Mass. -– Chemists
and engineers at Harvard University have made robust circuits from minuscule
nanowires that align themselves on a chip of glass during low-temperature
fabrication, creating rudimentary electronic devices that offer solid performance
without high-temperature production or high-priced silicon.
The researchers, led by chemist Charles M. Lieber
and engineer Donhee Ham, produced circuits at low temperature
by running a nanowire-laced solution over a glass substrate,
followed by regular photolithography to etch the pattern
of a circuit. Their merging of low-temperature fabrication
and nanowires in a high-performance electronic device
is described this week in the journal Nature.
"By using common, lightweight and low-cost materials
such as glass or even plastic as substrates, these
nanowire circuits could make computing devices ubiquitous,
allowing powerful electronics to permeate all aspects
of living," says Lieber, the Mark Hyman Jr. Professor
of Chemistry in Harvard's Faculty of Arts and Sciences. "Because
this technique can create a high-quality circuit at
low temperatures, it could be a technology that finally
decouples quality electronics from single crystal silicon
wafers, which are resilient during high-temperature
fabrication but also very expensive."
Lieber, Ham and colleagues used their technique to
produce nanowire-based logical inverters and ring oscillators,
which are inverters in series. The ring oscillator
devices, which are critical for virtually all digital
electronics, performed considerably better than comparable
ring oscillators produced at low temperatures using
organic semiconductors, achieving a speed roughly 20
times faster. The nanowire-derived ring oscillators
reached a speed of 11.7 megahertz, outpacing by a factor
of roughly 10,000 the excruciatingly slow performance
attained by other nanomaterial circuits.
"These nanowire circuits' performance was impressive," says
Ham, assistant professor of electrical engineering
in Harvard's Division of Engineering and Applied Sciences. "This
finding gives us confidence that we can ramp up these
elementary circuits to build more complex devices,
which is something we now plan to do."
Lieber and Ham say these functional nanowire circuits
demonstrate nanomaterials' potential in electronics
applications. The circuits could be used in devices
such as low-cost radio-frequency tags and fully integrated
high-refresh-rate displays, the scientists write in
Nature; on a larger scale, such circuits could provide
a foundation for more complex nanoelectronics. The
technique Lieber and Ham used to produce a nanowire-based
circuit on a glass substrate is also compatible with
other commonplace materials such as plastics, broadening
its potential applicability.
Lieber and Ham's co-authors are Robin S. Friedman
and Michael C. McAlpine in Harvard's Department of
Chemistry and Chemical Biology and David S. Ricketts
in Harvard's Division of Engineering and Applied Sciences.
Their work was supported by the Defense Advanced Research
Projects Agency, the National Science Foundation, and
the U.S. Air Force Office of Scientific Research.