[Paleopsych] Plasmonic computer chips move closer
shovland at mindspring.com
Tue Mar 22 15:00:43 UTC 2005
Computer chips capable of speeding data around by rippling the electrons on
the surface of metal wires just got a step closer, researchers say.
Mark Brongersma, at Stanford University in Palo Alto, California, US has
found a new way to model the three-dimensional propagation of these ripples
- called plasmons - in two dimensions. He says the new model is much
simpler and more intuitive than existing simulations and will be crucial in
the design of plasmonic components for computer chips.
Plasmons travel at the speed of light and are created when light hits a
metal at a particular angle, causing waves to propagate through electrons
near the surface.
"Right now, the simulations are so complex that only a few groups in the
world can carry them out," says Brongersma. "The new model came out of a
desire for much simpler models."
Currently the biggest application for plasmons is in gold-coated glass
biosensors, which detect when particular proteins or DNA are present - the
bio-matter changes the angle at which light hitting the surface produces
the most intense plasmons.
But scientists would love to use plasmons to ferry data around computer
chips because they could operate at frequencies 100,000 times faster than
today's Pentium chips, without requiring thicker wiring.
Ordinary light waves can transmit data at similarly high frequencies, but
using photons to carry data across a computer chip is currently impossible.
This is because the size of the optical fibre that carries the light waves
must be about half the wavelength of the light, which is over twice the
thickness of the wires in modern chips.
"The big advantage of plasmons is that you can make the devices the same
size as electrical components but give them the speed of photons," says
Brongersma. Plasmon-carrying wires could also be made out of copper or
aluminium, like the interconnects on today's computer chips.
Brongersma points out that the speed of these interconnects has become a
key limiting factor. While transistors have become faster at switching as
manufacturers find ways to make them smaller and smaller, the wires that
carry the data are not getting any faster. "We need to find new ways to
connect transistors together," he says.
To develop the new, simpler model, Brongersma showed that the intensity
pattern of a plasmon travelling across the surface of a metal strip was the
same as for a light wave travelling through an optical fibre. He says this
indicates that traditional "ray-tracer" programs for modelling light waves
should work for plasmons too.
Such models are necessary if devices that generate and route multiple
plasmons are ever to be designed, Brongersma says. He will publish the work
in an upcoming issue of Optics Letters.
"Any advance that aids design is a good thing," says Harry Atwater of the
California Institute of Technology in Pasadena, US. But he warns that a
bigger hurdle to plasmon-based computer chips is finding plasmon sources
that are compatible with silicon. "The most important element is not the
design tools, it is having the ingenuity to know what to do with them," he
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