Tiny structures molded in capillaries.

With the size of microelectronics seemingly shrinking by the month, scientists must search for better ways of fabricating tiny circuits, machine parts, manipulators, and optical devices.

Photolithography - a technique that uses lasers and light-sensitive chemicals to etch surfaces - has satisfied existing needs for the most part, particularly where metal, glass, and silicon come into play.

Plastics present other difficulties, especially as conductive polymers increasingly find their way into the microelectronic domain. To facilitate the use of polymers in the land of Lilliputian machinery, Enoch Kim, Younan Xia, and George M. Whitesides, all chemists at Harvard University, propose a new method for building polymer microstructures and etching plastic surfaces.

Their technique, reported in the Aug. 17 Nature, allows them to cast tiny features in microscopic molds, filling them with liquid polymers by way of capillary action. Called MIMIC - for micromolding in capillaries - the new method employs a flexible master mold laced with a network of channels that forms patterns when placed on a substrate, the scientists explain.

No method exists for filling such narrow channels directly, the researchers note. However, when thin liquid polymer seeps into the tiny canals, capillary action pulls the plastic juice into the network.

Once the polymer has set and cured, hardening into a malleable plastic, the researchers can remove the patterned microstructure from the master and reuse the mold. The result is a layered, textured surface on which stand distinct, three-dimensional features.

"In this MIMIC process, we're doing the same type of thing that people do with photolithography," Kim says, "except that we can do this in a chemistry lab without any elaborate lithographic instruments."

"This process is much simpler and less expensive than traditional photolithography," he adds. For instance, photolithography requires two steps to form and pattern a film, whereas MIMIC requires only one - since forming and patterning a polymer film occur simultaneously.

Unlike standard lithographic methods, MIMIC permits a manufacturer to retain the master mold and make hundreds of subsequent copies, Kim notes. In addition, the technique works on many kinds of surfaces and materials, not just the flat films to which most lithographic techniques have traditionally been limited.

"The process is quite flexible," Kim says. Moreover, the ability to reproduce three-dimensional patterns and films of varying thickness distinguishes MIMIC from standard microlithography.

"Whitesides' recent work is very important," says Calvin F. Quate, a physicist at Stanford University. "I suspect that he's onto something. He'll probably find an interesting application for this technique."

As part of MIMIC's development, the research team will apply the patterning technique to other types of materials, observing both the method's advantages and limitations - particularly for patterning conducting polymer micro-circuits and tiny optical systems.

Though in an early stage of development, MIMIC might one day find its way into the manufacture of computer chips or polymer diodes, Kim says.

"But that's still a long way off," he notes. "This process is still in its infancy."