Theos-Talk Archives (December 2001 Message tt00024)

Scientists Invent Single-Molecule Transistor

Thousands of so-called nanotransistors could be squeezed onto single chip, 
Bell Labs says.

David Legard, IDG News Service
Friday, November 09, 2001

A team of scientists at Lucent Technologies' Bell Labs has created a 
transistor contained within a single large molecule, the facility says. 

The "nanotransistor," which measures one-billionth of a meter, is more than 
ten times as small as any transistor previously made, Bell Labs said in a 
statement. It also does not require expensive clean-room technology to 
manufacture, and so potentially sets the stage for a new generation of faster 
and cheaper processing and memory chips in a few years' time.

The nanotransistor is not made of silicon, but from an organic (carbon-based) 
semiconductor material known as thiol. The principal problem with creating 
such a tiny transistor is of fabricating electrodes that are separated by 
only a few molecules and attaching electrical contacts to the tiny devices. 
This was overcome by enabling the transistor to effectively build itself from 
a liquid solution.

The Bell Labs scientists--one physicist and two chemists--carved a notch into 
a silicon wafer and deposited a layer of gold at the bottom to function as 
one of the transistor's three electrodes. They then dipped the wafer into a 
solution that contained a mixture of thiol molecules and some inert organic 
molecules, and as the solution evaporated from the wafer, a film exactly one 
molecule thick was left behind on the gold electrode. They then deposited 
another gold electrode on top of this film, while they built the transistor's 
third electrode on one side of the silicon notch, according to the statement.


Huge Capacity
Using two nanotransistors, the Bell Labs scientists built a voltage inverter, 
a standard electronic circuit module commonly used in computer chips that 
converts 0 to 1 or vice versa. With further development, it may be possible 
to create microprocessors and memory chips using nanotransistors, squeezing 
thousands of times as many transistors onto each chip than is possible today, 
Bell Labs said in the statement.

Silicon has been the basis of transistors since their invention at Bell Labs 
in 1947. Since then, improvement in transistor design has roughly followed 
Moore's law, which states that the maximum number of transistors on a chip 
will double every 18 to 24 months. But some scientists believe that 
continuing miniaturization of silicon-based integrated circuits will come to 
a halt within 10 years as fundamental physical limits are reached.

The other main approach to sidestepping these limitations has been developed 
by IBM, which is using carbon nanotubes, a tube-shaped molecule of carbon 
atoms that is 100,000 times thinner than a human hair, as the basis of 
computer circuits.