November 27, 2001. Copyright 2001. Graphic News. All rights reserved.

Molecular switches are Holy Grail of faster computers

LONDON, November 27, Graphic News: Scientists from Lucent TechnologiesÕ Bell Labs have built transistors -- the miniature electric switches that make up the brains of computers and other electronic devices -- a million times smaller than a grain of sand. The advance could play a key role in developing minuscule, super-fast, computer chips that use tiny amounts of power.

Transistors are similar to a basic light switch, which have two operating positions, on and off. This on/off, or binary function enables a computer to process information. The transistorÕs ÒonÓ stage, when current flows, is represented by a 1 and the ÒoffÓ state is represented by a 0. Specific sequences and patterns of 1s and 0s generated by multiple transistors represent letters, numbers, colours, and graphics.

Transistors consist of three terminals; the Òsource,Ó the Ògate,Ó and the Òdrain.Ó When a small positive voltage is applied to the gate negatively-charged electrons are then attracted to the gate and an amplified current flows between the source and the drain. In this state the transistor is on. A negative charge at the gate results in a build-up of electrons which blocks current flow and turns the transistor off. 

The speed at which the transistor can be turned on and off -- and hence the speed of the computer -- is dependent on the length of the ÒchannelÓ, the distance the electrons have to travel between the source, gate and drain.

It was at Bell Telephone Laboratories in 1948 that a three-man team designed the original transistor. John Bardeen, Walter Brattain and William Shockley later received the Nobel Prize in physics for their invention. Now, over 50 years later, another three-man Bell Labs team -- Hendrik Schon, Zhenan Bao and Hong Meng -- have built a single-molecule nanotransistor which opens the door to new levels of performance.

SchonÕs team used carbon-based semiconductor materials called thiols to produce what they call an organic transistor. Chemically, thiols are very similar to alcohol molecules, but with the oxygen atom replaced by a sulphur atom.

The transistors were assembled using a novel approach in which a single thiol molecule attached itself to an electrode made of gold. Because the channel length between the organic transistorÕs electrodes is so small -- between one and two nanometers (millionth of a millimetre) -- the transistorÕs output current and switching speed could be up to 10 times faster than todayÕs fastest processors. More than 100,000 of these devices would need to be stacked to achieve the thickness of a sheet of paper. 

The research from Bell Labs adds to a growing list of successful experiments in molecular electronics, including work by IBM, which in August announced a circuit made up of carbon atoms rolled together into tubes, and an Intel transistor just 30 nanometers in size and three atomic layers thick. 

ÒItÕs very hard to figure out how to electrically switch a molecule, and no one has ever made an electrical ÔgateÕ out of this type of molecule,Ó said Tom Theis, the director of physical sciences at IBMÕs research division. ÒIf thatÕs in fact whatÕs going on, then itÕs a very important step forward.Ó
/ENDS
Sources: Lucent Technologies, IBM, Reuters