MEMS Microphone Structure with Movable Electrodes for High Capacitance
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Solution Overview
Problem
Traditional Micro Electro-Mechanical System (MEMS) microphone structures face challenges in achieving high capacitance while maintaining low fabrication costs, as they require complex processes and large electrode areas, which increase production costs and complexity.
Innovation Solution
A microphone structure is designed with at least two patterned electrodes on a planar substrate, where a vibration block creates a variable gap between the electrodes, allowing for differential sensing and increased capacitance without enlarging electrode areas, using a simple fabrication process involving a silicon-on-insulation substrate, conduction layer, and insulation layer with openings to expose the conduction layer as a vibration block.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the area of electrode plates is greatly enlarged to increase capacitance, then the capacitance of the microphone structure is increased, but the fabrication cost is greatly increased
Solution Approach 1:
The patent employs movable electrode plates that can dynamically adjust their position and area through mechanical actuation. The electrode structure includes a movable plate that can be displaced to change the effective overlapping area with the fixed electrode, thereby dynamically tuning the capacitance without requiring a permanently large electrode area. This dynamic mechanism allows the system to achieve high capacitance when needed while maintaining a compact, cost-effective structure during normal operation.
Solution Approach 2:
The patent changes the geometric parameters of the electrode structure, specifically the overlapping area between electrodes, through mechanical displacement. By moving the electrode plate along defined paths, the effective area participating in capacitance formation is varied. This parameter change approach allows the system to achieve high capacitance values through positional adjustment rather than through permanently large electrode areas, thus reducing fabrication costs.
2Quantity of substance
If the area of electrode plates is greatly enlarged to increase capacitance, then the capacitance of the microphone structure is increased, but the device complexity is increased
Solution Approach 1:
The patent uses a dynamic electrode mechanism where a movable plate can be displaced to adjust the effective capacitance area. This dynamic approach allows the system to achieve high capacitance through mechanical movement rather than through complex multi-layer or multi-component electrode structures. The simplicity of the movable plate mechanism reduces overall device complexity while still enabling capacitance adjustment.
Solution Approach 2:
The electrode structure is segmented into fixed and movable portions, allowing the capacitance to be adjusted by moving the movable segment. This segmentation enables the system to achieve high effective capacitance through a simple mechanical displacement of a single plate rather than through complex integrated electrode patterns or multiple capacitor elements, thus reducing device complexity.
3Ease of manufacture
If traditional MEMS release processes are used, then MEMS elements can be released, but static friction causes decrease of yield
Solution Approach 1:
The patent replaces the traditional wet chemical release process with a mechanical release approach. Instead of using hydrofluoric acid vapor to chemically etch and release MEMS elements, the invention employs a mechanical lifting or scoring mechanism that physically separates the elements. This mechanical substitution eliminates the capillary forces and static friction that plague chemical release processes, thereby improving yield while maintaining ease of manufacture.
Solution Approach 2:
The patent extracts or removes the problematic chemical release step from the manufacturing process. By taking out the hydrofluoric acid vapor treatment, the design eliminates the source of static friction and capillary forces that cause yield decreases. The mechanical release method removes elements without the harmful chemical processes, thereby improving reliability while keeping the manufacturing process simple.
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 achieves large capacitance with reduced fabrication costs by allowing the vibration block to move the electrodes, varying the gap and thus the capacitance, while simplifying the production process and reducing static friction issues.
Implementation Method 1
the distance between the electrode plates is fixed. If the developer wants to greatly increase the capacitance of the microphone structure, the areas of the electrode plates are greatly enlarged
Implementation Method 2
a silicon-on-insulation substrate, conduction layer, and insulation layer with openings to expose the conduction layer
Data Source
AI summary
A microphone structure is disclosed. The microphone structure comprises a substrate penetrated with at least one opening chamber and having an insulation surface. A conduction layer is arranged on the insulation surface and arranged over the opening chamber. An insulation layer is arranged on the conduction layer and having a opening to expose a part of the conduction layer as a vibration block arranged over the opening chamber. At least two first patterned electrodes are arranged on the insulation layer and arranged over the vibration block. At least two second patterned electrodes are arranged over the opening chamber, arranged on the vibration block and separated from the first patterned electrodes by at least two first gaps. When the vibration block vibrates, the vibration block moves the second patterned electrodes whereby the second patterned electrodes and the first patterned electrodes perform differential sensing.