization, then the size is reduced, but the membrane becomes more susceptible to contaminants and resonant magnifications increase
Solution Approach 1:
The patent introduces a damping layer as an intermediary component between the membrane and the sound channel. This layer serves multiple functions: it dampens resonant vibrations to reduce magnification effects, and it acts as a barrier that prevents contaminants from the sound channel from reaching and depositing on the membrane surface, thus addressing both resonance and contamination issues.
Solution Approach 2:
The damping layer is filled with damping material that creates viscous damping effects, using pneumatic principles to dissipate acoustic energy and reduce resonant magnifications. The material's viscosity and porosity are optimized to provide effective damping while maintaining acoustic transmission properties.
3Measurement precision
If the microphone membrane is made thinner for miniaturization, then the sensitivity is improved, but the mechanical strength decreases and fracture risk increases
Solution Approach 1:
The damping layer is positioned immediately behind the membrane to provide cushioning support. This allows the membrane to be made thinner for improved sensitivity while the damping layer prevents excessive vibrations and mechanical stress that would otherwise cause fracture, thus enabling thin membranes to maintain both sensitivity and mechanical strength.
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 effectively attenuates natural resonances, improving linearity of frequency response, increasing mechanical stability, and protecting the microphone from damage in drop tests while maintaining acoustic performance and sensitivity below the cut-off frequency.
Implementation Method 1
the at least one sound entry opening, the channel and the front volume form a cavity system and have a geometry defined such that an air friction arises and the cavity system forms an acoustic low-pass filter
Implementation Method 2
an electrically conductive membrane serves as an acoustoelectric sound transducer, said membrane forming a varying capacitance with respect to a counterelectrode under the action of sound
Data Source
AI summary
A microphone package wherein an MEMS microphone chip (MIC) is mounted on a substrate (SUB) and is sealed with a cover (ABD) with respect to the substrate. The membrane (MMB) of the microphone chip is connected to a sound entry opening (SEO) in the substrate via an acoustic channel. As a result of defined dimensioning of, in particular, the cross section and length of sound entry opening and channel, an acoustic low-pass filter is formed, the −3 dB attenuation point of which is significantly below the natural resonance of microphone membrane and package.