Intel mulls metal over silicon for new chips

Moore's Law is alive and well, but Intel is changing its basic semiconductor recipes to make sure that it stays that way.

The Santa Clara, Calif.-based chipmaker is looking at revamping two fundamental elements of its transistors--the transistor gate and the gate dielectric--so that its chips will continue to increase in speed and performance.

Currently, the gate, which controls whether a transistor is on or off, is made of silicon atoms, while the gate dielectric, an insulating layer below the gate, is made of silicon dioxide. By making both out of metal, Intel will be able to clamp down on electricity leakage and other looming problems that could put a lid on improvement. In experiments, the new transistors are setting records on certain parameters, according to the company.

"We'd love to continue with silicon dioxide, but we can't do it because of leakage," said Ken David, director of components research in Intel's Technology and Manufacturing Group. "People keep running into these fundamental roadblocks."

Chips that have metallic gates and metallic gate dielectrics (also called high-k dielectrics) may appear in 2007 with the 45-nanometer manufacturing process.

Semiconductor design is currently undergoing a major overhaul and prompting engineers and designers to incorporate new structures or materials into chips at a more rapid rate than ever before. "The way the industry has approached it is (to) change one material at a time," David said. Now, semiconductor designers are being asked to incorporate two or more novel concepts every two years.

Some of these technologies are already coming to the fore. Intel recently started to make processors with strained silicon, a design convention that lets electrons move more rapidly, while IBM has already released a dual-core processor.

Other ideas on the drawing board include using multiple-gate transistors, controlling transistor voltage, replacing wires inside chips with optical fiber and using carbon nanotubes.

The catch, of course, is that it isn't easy. When Advanced Micro Devices tried to incorporate silicon-on-insulator technology into its Athlon chips, it suffered a number of delays and eventually had to hire IBM to help. Unforeseen problems for all manufacturers are inevitable.

The changes are largely necessary because of the unsavory consequences of Moore's Law, the famous dictum that the number of transistors on a chip doubles every two years.

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Transistor count can be doubled, because engineers can shrink the size of their transistors. Shrinkage, though, has made heat a major problem, because millions of circuits are now crammed into small spaces where only a few hundred thousand transistors may have existed years before.

With the gate dielectric, thinness is an issue. The gate dielectric on chips that are coming out of Intel's fabs next year will only be four to five atoms thick, David said. Thinning it further will cause additional leakage, or unintentional energy dissipation. Leakage can drain batteries and increase internal computer heat because more energy than should be necessary is required to animate these chips.

By switching to metal, leakage decreases because the chemical and physical properties of metal prevent electricity from escaping. With less leakage, chips can provide comparable performance on far less electricity or can run at a higher speed at the same energy levels.

As an added bonus, the gate dielectric layer can actually be thicker, which makes it easier to manufacture, but it will perform like a very thin traditional gate dielectric.

AMD has reported similar results in its published experiments.

Switching to metal gates and high-k gate dielectrics also eliminates phonon scattering. Increasingly, the atoms inside transistors are vibrating. Incorporating high-k gate dielectrics alone does not solve the problem.

"This slows down the mobility of electrons," David said. "The metal gate seems to act like a sink for this phenomenon."

David, however, declined to identify what metals Intel is experimenting with. AMD is working with nickel in its metal gates.

Intel is presenting the results of its research into metal gates at the International Workshop on Gate Insulator this week in Tokyo.