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01 October 2002

Wired molecules allow for flexible computers

Ithaca, N.Y. - How would you like a computer that is smaller, cheaper, and more flexible?

That is what a team of researchers from Cornell University will now work on after they received a $1.6 million grant. Officially, the project is to investigate "inorganic/organic interfaces."

In simpler language, the problem is: How do you connect wires to "organic" transistors? Organic here doesn't necessarily mean "living," however. Organic chemistry is the study of molecules built around chains of carbon and hydrogen atoms.

A $1.3 million, four-year grant from the National Science Foundation and $300,000 from Semiconductor Research Corp., a consortium of electronics manufacturers, helped fund the project. James R. Engstrom, Cornell associate professor of chemical engineering, is principal investigator on the project.

Organic semiconductors are drawing wide interest as a way to make very cheap electronic devices, perhaps even devices in which single molecules can act as switches. Currently, popular materials for making organic semiconductors are sexithiophene, made up of six five-sided groupings of carbons, and pentacene, made up of five six-sided rings.

In such molecules, some electrons are free to jump from one ring to another, making it possible to use the materials as transistors. Some organic semiconductors also emit light, making them useful as light-emitting diodes (LEDs) or in lasers. Organic LEDs are already in use in some cell phones and handheld video games.

These and other semiconducting organic molecules can assemble in long chains or polymers, which are the basis of plastics, so they can see use in inexpensive devices such as smart cards. Such devices can work very cheaply using "wet chemistry" approaches rather than expensive nanofabrication equipment.

Organics can form tough, flexible thin films and perhaps someday print onto fabric or paper. They also offer a promising approach to computing at the molecular level, where single molecules act as transistors.

However, as these devices grow smaller, connections to them become more difficult. When metals come in contact with organics, metal atoms tend to diffuse into the organic material, muddying up the contact. "Currently, you evaporate the metal onto the organic and cross your fingers," Engstrom said. He described the problem as one of making "molecular solder."

Under the new grant, the Cornell researchers will study in detail the chemistry of the bond formed when organic films are deposited on metals (or in some cases insulators) and, most importantly, the inverse: where metals are deposited on the organic.

Their approach involves "self-assembly," where a metal or insulating substrate masks to form a pattern, such as the pattern of wires to which circuit elements connect, and a film of organic material deposits on the unmasked areas.