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:
Sound files suitable for radio broadcast and publication-
size images are available on the Internet at:
http://amesnews.arc.nasa.gov/audio/nanoconnsound/nanoconnsound.html
http://amesnews.arc.nasa.gov/releases/2003/03images/nanoconn/nanoconnpix.html
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