The future of chip technology

By Andy Walker

It was an inevitable declaration, a revision that fundamental physics was going to extort from Gordon Moore sooner or later. Silicon-based computers can't continue to double in speed every two years forever. Moore, who laid out that remarkably accurate roadmap 35 years ago, concedes to that point.

"Chip doubling will go from every couple of years to five years," he said without hesitation.

The revision to Moore's Law, which he has been quietly making lately, is made from an Intel office in Santa Clara, a short highway drive from the Palo Alto office where, in 1965, he made the initial observation.

At the time, Moore worked at Fairchild Semiconductor, one of Silicon Valley's first start-up companies. This was three years before he confounded Intel with the late Bob Noyce.

"I extrapolated the idea that we would go from 60 components on a chip to 60,000 over 10 years," Moore recalled. The initial law, named by Carver Mead, a professor at California Institute of Technology, predicted a doubling every year, but 10 years later Moore revised the timeline to every two years.

The revision is necessary. Experts in the semiconductor industry believe there are only about 10 to 15 years left before chipmakers run out of ways to pack more transistors on chip, the technique to make chips faster.

"You can imagine there will be a great difficulty if you try to print a line (on a silicon wafer) that is smaller than the space between the atoms in silicon. Physics gets in the way after a while," said Howard High, who for 21 years has watched Moore's Law in action from inside Intel as the company's strategic communications manager.

The 42 million transistors on the new Pentium 4 chip are each 0.18 microns wide or 180 nanometers. A human hair is 100 microns wide.

By 2011, it will be possible to shrink line widths to 0.025 microns or 25 nanometers, estimates the International Technology Roadmap for Semiconductors, published in 1999.

More transistors mean faster chips. By then, a billion transistors on a chip should be possible. That should produce chips that will run well over 10 GHz. "Maybe you're going to get 12, 15, 20 gigahertz," said High.

It could go even smaller. "We have proof of concept in the 20 nanometer range," said Ralph Cavin, senior vice-president of research at the Semiconductor Research Corporation in Research Triangle Park, N.C.

Experts know the numbers they use are speculative. High pointed to a 1989 research paper project that looked ahead at what microprocessors might look like today. "At that time, they worked at 25 to 40 MHz," he said. "The prediction was they would reach 250 MHz by 2000, but here we are, at the threshold of 2 GHz," eight times faster than the vision of 11 years ago.

If scientists lose miniaturization as tool to boost chip speeds, Moore believes new ways to speed up silicon chips will be found.

"We will have to push technology as far as we can by shrinking, then we will start making bigger chips," he said.

In a quest for more transistors, chipmakers could also start sandwiching chips together, place two chips together face-to-face or put multiple chips together.

They could also try to move data around the chip faster. Intel has been experimenting with ways of pulsing data across chips using super-circuits made of industrial diamonds.

Even if scientific barriers can be overcome, another force may halt progress: economics.

"Every time someone does a study on when we will hit those (scientific) limits, we don't ever hit them. You hit other, more important, financial barriers," said Russ Lange, chief technologist at IBM Microelectronics.

As chips get smaller, the cost to build them rises. A new, more expensive factory has to be built each time chip architecture changes.

There's a lot of to be done if Moore's Law is going to stay on course over the next five years. Line widths need to shrink to 100 nanometers by 2005.

Chip engineers still face some difficult problems in getting there. As transistors get smaller, they need a high concentration of chemical impurities added to the wafer to help hold an electrical charge called dopants but, at high concentrations, dopants clump together and become electrically inactive. Engineers still have to solve this challenge.

Fluctuations in dopant concentration are also a factor. Chips with larger transistors are unaffected, but as transistors get smaller, they become more susceptible and could behave unpredictably.

And then, there are "gates", the tiny barriers - one or two nanometers - controlling the flow of electrons in a transistor. A gate denotes whether a chip counts one or zero. An open gate lets an electron through as zero. A closed gate blocks it to count as one. This is the basis for binary math, the engine for all computer calculations.

Electrons go rogue occasionally. They bolt through a gate and appear on the other side. It's a quantum physics oddity called "tunneling", causing errors in calculation. With no known solutions, chip experts still believe they can solve these problems.

"There was time when people swore we couldn't get lower than one micron. That was around 1979," said High.

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