Due to its extremely high carrier mobility and saturation velocity, developing the high-performance radio frequency (r. f.) graphene field effect transistors (FETs) is attracting enormous recent attention. A high-performance r.f. FET requires short gates in the channel. Up to now, the gate length (Lgate) has scaled down to 40 nm experimentally, and the measured maximum cut-off frequency (fT) is up to 300 GHz. Sometimes, the fT value does not always increase with the reduced Lgate in a transistor when Lgate approaches the size limit. It is necessary to know whether there is a saturation of fT with the reduced Lgate in graphene r. f. FETs. Besides this, another important issue of graphene r.f. FETs is whether there is an effective method to induce a drain current saturation in sub-10 nm scale.

Using quantum transport simulation, the Computational Materials Group led by Prof. Jing Lu at School of Physics, Peking University predict that fT still increases remarkably with the decreasing Lgate approximately in terms of 1/Lgate relation and reaches astonishing values as high as tens of THz. They also demonstrate a significant drain current saturation can be obtained if a band gap can be induced to the channel graphene, such as by applying a vertical external electric field to a BN/Graphene/BN sandwich structure (《NPG Asia Materials》4, e6(2012); http://www.nature.com/doifinder/ 10.1038/am.2012.10) or bilayer graphene. This study will provide important prediction and guidance for the performance limit of graphene r.f. applications.

This work has been published on Scientific Reports (Sub-10 nm Gate Length Graphene Transistors: Operating at Terahertz Frequencies with Current Saturation, Scientific Reports 3, 1314 (2013); http://www.nature.com/srep/2013/130219/srep01314/full/ srep01314). The first author of this paper is Jiaxin Zheng, a PhD student from Academy for Advanced Interdisciplinary Studies and School of Physics in Peking University. The collaborators include Prof. Gao Zhengxiang, Prof. Yu Dapeng, and Prof. Shi Junjie from School of Physics, Peking University, and Prof. Mei Wai-Ning from Department of Physics, University of Nebraska at Omaha.

The work was supported by the National 973 Projects, Program for New Century Excellent Talents in University of MOE of China, NSFC, and the State Key Laboratory for Artificial Microstructure and Mesoscopic Physics, Peking University.