Shrinking silicon chips down to size.

Shrinking silicon chips down to size

The tinier the semiconductor transistor, the faster and less power-consuming it becomes. Some researchers, however, have wondered if there is a limit to the advantages of chip miniaturization, and have suggested that when transistor features get thinner than about 0.25 micron, unwanted "parasitic effects,' such as high resistance in the wrong places, would emerge.

Researchers at IBM Corp. in Yorktown Heights, N.Y., say they have allayed such worries by making some of the smallest silicon transistors ever fabricated and operating them at liquid-nitrogen temperatures (77 kelvins). While other scientists have made devices with individual parts in the 0.1-micron range, IBM's George A. Sai-Halasz and his colleagues are the first to scale down--in both the lateral and vertical dimensions--all the critical features to this size and smaller.

"At these dimensions we can pack 1 million of these things on a chip with no problem at all,' says Sai-Halasz. ". . . You could put a whole computer on not more than two or three chips.'

Operating the transistors at liquidnitrogen temperatures also enables the researchers to scale down the voltage needed to switch them on and off; this in turn reduces the power dissipated by the transistors. The low temperature also improves the performance of the devices, as measured by the transconductance, or current flow out of the device per unit change in voltage. The researchers will report in the October IEEE ELECTRON DEVICE LETTERS that the transconductance of their devices is 40 percent higher than that reported for other silicon devices operating at room temperature and is comparable to that of gallium arsenide devices (which have been pursued largely because they promised greater performance and faster speeds than their silicon counterparts).

Sai-Halasz says he's convinced that the only worthwhile semiconductor devices of small proportions will have to be cooled to low temperatures. But he doesn't view this as a technological barrier because the computer industry "is moving in that direction anyway.' By the time these kinds of tiny transistors can be put in mass production, he says, "liquid nitrogen will be no problem at all.' The next problem to be solved, he notes, is how to get rid of all the heat generated by extraordinarily densely packed chips.

Photo: With careful engineering, including the use of electron-beam lithography for delineating device features, IBM researchers have shown that high-performance, low-temperature silicon transistors with key parts smaller

than 0.1 micron can be fabricated.