An Improved Carbon Nanotube Semiconductor

3D Diagram of the Carbon Nanotube Electronic Device and Its Scanning Electron Microscope (SEM) Image

Professor Yang-Kyu Choi and his research team of the School of Electrical Engineering at KAIST collaborated with Professor Sung-Jin Choi of Kookmin University to develop a large-scale carbon nanotube semiconductor by using a 3-D fin-gate structure with carbon nanotubes on its top.

Dong Il Lee, a postdoctoral researcher at KAIST’s Electrical Engineering School, participated in this study as the first author. It was published in ACS Nano on November 10, 2016, and was entitled “Three-Dimensional Fin-Structured Semiconducting Carbon Nanotube Network Transistor.”

A semiconductor made with carbon nanotubes operates faster than a silicon semiconductor and requires less energy, yielding higher performance.

Most electronic equipment and devices, however, use silicon semiconductors because it is difficult to fabricate highly purified and densely packed semiconductors with carbon nanotubes (CNTs).

To date, the performance of CNTs was limited due to their low density. Their purity was also low, so it was impossible to make products that had a constant yield on a large-surface wafer or substrate. These characteristics made the mass production of semiconducting CNTs difficult.

To solve these difficulties, the research team used a 3-D fin-gate to vapor-deposit carbon nanotubes on its top. They developed a semiconductor that had a high current density with a width less than 50 nm.

The three-dimensional fin structure was able to vapor-deposit 600 carbon nanotubes per micrometer. This structure could have 20 times more nanotubes than the two dimensional structure, which could only vapor-deposit thirty in the same 1 micrometer width.

In addition, the research team used semi-conductive carbon nanotubes having a purity rating higher than 99.9% from a previous study to obtain a high yield semiconductor. 

The semiconductor from the research group has a high current density even with a width less than 50 μm. The new semiconductor is expected to be five times faster than a silicon-based semiconductor and will require five times less electricity during operation.

Furthermore, the new semiconductor can be made by or will be compatible with the equipment for producing silicon-based semiconductors, so there will be no additional costs.

Researcher Lee said, “As a next generation semiconductor, the carbon nanotube semiconductor will have better performance, and its effectiveness will be higher.” He also added, “Hopefully, the new semiconductor will replace the silicon-based semiconductors in ten years.”

This study received support from the Center for Integrated Smart Sensors funded by the Ministry of Science, ICT & Future Planning of Korea as the Global Frontier Project, and from the CMOS (Complementary Metal-Oxide-Semiconductor) THz Technology Convergence Center of the Pioneer Research Center Program sponsored by the National Research Foundation of Korea.

3D Transistor Device on an 8-inch Base and the SEM Image of Its Cross Section