Scientists develop microchip that is just one molecule thick

Pushing beyond current abilities, researchers at Lucent Technologies' Bell Labs have built a transistor that is one molecule thick, as well as tunable circuits wherein it is possible for them to modulate the flow of electricity through organic superconductors.

The technology might be the "ultimate limit for transistors" according to Dr. J. Hendrik Schon, a research scientist at Bell Labs. Moreover, despite being years away from commercial applications this technology foreshadows newer, smaller and even faster computer chips.

"They hit on something really big," Dr. James M. Tour, a professor of chemistry at Rice University, said about the discovery. "It is really, really nice work that will influence the field a lot."

So what exactly is a transistor? A transistor is essentially a switch controlled by voltage. In relation to computers, when no current can flow through the transistor it is said to be in the "off" state and this is represent by a '0' in binary language. On the other hand, when electricity can flow through, it is said to be on, represented by a '1' in binary language.

What the researchers at Bell Labs essentially did to molecularize the transistor is as follows: first they carved a square notch in a silicon wafer and then a layer of gold was put in the notch to form one side of the switch. The wafer, with the gold, was then dipped into a solution of carbon-based, stick-shaped molecules. These molecules act as semiconductors and are designed so that their ends bond to the gold. The solution, having evaporated, left a layer, which was a single molecule thick and standing perfectly straight up. Finally, a second layer of gold was placed on top to act as the other end of the switch, thereby completing the process.

To turn the switch on, all that needs to be done is to apply an electric current through the vertical wall (the side of the silicon notch).

After the completion of the process the transistor layer, composed of the carbon-based molecules, is less than one ten-millionth of an inch thick. This is far thinner than an equivalent structure made using current technologies. It is also important to note that a thinner switch can switch faster, thus creating a faster computer chip

The Bell Labs' discovery does not come alone, however, as already this year two groups have announced the construction of similar transistors. A team at IBM and another at Delft University of Technology in the Netherlands has built transistors and simple circuits out of nanotubes, ultra-thin carbon cylinders. However, the technique used by Bell Labs may be more sensible as nanotubes are very difficult to lay down precisely, a requirement for transistors.

"It's a step above what has ever been done in nanotubes," Dr. Tour said, "This is the marriage you want."

"This is just the beginning of a revolution," said Dr. Federico Capasso, vice president for physical research at Bell Labs. While shrinking transistors is not the solution, it is a critical step in creating newer, better computer chips.

The tunable circuit designed by Bell Labs is essentially a type of Josephson junction. A Josephson junction is basically a superconductor ring with a gap in it which is spanned by a thinner piece of superconductor. This in turn causes the electricity to flow more slowly through the ring than if the ring were made up entirely of the one superconductor.

The Bell Labs researchers essentially tuned the device by changing the voltage of current flowing through an electrode at the gap. The change in voltage caused a connected piece of organic material to change from an insulator, which slows electricity flow, to a superconductor, which allows electricity to flow perfectly.

These tunable junctions work by taking "advantage of the fact that it is possible to switch between an insulator and a superconductor just by changing a voltage," said Dr. J. Hendrik Schon, a Bell Labs researcher.

Not only is the discovery significant in the realm of circuits, but it also has scientific significance in that "the strength of superconductivity can . be varied by an electric field controlled by a bias voltage [making it] possible to study superconducting properties such as critical current and energy gap as a function of carrier density without changing temperature," according to J. T. Chen, a Professor of Physics at Wayne State University.

However, the application of this technology to making new kinds of circuits, such as superconducting circuits, which would be more powerful than conventional circuits, can not be overlooked.

The research, which was a collaborative effort of Dr. Schon, Chrisitan Kloc and Harold Y. Hwang Of Bell Laboratories and Bertram Batlogg of Bell Laboratories and the Swiss Federal Institute of Technology (ETH) was published the research in the April 13, 2001 issue of the journal Science.