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Michael Braukus
Headquarters, Washington               April 14, 2003
(Phone: 202/358-1979)

John Bluck
Ames Research Center, Moffett Field, Calif.
(Phone: 650/604-5026)

RELEASE: 03-136

NASA IMPROVES COMPUTERS WITH TINY CARBON TUBES ON SILICON 
CHIPS

     The life of the silicon chip industry may last 10 or 
more years longer, thanks to a new manufacturing process 
developed by NASA scientists.

The novel method, announced in the April 14 issue of the 
journal Applied Physics Letters, includes use of extremely 
tiny carbon 'nanotubes' instead of copper conductors to 
interconnect parts within integrated circuits (ICs). Carbon 
nanotubes are measured in nanometers, much smaller than 
today's components. A nanometer is roughly 10,000 times 
smaller than the width of an average human hair. ICs are 
very small groups of electronic components made on silicon 
wafers.

"NASA needs high-performance computing in small packages for 
future autonomous spacecraft," said Meyya Meyyappan, 
director of the Center for Nanotechnology at NASA's Ames 
Research Center (ARC), Moffett Field, Calif., coauthor of 
the article. "The bottom line is that computer chips with 
more layers and smaller components can do more for us. While 
we are working on carbon nanotube-based chips for long-term 
needs, we also are indirectly helping industry to keep 
silicon-based computer chips in use as long as possible," he 
said.

One advantage of using carbon nanotube interconnects within 
integrated circuits is that these interconnects have the 
ability to conduct very high currents, more than a million 
amperes of current in a one square centimeter area without 
any deterioration, which seems to be a problem with today's 
copper interconnects," said Jun Li, lead scientist of the 
team at ARC that developed the new process. "Also, there is 
no need to create deep, narrow trenches on silicon wafers in 
which to bury copper conductors, a step that also is 
becoming a problem as components are made smaller and 
smaller," Li added.

"Our process allows us to use the tiny carbon nanotubes to 
replace copper to interconnect network layers on silicon 
chips," Meyyappan said. "We think this new process may well 
help to sustain the Moore's Law growth curve."

Moore's Law stemmed from an observation made by computer 
chip pioneer Gordon Moore in 1964 that the number of 
transistors in a given area of an IC had doubled every year 
since its invention. Moore predicted the trend would 
continue at a rate of about 18 months between doublings. 
Continuing down this 'doubling' path is becoming 
increasingly difficult, according to Meyyappan.

"Roadblocks exist in several common technologies such as 
interconnects, lithography and others currently used to make 
the chips," he said. "However, I think our new process could 
be in use by industry for the next generation of ICs, 
removing some of these roadblocks," Meyyappan added.

"Using the new process, manufacturers will be able to add 
more cake-like layers of components to silicon chips to 
increase computer capability," Li said. Because copper's 
resistance to electricity flow increases greatly as the 
metal's dimensions decrease, there is a limit to how small 
copper conductors can be. In contrast, extremely tiny carbon 
nanotubes can substitute for copper conductors in smaller 
computer chip electronic configurations, because carbon 
nanotube electrical resistance is not high.

The new process includes 'growing' microscopic, whisker-like 
carbon nanotubes on the surface of a silicon wafer by means 
of a chemical process. Researchers deposit a layer of silica 
over the nanotubes grown on the chip to fill the spaces 
between the tubes. Then the surface is polished flat. 
Scientists can build more multiple, cake-like layers with 
vertical carbon nanotube 'wires' that can interconnect 
layers of electronics that make up the chip.

For more information about NASA nanotechnology on the 
Internet, visit:

http://www.ipt.arc.nasa.gov

Sound files suitable for radio broadcast and publication-
size images are available on the Internet at: 

http://amesnews.arc.nasa.gov/audio/nanoconnsound/nanoconnsou
nd.html

http://amesnews.arc.nasa.gov/releases/2003/03images/nanoconn
/nanoconnpix.html

For more information about NASA on the Internet, visit:

http://www.nasa.gov

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