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Scientists invent single-molecule transistor

Moore's Law takes another beating

Scientists at Lucent Technologies' Bell Labs have created a transistor within a single large molecule, the facility announced on Thursday.

The 'nanotransistor', which measures a billionth of a metre, is more than 10-times smaller than any transistor previously made, Bell Labs said in a statement. It does not require expensive clean-room technology to manufacture, 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 made from an organic (carbon-based) semiconductor material known as thiol, rather than silicon. 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.

A physicist and two chemists at Bell Labs 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 containing a mixture of thiol molecules and some inert organic molecules. As the solution evaporated on the wafer, a film exactly one molecule thick was left behind on the gold electrode. The scientists 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.

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 and vice versa. Bell Labs believes that, with further development, it may be possible to create microprocessors and memory chips using nanotransistors, squeezing thousands of times as many transistors on to each chip than is possible today.

Silicon has been the basis of transistors since their invention at Bell Labs in 1947. Since then, improvements 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 miniaturisation of silicon-based integrated circuits will come to a halt within 10 years as then material’s physical limits are reached.

IBM has developed an alternative approach to this difficulty 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.


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