Precursor to Tiniest Chip Is Developed
October 18, 2001
By KENNETH CHANG
In an advance that presages the tiniest of computer
circuitry possible, researchers at Lucent Technologies have
built a transistor in which the layer that switches
currents on and off is only one molecule thick.
Dr. J. Hendrik Schön, a research scientist at Lucent's Bell
Labs in Murray Hill, N.J., said the experiment proved that
transistors that worked exactly like those in current
computer chips could be built at the molecular scale.
"It shows what can be the ultimate limit for transistors,"
Dr. Schön said. The technology is years away from
commercial applications.
An article describing findings by Dr. Schön, Dr. Hong Meng
and Dr. Zhenan Bao, all of Bell Labs, appears in today's
issue of the journal Nature.
"It is really, really nice work that will influence the
field a lot," said Dr. James M. Tour, a professor of
chemistry at Rice University. "They hit on something really
big."
Transistors are essentially voltage-controlled switches. In
the off state, no current can flow through, which
represents a "0" in the binary language of computers. When
an electric field is applied from the side, from a third
terminal known as a gate electrode, the electronic
properties shift and current starts to flow: the on or "1"
position of the switch.
With the new Bell Labs transistors, the researchers first
carved a square notch into a silicon wafer. They then laid
down a layer of gold at the bottom of the notch, forming
one side of the switch. The wafer was then dipped in a
solution of carbon- based, stick-shaped molecules that
behave as semiconductors, with the ends of the molecules
designed to bond to gold.
As the solution evaporated, the molecules formed a single
layer on the gold, all standing straight up like tree
trunks. A second gold layer was then added on top for the
other side of the switch.
The vertical wall of the silicon notch acted as the gate
electrode, applying the electric current that turned
current on and off between the gold electrodes.
The layer of carbon-based molecules is less than one
ten-millionth of an inch thick, far thinner than the
equivalent structure in current silicon transistors. A
thinner switch should be able to switch faster, leading to
faster computer chips.
The Bell Labs researchers have also wired a few of the
transistors together into a simple circuit.
Current techniques of carving transistor circuits into
silicon are expected to run into fundamental physical
limits in 10 to 15 years that will stop further
miniaturization.
Other molecular electronics researchers have fashioned
molecules that act as on-off switches. Transistors, with
the additional gate electrode, also amplify the incoming
signal, which counters the effects of electrical resistance
as the signals pass through the circuit.
This year, two groups of researchers, one at I.B.M. the
other at Delft University of Technology in the Netherlands,
announced that they had built transistors and simple
circuits out of ultra-thin carbon cylinders known as
nanotubes. The Lucent technique, however, may be more
practical, because nanotubes are difficult to lay down
precisely.
"It's a step above what has ever been done in nanotubes,"
Dr. Tour said. "Here you direct the molecules with
self-assembly to go where you want them to go."
Dr. Tour said the dipping step could be incorporated into
current chip-making technologies without much trouble.
"They built all this upon a silicon platform," he said.
"This is the marriage you want."
While the switching layer in the prototype transistor is
only one molecule thick, it still contains several hundred
thousand molecules. Lucent officials hinted that further
advances were imminent as they work to shrink the number of
molecules in the switching layer.
"This is just the beginning of a revolution," said Dr.
Federico Capasso, vice president for physical research at
Bell Labs.
Shrinking transistors is not a solution by itself, said Dr.
R. Stanley Williams, director of quantum science at
Hewlett-Packard Laboratories in Palo Alto, Calif. If
trillions of molecule-size transistors could be made,
trying to wire them together could be an intractable mess.
http://www.nytimes.com/2001/10/18/science/18TRAN.html?ex=1004394494&ei=1&en=
bbd26de1e37f291e
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