Carbon Nanotube Field Effect Transistor as Non-Volatile Memory- A Review

Abstract

Carbon nanotubes (CNTs) are amongst the most explored one-dimensional nanostructures and have attracted tremendous interest from fundamental science and technological perspectives. Carbon nanotubes are one of the most inventive inventions in the field of nanotechnology, and they are the important materials in the nanoelectronics. Since its discovery in 1991, numerous research works have been drawn to it due to its enormous production. Carbon nanotubes (CNTs) have attracted much attention because of their unique electrical properties and their potential for a variety of applications. CNTs are also promising material as field effect transistors for future nanoelectronics and show hysteresis in the curve of the drain current versus gate voltage which makes CNTs possible for a non-volatile memory application. This paper highlighted on properties of CNTs and its applications as memory devices in electronics.

Introduction

Carbon Nanotubes (CNTs):
CNTs are hollow cylindrical structures made from rolled graphene sheets (a single atomic layer of carbon atoms arranged in a hexagonal lattice). They come in two main forms:

• Multiwalled Carbon Nanotubes (MWCNTs): multiple concentric cylinders.

• Single-walled Carbon Nanotubes (SWCNTs): a single cylindrical layer.

They were first observed by Sumio Iijima in 1991 (MWCNTs) and 1993 (SWCNTs). CNTs are categorized based on their atomic arrangement and chirality into zigzag, armchair, or chiral types, defined by their lattice vectors and indices (n,m).

Properties:

• Diameter: 1–2 nm; length: several micrometers.

• Can be metallic or semiconducting depending on structure.

• Extremely strong (100 times stronger than steel by weight), lightweight, highly thermally conductive, and electrically conductive with high current capacity.

• CNTs lack surface dangling bonds, differing from silicon, and can have improved gate insulators.

CNT-Based Field Effect Transistors (CNTFETs):

• First fabricated in 1998, where SWCNTs act as the channel between metal source and drain electrodes.

• CNTFETs exhibit high electrical conductivity, operational frequency, and can potentially replace silicon-based transistors in the future.

• Their direct bandgap (unlike silicon) allows for optoelectronic applications (light absorption and emission).

Memory Effects in CNTFETs:

• CNTFETs can exhibit charge storage and memory behavior similar to floating-gate MOSFET memories.

• Charge is stored in traps within the dielectric layer (like SiO2) between the CNT and substrate, causing threshold voltage shifts and hysteresis in transistor characteristics.

• Studies report memory retention times ranging from hours to days at room temperature.

• Improvements include enhanced hysteresis, stability, and retention through annealing and using CNTs as charge storage nodes or floating gates.

• CNT-based memory devices show promise for ultra-small, high-density, nonvolatile memory applications.

Conclusion

Based on the review in this paper, carbon nanotube field effect transistor has the potential to be used as the non-volatile memory in the field of nanotechnology. Generally, nanotubes are used as the channel between the source and the drain terminal of MOS structure but researchers are trying to use CNT as dielectric material in the gate stack which can be a replacement of high-k dielectric in the modern non-volatile memory device. It must be said that the excitement in this field arises due to the versatile properties of CNT. Nanotubes truly bridge the gap between the molecular and the macro-world, and are destined to be a star in future nanotechnology.

References

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Copyright © 2025 Gargi Chakraborty. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.