Researchers close in on faster circuit chips using exotic carbon material
- By William Jackson
- May 15, 2009
Government-funded research programs examining the puzzling properties of graphene, a highly conductive form of carbon, have taken steps toward creating practical integrated circuit chips with the exotic material.
In back-to-back issues of the journal Science, teams of government and academic researchers announced the creation of a new semiconductor using graphene and published results of studies that help explain why charges are carried so quickly across the material.
“There are still enormous challenges to really put it into products, but I think this really could play an important role,” said Jing Guo, an assistant professor at the University of Florida and part of the team that fabricated the new transistor.
The research was funded in part by the National Science Foundation, the National Institute of Standards and Technology and the Office of Naval Research, as well as by MARCHO MSD and Intel Corp.
For more than 40 years, Moore’s Law -- predicting that the density of transistors on integrated circuits and, therefore, the computing power of devices using those chips would double roughly every two years -- has been in force. But engineers are reaching the upper limits imposed by the properties of silicon from which most chips are made. Unless new materials are found to replace silicon, Moore’s Law could be repealed.
Graphene has held promise as one of these new materials since its isolation in 2004. The single layer of carbon atoms arranged in a hexagonal matrix for some reason lets charge-carrying particles behave as if they have no mass, more like a photon than an electron. The result is that even at room temperatures, electrons are more than 100 times more mobile than in silicon. This could mean that tiny graphene circuits could enable chips with significantly more memory and speed in a smaller area.
Researchers already have produced one of two basic types of transistor, the positive or p-type, using graphene. A team of scientists and engineers from Stanford University, the University of Florida and Lawrence Livermore National Laboratory announced in the May 8 issue of Science that they had succeeded in making an n-type, or negative transistor with the material. It was created with a nanometer-wide ribbon of graphene to which nitrogen atoms were added.
N-type transistors have added materials that increase the number of electrons available for carrying negative charges. P-types have material added to remove some electrons, increasing the ability to carry a positive charge.
Creation of an n-type graphene transistor demonstrates the ability to produce both of the basic building blocks of semiconductors. For commercial production the new semiconductors to become practical, however, the high cost of graphene would have to come down and techniques would have to be developed to put billions of nano-scale transistors on a single chip.
Work published in the May 15 issue of Science by researchers from the NIST and the Georgia Institute of Technology could help make the production of graphene in large quantities economical.
The team tracked the “massless electrons” that carry charges so efficiently, using a custom-built NIST scanning tunneling microscope. It produced a high-resolution map of the distribution of energy levels of within graphene when in high magnetic fields, shedding some light on the strange behavior of its electrons. It found that graphene layers are uncoupled from adjacent layers because they stack in different rotational orientations.
“This finding may point the way to manufacturing methods for making large, uniform batches of graphene for new carbon-based electronics,” NIST said.
William Jackson is a Maryland-based freelance writer.