IBM researchers in Zurich, Switzerland, have demonstrated a
single-molecule device capable of repeatedly storing and retrieving data.
Described in the Aug. 4 issue of nanotech journal Small Times, the device is
a surprisingly simple organic compound that can be set to high or low resistance
through electrical pulses. In the lab, it reliably retained its ability to
change states over many hours and more than 500 tests, which the researchers
described in the paper as "a remarkable result for a single-molecule system."
"Right now, we are concentrating on understanding the relationship between
the design of the molecular system and the electrical properties measured,"
researcher Heike Riel told ZDNet UK. "Our next steps are to investigate
the mechanism responsible for switching."
The molecule at the heart of the system, BPDN-DT, was designed by
professor James Tour and co-workers at Rice University in Houston and is one of
a class of compounds called Tour wires. Although it was specifically synthesized
to operate in this and other devices--it has also been used in a single molecule
transistor--there is still considerable debate as to how it works and what
characteristics any potential commercial application may have.
"The maximum switching speed depends very much on the mechanism which is used
for switching," Riel said. "The switching time is at least faster than 640
microseconds. However, we cannot give an upper limit yet." She said this would
depend on future investigations into how it worked and that tests done on a
similar molecule conclusively narrow the active area of the device down to a very specific area.
The experiment itself mounted the molecule between two gold electrodes that
could be adjusted to subpicometer accuracy. Although most of the testing took
place under extremely cold conditions, some results showed that the molecule
continued to switch states at room temperature--though, as the gold was then
much softer, it flowed and short-circuited after a few cycles.
At about 1.5 nanometers long, the molecule is less than a hundredth of the
size of current silicon memory elements. It is widely accepted in the industry
that current progress in silicon will become economically more difficult below
20nm, with fundamental physical limits being reached below 10nm. IBM says it
sees molecular computing as one way of pushing past this barrier, as well as
semiconducting wires, carbon nanotubes and spintronics.