I.B.M. Researchers Create - 06-11-2011, 10:51 AM
I.B.M. Researchers Create High-Speed Graphene Circuits
By JOHN MARKOFF
I.B.M. researchers said Thursday that they had designed high-speed circuits from graphene, an ultra-thin material that has a host of promising applications, from high-bandwidth communication to a new generation of low-cost smartphone and television displays.
The I.B.M. advance, which the researchers reported in the journal Science, is a circuit known as a broadband frequency mixer that was built on a wafer of silicon. Widely used in all kinds of communications products, the circuits shift signals from one frequency to another.
In the Science paper, the I.B.M. researchers describe a demonstration in which they deposited several layers of graphene on a silicon wafer, then created circuits based on graphene transistors and components known as inductors. They demonstrated frequency mixing up to speeds of 10 gigahertz.
In the past I.B.M. has created stand-alone graphene transistors, but not complete electronic circuits.
Scientists began making flakes of graphene, an atomic-scale lattice of carbon atoms, in the 1970s. They have gradually refined the process so they can now produce films of the material that are just a single atom thick. The film arranges itself in a hexagon-shaped array of carbon atoms and has the advantages of being flexible, transparent and inexpensive to manufacture.
But it is not yet a candidate to replace today’s CMOS transistors, the basis for the microprocessors and computer memories in consumer electronics systems. Graphene does not have the same physical properties as semiconducting materials and cannot be used to completely switch on and off in the way that logic transistors are meant to do.
That has not tempered the industry’s excitement over potential applications for the material. In Europe and Asia, government and corporate investments are running far in advance of those in the United States, said Phaedon Avouris, an I.B.M. chemical physicist who is a leader of the company’s research effort.
“Outside the U.S. there is a lot of interest,” he said.
Both the European Union and South Korea have recently started $1.5 billion efforts to build industrial-scale efforts using graphene as a next-generation display material, he said. Singapore has also recently started a major investment in the material.
I.B.M.’s research has been supported by a more modest effort financed by the Defense Advanced Research Projects Agency, the Pentagon office that supports futuristic science and technology. (Graphene is being explored as a substitute for materials like gallium arsenide, used in high-frequency military communications equipment.)
One promising application for graphene is in making new parts of the radio-frequency spectrum available for consumer electronics applications, said Richard Doherty, president of Envisioneering Inc., an industry consulting firm.
“It allows you to tame a spectrum that before was the wild, wild West,” he said. For example, it might make possible a new class of Wi-Fi-style communications gear for wireless applications, or allow set-top cable boxes to be redesigned to send and receive ever-larger amounts of high-resolution video and data.
Mr. Doherty added that display manufacturers were especially interested in graphene because the current wave of displays based on OLEDs, or organic light-emitting diodes, have limited lifespans.
Last year, researchers at Sungkyunkwan University in South Korea announced that they had scaled up a technique to make full-screen displays based on an approach to making graphene film pioneered at the University of Texas, Austin.
The promise of the low cost of the material could also push graphene into today’s conventional consumer electronics systems.
“In principle it can be made very cheap and it can be light-transparent,” Dr. Avouris said, “and so even if we don’t go for high frequency, I think it can revolutionize the price” of radio-frequency electronics.
He acknowledged that while I.B.M. was now able to build circuits from the material, it was still learning reliable ways to make large quantities of graphene film. It is now possible to heat a silicon carbide wafer to about 1,300 degrees Celsius (nearly 2,400 Fahrenheit), causing the silicon atoms on the surface to evaporate and the remaining carbon atoms to rearrange themselves into the hexagonal graphene shape.
But because of the cost of silicon carbide wafers, Dr. Avouris said, I.B.M. is looking for other ways to create graphene.
Dr. Avouris said that as an I.B.M. researcher, he was not certain what the giant computer maker might do to commercialize the technology. Currently I.B.M. is not a major supplier of military electronics products.
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