CNT Templated Fabrication of High Aspect Ratio Free Standing Posts
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Solution Overview
Problem
The challenge lies in fabricating high aspect ratio tall free standing posts using carbon-nanotube templated microfabrication, as direct growth techniques often result in posts that bend or break due to their tall and thin nature, losing vertical structure integrity.
Innovation Solution
The method involves growing carbon nanotubes with supporting structures using CNT-M techniques, followed by plasma etching to remove the sacrificial structures, allowing for the creation of free-standing posts with aspect ratios greater than 25:1, achieved through a combination of non-directional and directional plasma etching and carbon infiltration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If direct growth techniques are used to fabricate tall carbon nanotube posts, then the height of the posts can be increased, but the posts bend or break due to their tall and thin nature, losing vertical structure integrity
Solution Approach 1:
The patent applies preliminary action by growing supporting structures (such as sacrificial mandrels or temporary support frameworks) before growing the carbon nanotube posts. These pre-formed supporting structures provide mechanical stability during the CNT growth process, preventing bending and breaking of tall, thin posts. After growth, the supporting structures are removed, leaving intact free-standing high aspect ratio posts.
Solution Approach 2:
The patent uses intermediary supporting structures as mediators between the substrate and the tall carbon nanotube posts during fabrication. These intermediaries (such as sacrificial layers or temporary supports) provide the necessary mechanical support during and after CNT growth, enabling the formation of stable high aspect ratio structures that would otherwise collapse under their own weight.
2Stability of the object's composition
If carbon nanotubes are grown to form free standing posts with high aspect ratio, then the posts maintain vertical orientation and structural integrity, but the fabrication process becomes complex requiring multiple steps including plasma etching and carbon infiltration
Solution Approach 1:
The patent segments the fabrication process into distinct stages: forming supporting structures, growing carbon nanotubes on these supports, removing the supporting structures through plasma etching, and performing carbon infiltration. This segmentation allows each step to be optimized independently, managing the overall process complexity while achieving high aspect ratio free-standing posts with excellent vertical integrity.
Solution Approach 2:
The patent employs parameter changes by varying plasma etching conditions (directional vs. non-directional etching, power, pressure, gas composition) and carbon infiltration parameters (temperature, time, carbon source) to selectively remove supporting structures while preserving the carbon nanotube posts. These parameter adjustments enable precise control over the fabrication process complexity.
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 enables the production of millimeter-tall carbon nanotube posts with diameters ranging from 10-40 μm, maintaining vertical orientation and structural integrity, which is crucial for various applications including biochemical sensing and integration with microelectronics.
Implementation Method 1
growing carbon nanotubes on the patterned catalyst layer to form the first carbon nanotube post, the second carbon nanotube post and the supporting structure
Implementation Method 2
followed by plasma etching to remove the sacrificial structures
Data Source
AI summary
In a general aspect, an apparatus can include a substrate and a post disposed on the substrate. The post can include a plurality of nanotubes and extend substantially vertically from the substrate. The post can have an aspect ratio of a height of the post to a diameter of the post of greater than or equal to 25:1.