Carbon goes head-to-head with silicon

Scientists from Bell Labs have set the stage for a new class of inexpensive molecular electronics based on compounds of carbon with the creation of organic transistors with a single-molecule channel length.

Scientists from Lucent Technologies’ Bell Labs have created organic transistors with a single-molecule channel length, setting the stage for a new class of inexpensive and easily assembled molecular electronics based on compounds of carbon.

Bell Labs scientists Hendrik Schon, Zhenan Bao and Hong Meng have fabricated molecular-scale organic transistors, made out of compounds of carbon, which can reportedly rival silicon transistors in performance.

The Bell Labs team used the tiny organic transistors, which are roughly a million times smaller than a grain of sand, to build a voltage inverter – an electronic circuit that converts a ‘0’ to a ‘1’ and a standard component in all computer chips.

Researchers have long sought to create molecular-scale transistors, in which single molecules are responsible for the transistor action. The Bell Labs team built their transistors of gold and a class of organic semiconductor material known as thiols. The amplification and switching properties of the transistors are comparable to those of silicon transistors.

‘When we tested them, they behaved extremely well as both amplifiers and switches,’ said Schon, an experimental physicist and lead researcher.

Though still a prototype, the demonstration of a simple circuit is said to indicate that molecular-scale transistors could one day be used in computer microprocessors and memory chips, which could squeeze thousands of times as many transistors as are found in today’s circuits into the same amount of space.

The main challenges in making molecular-scale transistors are fabricating electrodes that are separated by only a few molecules and attaching electrical contacts to the tiny devices.

The Bell Labs researchers were able to overcome these hurdles by using a self-assembly technique and a design in which the electrodes were shared by many molecular-scale transistors.

‘We solved the contact problem by letting one layer of organic molecules self-assemble on one electrode first, and then placing the second electrode above it,’ said Bao, an organic chemist. ‘For the self assembly, we simply make a solution of the organic semiconductor, pour it on the base, and the molecules do the work of finding the electrodes and attaching themselves.’

The chemical self-assembly technique is said to be easy and relatively inexpensive and determines the transistor channel length.

The channel length of the Bell Labs molecular-scale transistors is 1 to 2 nanometers, less than a tenth the size of any channel that has been created.

‘Although there may be no practical applications for a decade, it could lead to a new paradigm in electronics,’ said Cherry Murray, Lucent’s senior vice president of physical sciences research. ‘Gaps remain in the theoretical understanding of these tiny devices, however, and they would need to be closed before industrial applications would be possible.’

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