Following the oil crises of the '70s, automotive engineers hot on the trail of fuel-efficient technology probably ignored the effects their increasingly compressed car designs had on the interaction of the families crammed inside. However, some contemporary scientists are worried about the effects of confinement -- on electrons -- as the sizes of semiconductor devices shrink ever smaller.

Obviously, chips cannot process more unless the transistors that drive them become smaller and faster. As ever-smaller transistors are "stuffed" into tinier compartments, experts wonder, will the close quarters change the essential nature of the components? Will properties like conductivity, for instance, remain the same no matter how small and compacted silicon chips get?

While it is exceedingly difficult to test properties in tiny chips themselves, physicist John Lipa and a team of scientists at Stanford and the Jet Propulsion Laboratory have developed an easier model for studying what lies ahead. Their experiment aboard the space shuttle Columbia uses helium atoms as stand-ins for electrons, and measures their properties as the conditions of confinement change.

Lipa's testbed -- called the Confined Helium Experiment, or CHeX -- is, like the car metaphor, a model for studying confinement. "It's like looking through a microscope," says Lipa of the way the unique properties of helium allow him and his team to examine atomic-scale phenomena. Helium is easy to manipulate at extremely low temperatures. Researchers can squeeze these atoms into an almost two-dimensional state with a comparatively big, easy-to-use measuring apparatus.

Schematic drawing of the CHeX apparatus (click to view larger, with explanatory labels)

The device itself sure doesn't look like a microscope. Around 400 silicon wafers are stacked in a cage. The 50-micron gaps between them -- about twice the width of a human hair -- are flooded with liquid helium near absolute zero. Heat is added. The microgravity environment of the space shuttle, meanwhile, eliminates pressure variations so that thermometers can measure the temperature change accurately to a billionth of a degree. If the added heat changes the temperature in the same manner as it does when the helium has more space, the confinement factor is negligible, and transistor-makers can breathe more easily as they go about trying to create faster, smaller silicon-based chips. If, on the other hand, a different relationship results -- and the confinement factor is significant -- this may signal the end of the silicon-based chip party. New technologies will need to be developed -- fast.

Although the final effect of confinement on helium has yet to be determined, Lipa says his preliminary runs indicate things "are a bit worse than expected. The confinement effect is bigger; it's hard to say how much just yet." Does this mean silicon chips have gotten as small as they can get? "It's going to take us a while to determine what it will mean in the Valley here," he concludes.

Although CHeX may be of use to chipmakers, it's valueless to automotive engineers trying to pinch just one more mile-per-gallon out of runt cars. They are going to have to find out some other way to discover just how much confinement a family can stand during a hot summer outing.

-- Louis Johns