Big Blue's Unlikely Speedster


IBM set a new marker on Feb. 25 when it unveiled the fastest silicon-based chip to date at a semiconductor industry conference in San Mateo, Calif. Big Blue's new marvel zips along at a blazing 110 gigahertz (GHz), thanks to transistors that can switch on or off 285 billion times every second -- far more than the 200 billion cycles per second that had been considered the red-line maximum for silicon transistors.

Now here's the big surprise: The key to these fantastic speeds isn't the usual smaller transistors and thinner circuit lines, which have long been the main drivers of ever-increasing chip speed. In fact, this record-setting chip has relatively fat 0.13-micron-wide transistors and lines -- sizes that date back to the late 1990s.

SMOOTH CHEMICAL PAIRING. Instead of smaller lines, the chip's blistering speed stems from a new silicon-and-germanium recipe. IBM began developing silicon-germanium (SiGe) materials two decades ago, when industry pundits were warning that pure-silicon chips would top out in the 1990s. Leading the SiGe charge was Bernard S. Meyerson, now an IBM Fellow and a research vice-president.

Normally, silicon and germanium won't work together. Their crystalline structures don't match up, and that produces huge collections of microscopic defects. But Meyerson's team found a way to combine silicon and germanium without creating problems.

IBM's first SiGe chip appeared in 1989, with transistors switching on or off 75 billion times a second. By 1994, SiGe transistor speeds had increased to almost 120 billion cycles a second. "People were telling us we couldn't go any further," says Senior Engineer Seshu Subbanna, who led the chip's development team at IBM Microelectronics in East Fishkill, N.Y. But IBM proved the doubters wrong. Refinements in the chipmaking process have improved Big Blue's ability to control the composition of SiGe layers and reduce their thickness -- both keys to the new speed champ.

The best part: Still faster chips could emerge when IBM gets around to shrinking line widths to 0.1 microns or below, now the cutting edge of semiconductor engineering. "We're very optimistic about future performance improvements," says Subbanna.

FAST SELLER. Since the late '90s, SiGe chips have become hot sellers in such telecom markets as mobile phones and, in particular, high-speed networking equipment. Sales figures for 2001 tell a trend-bucking story. While total chip sales plunged more than 30%, easily the largest-ever decline, Big Blue's SiGe sales soared 86%, to $260 million, according to market researcher IC Insights. And lots more growth lies ahead. By 2006, predicts IC Insights, worldwide SiGe sales will jump to $2.7 billion, up from last year's total of $320 million.

Silicon germanium has two chief rivals for superfast switching jobs that plain silicon can't handle -- gallium arsenide and indium phosphide. Until now, gallium chips had a slim edge in speed, and indium was way out in front. But even before IBM announced its latest breakthrough, IC Insights had predicted that SiGe could steal up to a quarter of gallium arsenide's market share by 2006.

Now, says IBM's Subbanna, indium phosphide also will be feeling SiGe's heat. "There's no reason to look at anything else but SiGe -- except for semiconductor lasers and light-emitting diodes," Subbanna crows. While silicon isn't a great transmitter of light, looks like Big Blue's new chip recipe could have some flash elsewhere. By Otis Port in New York


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