Graphene-based transistors on the way?

The idea of replacing silicon with carbon to make computer chips is not new. However, using graphene -- a single layer of carbon atoms arranged in a honeycomb lattice -- wasn't feasible because it is not possible today to make wafers as big as ones made from silicon. But two researchers from Princeton University have found a very elegant solution to this problem. They've decided to put small crystals of graphene only in the active areas of the computer chip. Their graphene-based transistors are already '10 times faster than silicon transistors in moving electronic holes -- a key measure of speed.' This technique could be applied to wireless communication devices within a few years.

The idea of replacing silicon with carbon to make computer chips is not new. However, using graphene -- a single layer of carbon atoms arranged in a honeycomb lattice -- wasn't feasible because it is not possible today to make wafers as big as ones made from silicon. But two researchers from Princeton University have found a very elegant solution to this problem. They've decided to put small crystals of graphene only in the active areas of the computer chip. Their graphene-based transistors are already '10 times faster than silicon transistors in moving electronic holes -- a key measure of speed.' This technique could be applied to wireless communication devices within a few years.

Making transistors with graphene

You can see on the left an illustration showing their new technique. (Credit: Princeton University/Nano Letters) This bright idea of 'printing' only selected areas of a chip with graphene came to Stephen Chou, , professor of electrical engineering, and to Xiaogan Liang, a graduate student Xiaogan Liang in his Nanostructures Laboratory.

So Chou and the researchers in his lab developed high-performance working graphene transistors by using their new idea. "In their new method, the researchers make a special stamp consisting of an array of tiny flat-topped pillars, each one-tenth of a millimeter wide. They press the pillars against a block of graphite (pure carbon), cutting thin carbon sheets, which stick to the pillars. The stamp is then removed, peeling away a few atomic layers of graphene. Finally, the stamp is aligned with and pressed against a larger wafer, leaving the patches of graphene precisely where transistors will be built."

And is this possible to use this technique today? According to the researchers, the answer is yes. "The technique is like printing, Chou said. By repeating the process and using variously shaped stamps (the researchers also made strips instead of round pillars), all the active areas for transistors are covered with single crystals of graphene. 'Previously, scientists have been able to peel graphene sheets from graphite blocks, but they had no control over the size and location of the pieces when placing them on a surface,' Chou said."

So far, Chou and other members in his lab say their graphene-based transistors are 10 times faster than silicon-based ones.

For more information, this research work has been published in Nano Letters under the title "Graphene Transistors Fabricated via Transfer Printing in Device Active-Areas on Large Wafer" (Volume 7, Issue 12, Pages 3840-3844, November 14, 2007). Here is a link to the abstract which starts like this. "We demonstrate a method that uses the pillars on a stamp to cut and exfoliate graphene islands from a graphite and then uses transfer printing to place the islands from the stamp into the device active-areas on a substrate with a placement accuracy potentially in nanometers. The process can be repeated to cover all device active-areas over an entire wafer. We also report the transistors fabricated from the printed graphene."

Finally, do you agree with the researchers who think their new technique "could be applied to wireless communication devices within a few years"? Drop me a note whether you think it's possible or not.

Sources: Princeton University, Engineering School, December 18, 2007; and various websites

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