Posted: September 6, 2010

Elucidation of bandgap factors for graphene nanoelectronics

(Nanowerk News) The National Institute for Materials Science succeeded in elucidating the bandbap characteristics of graphene, which is key to realizing electronic devices using graphene, this being the thinnest high conductivity thin film (atomic film) on earth.
Miniaturization of semiconductor electronic devices is progressing, and the minimum processing dimensions of devices are expected to reach less than 10nm in the future. At the same time, the "limits of miniaturization" are being argued, as adequate current control is expected to be impossible with the conventional semiconductor materials when miniaturization exceeds a certain level. One method of solving this problem is considered to be electronic device using extremely thin conducting channels. As the material for such devices, the electrical conductivity of graphene has attracted wide attention.
In order to realize switching devices using new substances other than the conventional silicon semiconductors, formation of a bandgap in the electronic state of the thin film is desirable. While high expectations are placed on graphene as a next-generation electronic material, the lack of a bandgap in this ma, which is an atomic thin film with metallic characteristics, had been a problem. It had been pointed out theoretically that it should be possible to introduce a bandgap in graphene and obtain semiconductor characteristics by applying a perpendicular electrical field to two layers of graphene, and this had been shown to exist in optical research. However, in the most important electrical conductivity properties, this cannot be observed and is called the missing gap. Efforts to elucidate the basic cause of this missing gap had been debated worldwide.
In the present research, a perpendicular field was applied to graphene using a gate insulation film self-assembly method which we developed independently and makes it possible to apply an electrical field with the highest efficiency in the world. Using this approach, it is possible to apply a field to graphene with extremely good efficiency, enabling a clear investigation of device characteristics.
Although past research had concentrated only on extremely low temperatures, this was the first research that focused on the behavior of electrical conductivity from the temperature of liquid nitrogen to around room temperature. From these temperature characteristics, it was possible to discover unique features in conductors which possess a bandgap. Furthermore, we also discovered the physical factors necessary for the appearance of the missing gap. Based on these results, devices with bandgaps can be produced selectively, and great development in verification research on atomic devices enabling bandgap control is expected in the future. At present, we are fabricating basic logic devices using atomic devices which enable bandgap control and are carrying out research to reveal the latent properties of graphene.
These results were obtained in research by a group headed by Dr. Kazuhito Tsukagoshi (Principal Investigator) and Dr. Hisao Miyazaki (MANA Postdoct researcher), both of the NIMS International Center for Materials Nanoarchitectonics (MANA), in joint work with Associate Professor Akinobu Kanda and Associate Professor Susumu Okada of the University of Tsukuba and Dr. Minoru Otani, Group Leader of Energy Materials Simulation Research Group of the National Institute of Advanced Industrial Science and Technology (AIST).
This research was carried out as part of the research topic "High Operating Speed Organic Transistors by Nano Interface/Electronic State Control" in the research field "Establishment of Innovative Manufacturing Technology based on Nanoscience" in the Japan Science and Technology Agency Targeted Basic Research Program – Team Type Research (Core Research for Evolutional Science and Technology: CREST), and is scheduled for publication in the online edition of the American scientific journal Nano Letters in the near future.
Source: Research Center for Materials Nanoarchitectonics (MANA)