MEMS Microphone Aperture Design for Sensitivity and Production
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Solution Overview
Problem
The existing production process for MEMS microphones is time-intensive and prone to errors due to the need for precise rear-side etching processes to achieve high microphone sensitivity, which requires expensive and precise adjustments and low etching rates.
Innovation Solution
Incorporating an acoustically transparent aperture in an enclosing layer between the diaphragm and the substrate, allowing the rear-side volume to extend laterally beyond the aperture, thereby avoiding acoustic short-circuits and enabling larger rear-side volumes with easier production and precise positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a rear-side etching process is used to create the rear-side volume, then the microphone sensitivity can be improved, but the production process becomes time-intensive and expensive due to the need for precise matching and low etching rates
Solution Approach 1:
The aperture is created in the enclosing layer during the front-side layer construction process, before the rear-side etching takes place. This preliminary action defines the opening position and size in advance, eliminating the need for time-consuming precise matching during rear-side etching while maintaining high microphone sensitivity
Solution Approach 2:
The aperture creation is separated from the rear-side etching process. The aperture is formed independently in the enclosing layer during front-side processing, while the rear-side etching can proceed at higher rates without compromising precision requirements
2Measurement precision
If the rear-side etching mask is precisely adjusted to match the microphone structure, then the microphone sensitivity is maximized, but the production process becomes expensive and complex
Solution Approach 1:
The aperture position and size are predetermined during the front-side layer construction process. This preliminary definition of the opening eliminates the need for complex and expensive precise adjustment of rear-side etching masks, while ensuring optimal microphone sensitivity
Solution Approach 2:
The enclosing layer with its pre-defined aperture acts as an intermediary structure that decouples the front-side microphone structure from the rear-side etching process. This intermediary allows independent optimization of both processes without requiring precise matching between them
3Measurement precision
If the rear-side volume is made large to reduce signal attenuation, then the microphone sensitivity is improved, but the rear-side etching process becomes more difficult and time-consuming
Solution Approach 1:
The aperture dimensions are predetermined during front-side processing to provide sufficient opening area for acoustic coupling. This allows the rear-side etching to create a large volume without being constrained by the need to precisely define the opening during etching, thereby reducing etching time while maintaining sensitivity
4Strength
If bypass openings or web-type spring elements are used in the edge region of the diaphragm, then the diaphragm suspension is improved, but acoustic short-circuits occur if the connecting opening extends over the diaphragm surface
Solution Approach 1:
The aperture in the enclosing layer is positioned and sized to provide local acoustic coupling only where needed (over the closed center region of the diaphragm), while allowing bypass openings in the edge region to function without causing short-circuits. This localized approach maintains both suspension integrity and acoustic performance
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 approach simplifies the production method, reduces the risk of errors, and enhances microphone sensitivity by allowing for larger rear-side volumes and precise aperture placement, while maintaining high measurement sensitivity and low electromagnetic interference.
Implementation Method 1
a diaphragm (11) which is deflectable by acoustic pressure
Implementation Method 2
detect acoustic pressure in the form of a change in capacitance between the acoustically active diaphragm and the largely rigid counter-element
Implementation Method 3
at least one enclosing layer (3) in which there is fashioned an acoustically transparent aperture (4)
Data Source
AI summary
Measures are provided for improving the acoustic properties of a component (10) having a micromechanical microphone structure realized in a layer construction (20) over a substrate (1), and for simplifying the production method. The microphone structure of such a component (10) includes a diaphragm (11) deflectable by acoustic pressure, spanning a cavity (13) that acts as a rear-side volume in the rear side of the component, and includes a stationary, acoustically permeable counter-element (12) situated over the diaphragm (11). According to the invention, the layer construction (20) has, between the diaphragm (11) and the substrate (1), an enclosing layer (3) in which there is fashioned an acoustically transparent aperture (4). The diaphragm (11) is connected to the rear-side volume (13) via this aperture in the enclosing layer (3). Under the enclosing layer (3), the rear-side volume (13) extends laterally beyond this aperture (4).