NEWS OF THE WEEK NANOELECTRONICS
CARBON-BASED FETs BEST SILICON
Nanotube
New design helps nanotube devices move ahead of industry standard
C
ARBON-NANOTUBE-BASED
transistors can outperform transistors made from sili con, according to a new IBM study. The finding strengthens the position of carbon nanotubes as the leading contender to re place silicon in electronic devices when the size of silicon-based cir cuits can no longer be reduced. Advances in microelectronics, lithography, and relatedfieldshave helped shrink electronic circuits at a fast rate for the past two de cades. But experts contend that such reductions cannot continue much longer due to limitations imposed by fundamental materi als properties. So researchers are investigating new materials and methods for making circuits with nanometer-scale dimensions. "Carbon nanotubes are already the top candidate to replace sili con when current chip features just can't be made any smaller— a barrier expected to be reached in 10 to 15 years," says Phaedon Avouris, manager of nanoscale science and technology at IBM's T. J. Watson Research Center, %rktown Heights, Ν. Υ Ύεί even with carbon-nanotube-based electronics poised to make a big splash, silicon circuitry has main tained a comfortable, if shrink ing, lead over the competition. But now carbon nanotubes have pulled ahead in the per formance race. The latest IBM carbon-nanotube field-effect transistors (FETs) outperform transistors found in today's com mercially available devices and even score higher than prototype advanced silicon-based transis tors. Avouris and IBM cowork ers Shalom J. Wind, Joerg ApHTTP://PUBS.ACS.ORG/CEN
penzeller, Richard Martel, and Vincent Derycke report that their new carbon-nanotube FETs work better in terms of the switching rate and the amount of current they can carry per width of conductor [Appl. Phys. Lett., 80, 3817(2002)}. The new IBM devices differ from carbon-nanotube FETs demonstrated previously at IBM and elsewhere in several impor tant ways, Avouris explains. The latest round of FETs do not use a silicon wafer that supports the de vice as one of the electrodes. In stead, the FETs are designed with a top gate—an electrode situated above the nanotube that controls theflowofelectricity through the device.The design enables all FETs in contact with the silicon wafer to be switched individually—an advantage that opens the door
Silicon dioxide Silicon wafer Gate oxide P E R F O R M A N C E Carbon-nanotube field-effect transistors (FETs), with a design that places a gate (electrode) above a carbon nanotube and includes very thin insulating layers, outperform FETs made from silicon.
to increasing device complexity In addition, the switching volt age has been decreased by rough ly one order of magnitude relative to older designs. And both p-type (positive-charge carrying) and ntype devices were demonstrated by the IBM group, further in creasing the usefulness of the new circuit building blocks. "The work shows that carbonnanotube transistors can be very competitive with silicon, and therefore the effort in nanotube research is certainly worthwhile," Avouris notes. —MITCH JACOBY
CONGRESS
Senate Okays Fast-Track Trade Bill trade bill passed by the Senate late last month will be tough to reconcile with the version the House passed last De cember, but industry associations are hoping it will be signed by President George W. Bush before the July congressional recess. The bill expands trade preferences to four Andean nations and includes trade adjustment assistance to aid workers who lose jobs be cause of expanded trade. But its core provi sion gives the President fast-track negotiating authority for making trade agreements, which can then only be voted up or down by Congress. The fate of the bill is unclear because of a Senate amendment that allows any senator to reopen a treaty to remove any provision that changes U.S. trade remedy laws, such as anti
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dumping measures or countervailing duties. The Bush Administration has threatened to ve to any bill containing this provision, but House and Senate negotiators seem certain the measure will be dropped. As the largest U.S. exporting industry, the chemical industry has a big stake in expediting trade agreements. Removal of foreign tariffs on chemical products is important to the in dustry, and the lack of negotiating power has left the U.S. out of some recent international deals. "We are extremely pleased at the Sen ate approval of the bill," an American Chem istry Council spokesman tells C&EN. "We are calling for quick action by the conference com mittee to reconcile the two bills and recom mend that the final report be sent to the Presi dent for signing by July4."-DAVID HANSON
C&EN
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