Graded Concave MEMS Support Structure for Stress Distribution
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Solution Overview
Problem
Current methods for fixing membranes in MEMS transducers impose stress on the membranes at fixing points, leading to premature failure due to abrupt transitions and high-stress zones, which hinders miniaturization and performance.
Innovation Solution
A graded, concave-tapered holding structure is used to distribute stress across a curved surface instead of concentrating it at sharp edges, achieved through varying etch rates and material composition, such as silicon oxinitride with graded nitrogen content, to form a composite structure that mitigates stress during membrane deflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a membrane is fixed to a carrier using conventional support structures, then the membrane can be suspended and functional, but stress concentrations occur at fixing points leading to premature failure
Solution Approach 1:
The support structure employs a rounded, concave shape instead of sharp edges or flat surfaces. This curvature distributes the mechanical stress across a broader area of the membrane, eliminating stress concentration points that would otherwise lead to premature failure. The rounded geometry allows stress to flow smoothly through the structure rather than concentrating at corners or abrupt transitions.
Solution Approach 2:
The support structure features a tapered geometry where the cross-sectional area varies along its length, with a wider base transitioning to a narrower top. This local variation in geometry optimizes the structure for its specific function: the wider base provides structural support and stress distribution, while the narrower top maintains proper spacing for membrane operation. Each portion of the structure has optimized properties for its local requirements.
2Length of moving object
If membrane thickness is reduced for miniaturization, then device size decreases, but membrane strength and resistance to stress diminish
Solution Approach 1:
The rounded, concave support structure reduces stress concentrations on the membrane by distributing loads across curved surfaces rather than sharp edges. This geometric feature protects thin membranes from stress-induced failure, enabling miniaturization without sacrificing membrane strength or reliability.
Solution Approach 2:
The tapered support structure provides optimized local geometry where the wider base offers maximum structural support and stress distribution, while the narrower top maintains appropriate spacing for transducer operation. This localized optimization allows thin membranes to be used throughout the device while maintaining overall structural integrity.
3Ease of manufacture
If conventional support structures with sharp edges are used, then manufacturing is simpler, but stress concentrations cause premature membrane failure
Solution Approach 1:
The rounded, concave support structure can be fabricated using standard semiconductor processing techniques such as anisotropic etching of silicon or deposition of curved-profile materials. While the geometry is more complex than simple sharp-edged structures, modern manufacturing capabilities can produce these curved profiles with sufficient precision to achieve both the desired stress distribution and acceptable manufacturing complexity.
Data Source
AI summary
A structure for fixing a membrane to a carrier including a carrier; a suspended structure; and a holding structure with a rounded concave shape which is configured to fix the suspended structure to the carrier and where a tapered side of the holding structure physically connects to the suspended structure is disclosed. A method of forming the holding structure on a carrier to support a suspended structure is further disclosed. The method may include: forming a holding structure on a carrier; forming a suspended structure on the holding structure; shaping the holding structure such that it has a concave shape; and arranging the holding structure such that a tapered side of the holding structure physically connects to the suspended structure.