Molecular Self-Assembly

Computerworld - Someday, computer chips will be grown, not made.

The concept of nanotechnology—that is, the manufacture of preposterously small objects—is at least familiar to most, although the scales involved continue to boggle the mind (a pinhead is about 1 million nanometers wide). It's easy to see why such extreme miniaturization interests semiconductor makers: Feeding the beast called Moore's Law grows more difficult with every generation of chips.

A number of companies are betting that the best way to operate in this nanoscale world is via "molecular self-assembly," in which circuits literally grow themselves. IBM, Texas Instruments Inc., Fujitsu Ltd. and Hewlett-Packard Co. are focusing on incrementally self-assembled components that can be integrated with conventional silicon-based chips. Meanwhile, start-ups such as ZettaCore Inc. and Cambrios Technologies Corp. aim to eliminate silicon completely by building entire semiconductors from molecules.

But, experts caution, the race is not a sprint but a marathon whose finish line is 20 years off at least.

Researchers have already shown that it's possible to integrate self-assembly with conventional semiconductor-manufacturing techniques—meaning chips that are at least partially self-assembled may be found in commercially available computers in five to seven years, says Jack Uldrich, president of The NanoVeritas Group in St. Paul, Minn., and co-author of The Next Big Thing Is Really Small (Crown Business, 2003).

Natural Patterns

Self-assembly—the tendency of certain structures to fall naturally into patterns—is one of nature's most common occurrences. On a grand scale, for example, wind direction, temperature and moisture in the air result in predictable types of storms.

Now think smaller—much smaller. Certain molecules combine without guidance in predictable ways. "Some molecules recognize each other and find natural low-energy states," says W. Grant McGimpsey, a biology professor and director of the Bioengineering Institute at Worcester Polytechnic Institute in Massachusetts.

A common example—and one that's expected to play a prominent role in chip making—is the SAM, or self-assembling monolayer. When a substrate and molecules with long carbon chains are combined under the right conditions, SAMs self-assemble.

"The neat thing about SAMs is they're very well ordered," McGimpsey says. A field of these SAMs protrudes from the substrate at a well-defined angle—like a small patch of thick, well-tended grass—and can perform several duties, such as improving conductivity or increasing surface area. Such order, McGimpsey says, "means predictability of structure, and thus of properties."

To date, the management of self-assembled molecules that could be applied to semiconductors is limited to a few basic structures. However, researchers believe that's a benefit, not a drawback.

Because of the high cost of tooling up, process change in the semiconductor industry is slow. Thus, self-assembly is sure to make its way into integrated circuits only gradually. Early applications will be simple and unglamorous.