CNT Memory Cell Selective Fabrication via Vertical Growth
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Solution Overview
Problem
The fabrication of memory devices using reversible resistivity-switching materials is technically challenging due to the difficulty in etching carbon nano-tube (CNT) materials with rough surface topography, leading to increased costs and complexity in integrated circuits.
Innovation Solution
A method is developed to selectively fabricate CNT materials using a seeding layer, eliminating the need for etching the CNT material by forming a reversible resistance-switching element with vertically aligned CNTs, which are grown or deposited over a conductor and a diode, allowing for the creation of non-volatile memory cells with improved fabrication simplicity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon nano-tube (CNT) material is used as reversible resistivity-switching material, then non-volatile memory functionality is achieved, but fabrication complexity and cost increase due to difficulty in etching CNT material with rough surface topography
Solution Approach 1:
The patent extracts the problematic etching step from the fabrication process by using vertically aligned CNTs grown on catalyst layers that are selectively removed. The CNTs are grown in a forest-like structure and then released from the substrate, eliminating the need to etch rough CNT material while maintaining the memory functionality.
Solution Approach 2:
Instead of attempting to etch the CNT material directly, the invention inverts the approach by growing CNTs vertically and then removing the substrate they are grown on. This allows the CNTs to be transferred to the final device structure without requiring etching of the CNT material itself, thus reducing fabrication complexity.
2Quantity of substance
If conventional CNT fabrication methods are used, then CNT material is formed, but surface topography becomes rough making subsequent processing difficult
Solution Approach 1:
The patent applies local quality by creating vertically aligned CNTs with uniform orientation and spacing through controlled growth on catalyst layers. The CNTs are grown in specific locations with controlled density, providing consistent surface properties that facilitate subsequent processing while maintaining the required CNT material quantity.
Solution Approach 2:
The invention changes the growth parameters of CNTs to achieve vertical alignment rather than random orientation. By controlling the growth conditions and catalyst layer properties, the CNTs develop uniform height, diameter, and spacing, transforming the surface topography from rough to controlled and predictable.
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 simplifies the fabrication of memory cells by avoiding the need to etch the CNT material, reducing fabrication costs and complexity, while ensuring vertical current flow and minimizing lateral conduction between memory cells, thus enhancing the reliability and efficiency of the memory devices.
Implementation Method 1
selectively fabricating a carbon nano-tube (CNT) material above the first conductor
Implementation Method 2
reversible resistance-switching element formed from carbon nano-tube (CNT) material
Data Source
AI summary
In some aspects, a method of fabricating a memory cell is provided that includes (1) fabricating a first conductor above a substrate; (2) selectively fabricating a carbon nano-tube (CNT) material above the first conductor; (3) fabricating a diode above the CNT material; and (4) fabricating a second conductor above the diode. Numerous other aspects are provided.