MEMS Diaphragm Stepped Passage for Acoustic Ingress Protection
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Solution Overview
Problem
MEMS acoustic transducers face a challenge in balancing low-frequency roll-off (LFRO) performance with ingress protection, as thicker diaphragms require larger passages for the same performance, which increases vulnerability to water and particulate ingress.
Innovation Solution
A MEMS die with a diaphragm featuring a tapered or stepped passage geometry, where the cross-sectional area is smaller on the externally facing surface than the internally facing surface, effectively maintaining LFRO performance while enhancing ingress protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a larger passage is used in the diaphragm, then the low-frequency roll-off performance is improved, but the ingress protection is worsened
Solution Approach 1:
The passage is designed with non-uniform cross-sectional area, where the exterior-facing side has a smaller cross-sectional area than the interior-facing side. This local variation in geometry allows different regions of the passage to serve different functions: the smaller exterior side provides better ingress protection while the larger interior side maintains LFRO performance.
Solution Approach 2:
The passage geometry transitions from a two-dimensional circular cross-section to a three-dimensional tapered or stepped structure. By introducing dimensional variation along the passage length, the design achieves both small exterior area for protection and large interior area for acoustic performance simultaneously.
2Strength
If a thicker diaphragm is used, then the structural strength is improved, but the passage size must be increased to maintain LFRO performance
Solution Approach 1:
The passage cross-sectional area varies locally along its length, being smaller at the exterior side and larger at the interior side. This allows the passage to accommodate thicker diaphragm requirements while maintaining both LFRO performance and ingress protection through localized geometric optimization.
Solution Approach 2:
The passage geometry parameters (cross-sectional area, taper angle, step dimensions) are optimized to match the diaphragm thickness. By adjusting these parameters, the design maintains LFRO performance in thicker diaphragms while the smaller exterior cross-section provides enhanced ingress protection.
Data Source
AI summary
A MEMS die includes a substrate having an opening formed therein, a diaphragm having a first surface attached around a periphery thereof to the substrate and over the opening, and a backplate separated from a second surface of the diaphragm. The diaphragm includes at least one passage disposed between the first and second surfaces, and the at least one passage has a smaller cross-sectional area at the first surface than at the second surface.