Scientists invent single-molecule transistor

November 9, 2001 —

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

The "nanotransistor," which measures one-billionth of a meter, is more than 10 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 -- that of fabricating electrodes that are separated by only a few molecules and attaching electrical contacts to the tiny devices -- 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.

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 Corp., 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.

Bell Labs can be found online at http://www.bell-labs.com.

ITworld.com