MEMS Anchor Design Mitigating Shear Stress via Segmented Anchors
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Solution Overview
Problem
The existing two-sided anchoring method in MEMS devices, as seen in the Nasiri fabrication technique, is prone to shear stress when external forces are applied to the top substrate, degrading the device's performance, while one-sided anchors lack the benefits of two-sided anchoring such as simultaneous mechanical and electrical anchoring.
Innovation Solution
A modified anchoring system with a first portion rigidly connected to both substrates and a second portion rigidly connected only to the top substrate, coupled by a flexible mechanical element providing electrical connection and acting as a mechanical anchor, similar to surface micromachined anchors, to mitigate shear stress and enhance bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a two-sided anchor is used to provide simultaneous mechanical and electrical anchoring, then the anchoring strength and electrical connection are improved, but shear stress increases when external forces are applied to the top substrate
Solution Approach 1:
The anchor is divided into two distinct portions: a first portion that provides mechanical anchoring by being rigidly connected to both substrates, and a second portion that provides electrical anchoring by being rigidly connected only to the top substrate. This segmentation allows each portion to specialize in one function, reducing the shear stress on the mechanical anchor while maintaining electrical connection.
Solution Approach 2:
The flexible mechanical element acts as an intermediary between the first and second portions of the anchor. It provides the electrical connection between the mechanical anchor (first portion) and the electrical anchor (second portion) while accommodating mechanical stresses, thereby protecting the rigid mechanical anchor from shear stress.
2Stress or pressure
If a one-sided anchor is used to reduce shear stress, then the shear stress on the anchor is reduced, but the benefits of simultaneous mechanical and electrical anchoring are lost
Solution Approach 1:
The anchor system is segmented into two functional portions: the first portion rigidly connected to both substrates provides mechanical anchoring, while the second portion rigidly connected only to the top substrate provides electrical anchoring. This segmentation enables each portion to optimize for its specific function, maintaining anchoring reliability while reducing shear stress.
Solution Approach 2:
The patent merges the functions of mechanical anchoring and electrical anchoring into a single integrated anchor assembly with two portions. The flexible mechanical element connects both portions, combining the benefits of rigid mechanical support and rigid electrical connection while using the flexible element to manage stress distribution.
3Reliability
If thick films are deposited to increase proof mass height for low noise performance, then the noise performance is improved, but the fabrication complexity and cost increase
Solution Approach 1:
The patent replaces the surface micromachining approach (which requires complex deposition of thick films) with a bulk micromachining approach. The proof mass is formed by selectively etching the substrate to create deep cavities, allowing thick proof masses to be created without the need for sophisticated thick film deposition equipment and processes.
Solution Approach 2:
Instead of building up thick proof masses by depositing multiple layers of material (additive approach), the patent uses a subtractive approach by etching deep cavities into the substrate and forming proof masses within those cavities. This inversion of the manufacturing approach simplifies the fabrication process and reduces equipment requirements.
4Ease of manufacture
If surface micromachining is used to build structures with deposited layers, then the manufacturing process is established, but the fabrication cost and equipment requirements increase significantly
Solution Approach 1:
The patent replaces surface micromachining (which requires complex deposition equipment) with bulk micromachining techniques that use selective etching. This substitution eliminates the need for sophisticated thick film deposition equipment while maintaining the ability to manufacture MEMS devices, making the process accessible to smaller companies without extensive infrastructure.
Data Source
AI summary
An anchoring assembly for anchoring MEMS device is disclosed. The anchoring assembly comprises: a top substrate; a bottom substrate substantially parallel to the top substrate; and a first portion of the anchor between the top substrate and the bottom substrate. The first portion of the anchor is rigidly connected to the top substrate; and the first portion of the anchor is rigidly connected to the bottom substrate. A second portion of the anchor is between the top substrate and the bottom substrate. The second portion of the anchor is rigidly connected to the top substrate; the second portion of the anchor being an anchoring point for the MEMS device. A substantially flexible mechanical element coupling the first portion of the anchor and the second portion of the anchor; the flexible element providing the electrical connection between the first portion of the anchor and the second portion of the anchor.