Silicon Volley: Rivalry Makes the Chips Fly


Who will win the contest for making chips with the fastest clip? In late June, IBM rolled out a new transistor that it says will put communications chips in hyperdrive. Big Blue promised chips running at speeds of 100 gigahertz within two years, giving it a big jump over Intel. Just weeks earlier, the chipmaking giant said it had achieved a speed record for a transistor that would make it possible by 2007 to build chips capable of blazing along at 20 GHz.

Transistor speeds are determined by how quickly electricity races through them, which in turn depends on the material the transistor is made of and the distance electricity must travel through it. The two contenders are taking different approaches in their quests for faster computers and electronic devices. IBM is making its transistors from silicon modified by the addition of germanium ions, while Intel is working with conventional pure silicon and achieving faster speeds by making the circuits smaller.

IBM has been developing silicon-germanium (SiGe) for more than a decade. Chips from the modified silicon, once considered an "exotic" material, are already in some cell phones and fiber-optic network communications applications. The latest development relies on a new design to make electrons zip more rapidly through the transistors. The faster the transistors, the higher the speed of the chip that incorporates them.

VERTICAL DESIGN. In most transistors, electricity travels horizontally. To shorten the path, each transistor must be made smaller and smaller -- and some analysts have predicted that today's technology will soon reach its limits. But not any day soon, if IBM and Intel keep pushing the limit. IBM, for its part, turned to a vertical design, called a "heterojunction bipolar transistor." That made it easy to shorten the path that electrons must travel by making the layer of SiGe thinner.

The result is a transistor that switches on and off at a superfast 210GHz and draws just a thousandth of an amp of electrical current. IBM says this is an 80% improvement in performance and a 50% reduction in power consumption over present transistors. "Just as aircraft were once believed incapable of breaking the sound barrier, silicon-based transistors were once thought incapable of breaking a 200GHz speed barrier," says Bernard Meyerson, president of IBM's Communications Research and Development Center, who led the research effort.

Intel won its short-lived record by fabricating the smallest conventional transistors ever made -- a mere 20 nanometers, or 20 billionths of a meter across. At a mid-June conference for semiconductor engineers and scientists held in Kyoto, Japan, Intel revealed that the layer of conductive material needed to build the transistors was just three atoms thick.

The transistors are 30% smaller and 25% faster than the previous record holders developed by Intel researchers over the past year. A computer microprocessor constructed with them would operate on less than a single volt and contain a billion transistors that could turn on and off a trillion times a second. Intel calculates that such a microprocessor could churn through 4 million calculations in the time it takes a bullet to travel an inch. "We still have not found a fundamental limit for making silicon transistors smaller," says Robert Chau, Intel's director of transistor research.

STRAINED SILICON. Indeed, at the same conference, IBM revealed another development that it calls "strained silicon," a technique that could push the envelope for chips even further. Researchers discovered that depositing a layer of pure silicon on top of SiGe stretches the distance between the silicon atoms.

Strained silicon takes advantage of the natural tendency for atoms inside compounds to align with one another. The atoms in SiGe are spaced farther apart than those in pure silicon so the silicon atoms are pulled apart in the crystal lattice -- stretching, or "straining," the silicon. The result is that electrons flowing through the silicon layer experience less resistance and flow up to 70% faster.

In Kyoto, IBM predicted the new strained silicon technology would add another 35% to the speed of computer chips without further reductions in the size of transistors. It also said that it had successfully produced circuits with existing chipmaking systems, and it predicted that strained silicon would find its way into products in less than three years.

MORE MOORE. What are the implications? Both companies agree that the end isn't in sight for Moore's Law, an observation made by Intel co-founder and former Chairman Gordon Moore that computing power would double every 18 months. Intel figures that Moore's Law can keep chugging along for at least another decade. "We're able to extend Moore's Law scaling for at least another three generations beyond our current technologies," asserts Gerald Marcyk, director of the Components Research Lab in Intel's Technology and Manufacturing Group.

Says IBM's Myerson: "Silicon's future is safe as the preferred medium for chipmaking." So, naysayers aside, there still seems to be plenty of mileage left in silicon, the venerable element that sparked the information Age. By Alan Hall in New York


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