Transistor sports molecule-thin layer

By Eric Smalley, Technology Research News

Editor's note: this research has been withdrawn by the scientists.

It's going to be a long time before anyone builds a computer with components made out of individual molecules. The big obstacle is figuring out how to wire billions of molecules together without having to connect them one by one.

Short of that lofty goal, however, making parts of components only one molecule thick could make for faster computers.

Researchers at Lucent Technologies' Bell Labs have made a transistor that uses a single layer of molecules as a semiconductor. "We have demonstrated that such tiny devices can act as a transistor [to] switch and amplify signals," said Hendrik Schön, a physicist at Bell Labs. The researchers also connected two of the transistors to form an inverter, which reverses a signal.

Transistors are microscopic electronic switches that channel electrical current; there are millions of them on computer processor and memory chips. The most common way to make faster chips is to use smaller transistors, shortening the path electrons have to travel to switch the devices on and off.

The Bell Labs' transistors are not especially small. While the semiconductor is only a molecule thick, each transistor uses 1,000 of the semiconducting molecules and is about 800 nanometers wide, said Schön. But they set the stage for smaller transistors and are a step toward the ultimate goal of making a transistor from a single molecule.

"The [semiconductor layer] of the device can be as small as a molecule, about 1 nanometer," said Schön. "This is more than a factor of a hundred smaller than state-of-the-art silicon devices in, for example, a Pentium chip."

Transistors usually have five parts: a semiconducting channel that carries the flow of electrons, a source electrode that puts electrons into the channel, a drain electrode that takes electrons out of the channel, a gate electrode that turns the flow on and off, and an insulator that separates the gate electrode and the channel.

In field-effect transistors like the Bell Labs' device, when current is applied to the gate electrode it produces an electric field that lowers the resistance of the semiconducting channel, causing current to flow from the source electrode through the channel to the drain electrode. Computers use this flow and absence of flow to represent the ones and zeros of binary logic.

The semiconductor portion of the Bell Labs' device is also organic, or carbon-based, rather than silicon. This means the layer can be formed using simple, room-temperature chemical processes and does not require the expensive facilities and equipment ordinarily used to make computer chips, said Schön.

The other components of the Bell Labs' transistor were made from more traditional computer chip materials: silicon for the gate electrode, silicon oxide for the insulator, and metal for the source and drain electrodes.

The researchers are also working toward replacing these with organic -- and smaller -- components that assemble chemically, said Schön. "We want to make use of more complex schemes of self-assembly. For example, not only defining the active material but also [making the] insulator and contacts by similar techniques," he said.

Other researchers have built the insulator portion of field-effect transistors using self-assembled single-molecule layers. Building all of the components of the transistor out of organic materials would also make it flexible, which means it could be used to make electronic devices on sheets of plastic.

The researchers' long-term goal is to make an entire transistor out of a single molecule, said Schön. "[One] goal is to design and synthesize more complex molecules, which combine the different transistor functionalities -- semiconductor, insulator, electrodes -- on a single molecule," he said.

What the researchers have done so far "is a very nice science result," said Mark Reed, a professor of engineering and applied science at Yale University. There's a lot of work to be done before the layers can be used in practical transistors, however.

It will be at least ten years before manufacturers can produce transistors using single-molecule semiconductor layers, said Schön.

Schön's research colleagues were Hong Meng and Zhenan Bao. They published the research in the October 18, 2001 issue of the journal Nature. The research was funded by Lucent Technologies.

Timeline:   >10 years
Funding:   Corporate
TRN Categories:   Semiconductors; Integrated Circuits; Materials Science and Engineering
Story Type:   News
Related Elements:  Technical paper, "Self-Assembles Monolayer Organic Field-Effect Transistors," Nature, October 18, 2001


October 24, 2001

Page One

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Transistor sports molecule-thin layer

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