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Nano ''resonators'' form tiny logic gate
A
nanoscopic ''"resonator"'' that could
form the building blocks for of the
logic gates inside an electromechanical computer has been developed by
US researchers.
Sotiris Masmanidis
at the California Institute of Technology in Pasadena and colleagues
suggest that computers constructed from nanoscale electromechanical
components could be more efficient and robust than purely electronic
computers.
The
resonator consists of a piece of gallium arsenide crystal 4 micrometres
long, 0.8 micrometres wide and 0.2 micrometres deep, attached to a
base. One side of the crystal "beam" is doped to provide extra
electrons, while the other is doped so that it lacks them.
When
an alternating current (AC) voltage is applied across the post, an
electric field is formed across the centre of the bar. A piezoelectric
effect then kicks in, causing the gallium arsenide crystal to deform.
If the AC voltage has the right
frequency, the bar will resonate,
vibrating like a metal bar after being struck.
Minuscule charge
In
experiments, a voltage as low as 5 nanovolts - the equivalent of the
charge on a single electron - was sufficient to drive the device.
The
resonator can also be "tuned" by applying a direct current (DC)
voltage. The DC voltage causes what is known as the depletion region -
the highly-resistive area in the centre of the bar - to shift slightly
towards the top or the bottom of the bar.
Since
it is this resistive region that is sensitive to the piezoelectric
effect, shifting it changes how the bar vibrates in response to the AC
voltage. The DC voltage can ensure the resonator responds to the
desired frequency or be used to turn it on and off.
The
researchers say such resonators could ultimately be used to make
nanoscopic logic devices. To demonstrate this, they took two bars and
touched their tips at right angles so that they formed an "L".
Crude gate
When
they ran an alternating current through either bar, the entire device
resonated at a particular frequency. When they ran current through
both, however, the vibrations cancelled each other out. The device
therefore functions like a crude logic gate. The researchers relied on
an optical interferometer to detect the resonance of both components.
Miles Blencowe,
a physicist at Dartmouth College in Hanover, New Hampshire, US, says
that in theory such a logic gate could be much more efficient than one
made from electronic components, because it would require less energy
and should waste less heat. It might also be more robust, he says.
But
to realise this goal, Blencowe says the next step is to figure out how
to turn the high-frequency signals from each resonator back into an
electromagnetic signal so that it can be fed into another device,
forming a larger logical circuit.Journal reference: Science (vol.317, p.780)