Collapsed Mode Capacitive Sensor Segmented Membrane
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Solution Overview
Problem
Miniature silicon capacitive microphones face challenges in achieving high sensitivity and low noise with small volumes, as conventional manufacturing processes like through-wafer etching are time-consuming and costly, and integrated circuit materials struggle with membrane compliance and stress issues.
Innovation Solution
The capacitive sensor operates in a 'collapsed mode' with a segmented membrane, eliminating the need for through-wafer etching and using micro-machined semiconductor substrates with segmented membranes supported by insulating structures, enhancing sensitivity and reducing stress, and allowing for simpler fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If through-wafer etching is used to create separation of membrane and back plate layer, then manufacturing precision is improved, but manufacturing time and cost increase significantly
Solution Approach 1:
The back plate is divided into multiple separate legs that are selectively removed in specific regions. This segmentation allows the membrane to be separated from the back plate in defined areas without requiring through-wafer etching, thereby reducing manufacturing time while maintaining precision where separation is needed.
Solution Approach 2:
Specific portions of the back plate are selectively removed or etched away in regions where membrane separation is required. This extraction approach avoids the need for complete through-wafer etching, significantly reducing manufacturing time while achieving the necessary separation for capacitor formation.
2Volume of moving object
If membrane size is reduced to achieve small volume, then device size is improved, but sensitivity and noise performance deteriorate
Solution Approach 1:
The membrane is divided into multiple segmented regions with different properties. This segmentation allows optimization of different areas: central regions can be designed for high sensitivity while peripheral regions maintain structural integrity, enabling small overall device volume without sacrificing measurement precision.
Solution Approach 2:
Different regions of the membrane are designed with locally optimized properties. The membrane thickness, material composition, and stress characteristics are varied across different zones to achieve high sensitivity in measurement regions while maintaining structural stability, thereby improving signal-to-noise ratio in a compact device.
3Measurement precision
If membrane is made highly compliant for good acoustic response, then sensitivity to sound is improved, but stress control becomes difficult leading to buckling
Solution Approach 1:
The membrane is segmented into multiple regions with different compliance characteristics. This allows highly compliant regions for acoustic sensitivity while other regions provide structural support and stress management, preventing buckling even when overall compliance is high.
Solution Approach 2:
The membrane exhibits spatially varying properties with different regions having different thicknesses, materials, or stress states. This local quality variation enables highly compliant areas for sound detection while adjacent regions maintain structural stability and prevent buckling under operational conditions.
4Measurement precision
If segmented membrane structure is implemented, then stress control and sensitivity are improved, but device complexity increases
Solution Approach 1:
The segmented membrane structure is integrated with the back plate legs and support structures as a unified device architecture. This merging of components reduces overall device complexity compared to implementing segmentation as separate added elements, while still achieving stress control and sensitivity improvements through the integrated segmented design.
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 achieves high sensitivity and low noise with improved signal-to-noise ratio, increased robustness, and faster fabrication, enabling effective pressure and sound measurement without the need for through-wafer cavities, and allows for increased resonance frequencies.
Implementation Method 1
capacitive sensor with improved functionality... sensitivity for pressure changes is large, providing good pressure measurement. The collapsed mode sensor of the invention also provides good sensitivity to sound.
Data Source
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AI summary
A capacitive sensor is configured for collapsed mode, e.g. for measuring sound or pressure, wherein the moveable element is partitioned into smaller sections. The capacitive sensor provides increased signal to noise ratio.