An Optimistic View on Overcoming Limits

The first trend is the straightforward observation that progress in information technology continues at an ever increasing pace. This might seem obvious, he said, but most technology areas have rapidly improved and then reached a point of maturity and growth levels off. Even for microprocessors and computers we are near that point of maturity, although its exact position is unknown.

Indeed, there is some doubt in the semiconductor industry that its pace of growth can continue. Historically, about 50 percent of its improvements have been made through better yield per wafer, finer lithography, and other scaling techniques that reduce size and produce better electrical behavior. He showed evidence, however, that the pace of lithography improvements in the past few years has been faster than ever before.

He then turned to the transistor and a representation of the gate dielectric mentioned by Dr. Spencer. He noted that the transistor is now only about a dozen atomic diameters thick, and it is not clear how to reduce that thickness further than one-half of its current dimension. “So there are real fundamental atomic limits you approach,” he said. “That may make you wonder, why am I so optimistic?” He answered his own question by suggesting that improvements will come from other directions, supplementing the lithography and other aspects of scaling he had mentioned. “Physicists are famous for telling us what they cannot do and then coming back and doing something about it.”

Factors That Improve Performance

He illustrated his point with a chart where every figure represented a factor that improves performance at the same feature size (Figure 9). The challenge is that such improvements are one-time effects that must be followed by something else. Nonetheless, materials science has provided many such effects, such as introducing copper to interconnect the substrates of the chip; dielectrics that improve performance through the wires; and silicon on insulator that improves the circuitry within it. Silicon germanium is an alternative technology that does not replace CMOS but it does allow you to build mixed-signal processors at very high frequencies that can handle digital and analog circuitry together. He showed the relevance of this technology to Dr. Cerf’s comment that the communications industry’s urgent need is to make the translations from huge fiber backbones to routers and other components that can convert optical to electrical signals.

He then offered another illustration of how speed can be increased despite the physical challenges. He showed a picture of a friend holding the first experimental gigahertz processor on a wafer. Just three years ago a gigahertz was three times the speed of any commercially available processor and yet it was produced on a 300-megahertz processor line. This was done not by semiconductor power but by redesigning the data flows to triple the performance of the processor. The



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