High-frequency transmission line based on graphene

South Korean researchers have developed a graphene-based high-performance transmission line with a faster operating speed than those using existing metals. Published in the journal Science Advances, their breakthrough is expected to contribute greatly to high-speed semiconductor and communication devices.

Led by Professor Jae Eun Jang, scientists at the Daegu Gyeongbuk Institute of Science and Technology (DGIST) researched the high-frequency transmission characteristics of single-layer graphene and developed a high-performance, high-frequency transmission line that induced an increase of device concentration inside graphene. The results showed how their transmission line could replace the metal used in existing high-speed semiconductor processing.

Due to the high integration and high speed of semiconductor devices, the resistance of metal wire in which signals among devices are transmitted has increased dramatically, reaching the limit of permissible current density. To resolve this issue, carbon-based nanostructures such as graphene and carbon nanotube have drawn attention as next-generation materials.

Graphene has a hexagonal array of carbon, with very thin thickness of 0.3 nm, electric conductivity that is 100 times greater than copper and electron mobility that is 100 times faster than silicon. It has thus been suggested as an electronic material that can replace existing metals and semiconductor materials. However, pure graphene has low device concentration of 10¹² cm^-2 with thin structural characteristics, which results in too high resistance.

Prof Jang’s team sought to improve the high-frequency transmission characteristics of graphene by enhancing device concentration inside the graphene. By combining graphene and amorphous carbon, the team increased the device concentration of graphene and enhanced its electrical characteristics. The high-frequency transmission of increased graphene was -8 dB, which could be comparable to metal nanolines.

The team also proved that defects inside graphene decrease the high-frequency transmission of graphene and developed a new, stable doping technique that minimised internal defects. This doping technique increased the device concentration of graphene by 2 x 10¹³ cm^-2 and showed stable thermal properties and electrical characteristics.

The high-frequency graphene transmission line developed by Prof Jang’s research team displayed high signal transmission efficiency and stable operating characteristics, which can be applied to the metal wiring processing of the existing semiconductor industry as well as next-generation integrated circuits.

“Along with device technology, transmission line is a very important technology in the semiconductor research field,” Prof Jang said. “We have developed a core base technology that can enhance the high-frequency transmission of graphene that can be used as a next-generation transmission line. Thanks to the results of convergence research by experts in nano-engineering, electronic engineering and physics, we expect to use the graphene on high-frequency circuits such as MMIC and RFIC.”

Image caption: PhD candidate Jae-hoon Yang and Professor Jae Eun Jang in the DGIST Department of Information and Communication Engineering.

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