MEMS Microphone Anchor Etching for Parasitic Capacitance
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Solution Overview
Problem
MEMS microphones face challenges in achieving improved signal quality and reduced lower limiting frequency (LLF) due to constraints in miniaturization, which are exacerbated by parasitic capacitance and limited control over production processes, leading to mechanical instability and short ventilation paths.
Innovation Solution
The use of different etching rates within the same layer for sacrificial materials allows precise control of lateral dimensions, reducing the bearing area of anchors and enabling longer ventilation paths, thus minimizing parasitic capacitance and achieving smaller microphone dimensions while maintaining mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the bearing area of the substrate-side anchor is reduced to minimize parasitic capacitance, then signal quality is improved, but mechanical stability deteriorates
Solution Approach 1:
The patent applies local quality by creating regions with different etching rates within the same sacrificial material layer. Specifically, the anchor region is treated to have a reduced etching rate compared to surrounding areas, allowing the anchor bearing area to be precisely controlled at the minimum required for mechanical stability while minimizing parasitic capacitance in other regions.
Solution Approach 2:
The patent changes the etching rate parameter locally within the sacrificial material layer. By modifying the etching rate in the anchor region (making it slower) versus other regions (faster), the invention achieves precise control over the anchor bearing area, allowing it to be exactly sized at the minimum required for mechanical stability while minimizing overall parasitic capacitance.
2Volume of moving object
If the microphone is miniaturized to reduce device size, then productivity is improved, but signal quality deteriorates due to reduced back volume
Solution Approach 1:
The patent applies local quality by differentiating etching rates between the anchor region and other regions of the sacrificial material. This allows the anchor bearing area to be precisely minimized without compromising mechanical stability, thereby reducing overall microphone size while maintaining signal quality through optimized parasitic capacitance management.
Solution Approach 2:
The patent uses partial action by selectively applying reduced etching rate only to the anchor region where mechanical stability is critical, while allowing faster etching in other regions to minimize parasitic capacitance and reduce overall device size. This partial differentiation enables simultaneous achievement of miniaturization and signal quality.
3Measurement precision
If the ventilation path is lengthened to reduce lower limiting frequency, then LLF is improved, but device complexity increases due to production constraints
Solution Approach 1:
The patent changes the etching rate parameter in the sacrificial material layer to enable precise control over the ventilation path geometry. By adjusting etching rates in different regions, the invention achieves the required ventilation path length for reduced LLF without adding complex production steps, as the etching process itself creates the desired geometry.
4Object-affected harmful factors
If the bearing area of the substrate-side anchor is minimized, then parasitic capacitance is reduced, but control over production processes becomes more difficult
Solution Approach 1:
The patent applies local quality by creating distinct regions with different etching rates within the sacrificial material layer. The anchor region has a reduced etching rate while other regions have normal etching rates, allowing the bearing area to be precisely controlled at minimum dimensions required for stability while minimizing parasitic capacitance elsewhere.
Solution Approach 2:
The patent changes the etching rate parameter locally in the anchor region to a reduced value, enabling precise control over the bearing area dimension. This parameter modification allows the bearing area to be exactly sized at the minimum required for mechanical stability, achieving minimal parasitic capacitance while maintaining production process control.
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 results in improved signal quality and reduced LLF, allowing for the production of smaller MEMS microphones with enhanced mechanical stability and longer ventilation paths, which compensate for smaller back volumes.
Implementation Method 1
setting lateral dimensions very precisely by means of different etching rates within the same layer. Particularly the etching rates of regions within the same layer which contains a sacrificial material are used for this purpose.
Data Source
AI summary
A MEMS microphone with improved sensitivity and a method for producing such a MEMS microphone are disclosed. In an embodiment the MEMS microphone includes a carrier substrate, a capacitor having two electrodes, a substrate-side anchor and an electrode anchor, wherein the substrate-side anchor connects the substrate to the capacitor, wherein the electrode anchor connects the two electrodes of the capacitor, wherein one of the electrodes is a backplate and the other electrode is the anchored membrane, and wherein the substrate-side anchor has a bearing area on the substrate which exceeds a minimum area necessary for a mechanical stability of the MEMS microphone by not more than the minimum area.