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Towards the Single Molecule Transistor

Bell Labs' physicists Hendrik Schon and Shenan Bao have developed a field effect transistor (FET) combining both insulator and semiconductor layers within a single organic molecule.

The work builds on the development of a single-molecule transistorthat the two scientists built last November and is published in Applied Physics Letters.

"The molecules have two parts," said Schon. "In the conjugated part, there are mobile electrons. When you build up a series of molecules, the electrons interact and determine transport properties.It is similar to organic thin films."

The insulating part of the molecule is deposited on to a silicon substrate through precipitation out of a solution. A controlled chemical reaction grafts silane on to a silicon substrate, which also acts as the gate electrode. Pyrene units are attached to the insulating hydrocarbon silane structure, the pyrene acting as theconducting part of the molecule. A gold electrode for the drain is then thermally evaporated through a shadow mask.

Schon and Bao then assembled an insulating alkanethiol monolayercovering the top and side wall of the drain electrode. The source electrode was evaporated on top of this structure. Using this technique, Schon and Bao have succeeded in producing 2nm transistors.

"The combination of insulating and semiconducting parts could lead to true single-molecule transistors," said Schon. "We need now to develop a more complex molecular design and connect them to some kind of contact."

In tests at Bell Labs, Schon and Bao established a circuit with the transistors which ran for hours without any sign of degradation and the monolayers demonstrated stability up to 200 degrees C. Tests also achieved mobilities of 0.05cm2/Vs and on/off current ratios of more than 10,000.

This could eventually lead to transistors more than 100 times smaller than those produced using conventional CMOS processes, but Schon does not anticipate commercial development for a decade.

(C) 2002 EE Times.