Current top-down methods of chip production use electron beam lithography, an expensive process that involves etching silicon into smaller and smaller pieces. Such methods will eventually hit a limit at which further miniaturization would entail extreme expense.

"The current microelectronic industry will hit a wall in the near future," says Assistant Professor of Chemistry Hongkun Park.

Instead of taking large structures and cutting them into smaller pieces, however, some scientists, however, are taking the opposite approach. Using a bottom-up approach, they are focusing on taking extremely small units and combining them into working machines

In November, Science ran a special issue on the present reality and the possibilities of nanotechnology, the building of complex structures atom by atom. Possible applications include quantum cryptography, exotic new materials and, of course, miniature computers.

According to Lieber, using the bottom-up approach to make logical devices involves steps where the parts of a microchip are first fabricated and then arranged to form complex logical devices.

BF: Vacuum Tubes to Nanotubes

Making the basic units of a microchip in nanoscale is challenging in itself. The Lieber group has used nanowires made of silicon with added chemical impurities that allow the material to conduct some electricity.

Another top candidate for the building blocks of extremely small computers are carbon tubes two hundred nanometers across, called nanotubes.