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Last Updated: Wednesday, 25 August, 2004, 17:28 GMT 18:28 UK
Door open for silicon replacement
Chip, Eyewire
Current silicon chips are vulnerable to heat
A replacement for the use of pure silicon in electronics has come a step closer, the journal Nature reports.

Silicon chips can malfunction at high temperatures, often from the heat generated in their own circuitry.

But Japanese experts have now overcome the flaws that plague crystals of silicon carbide, a hard compound that is more robust in hot conditions.

This material could now fulfil its potential as a replacement for pure silicon in manufacturing processes.

Silicon carbide has become, at last, a contender for silicon's crown
Roland Madar, CNRS
Silicon carbide (SiC) could be used to make electronic devices that can operate at high power, in fierce heat or at lethal doses of radiation.

If the breakthrough can be carried forward commercially, it could spawn a wide range of improved devices, including electronics that work in red-hot jet engines, better wireless communications and radar, as well as improving smart devices that optimise performance in cars.

Wafer slice

Scientists from Toyota Central R&D Labs and Denso Corporation have developed a new way of making silicon carbide crystals that lead to the production of larger and more reliable wafers of this material.

This would render them cheaper and more useful commercially.

Conventional computer chips are made from a thin slice of silicon. This is manufactured by cooling pure, molten silicon so that as it solidifies a crystal of the material forms in a certain direction.

Silicon wafers are then chemically "doped" with impurities to improve their ability to carry an electrical charge.

The types of impurities added affect the direction of the charge. However, the weakness of devices based on silicon is their sensitivity to heat.

Silicon wafer, Intel
Chips are currently made from silicon wafers
This factor requires fans or other gadgets to cool them down and limits their future miniaturisation.

The potential of silicon carbide as a replacement for silicon has been known since the 1950s. It is extremely hard, being used as grit in sandpaper, and highly resistant to heat.

In the 1970s, scientists developed a new technique called physical vapour transport for producing large silicon wafers. But the wafers produced this way were of poor quality.

They were prone to flaws called micropipes. These are hexagonal tube-like cavities that damage or weaken the circuitry and would make any chip made from the material vulnerable to failure.

Great pretender

The new way of growing silicon carbide crystals has overcome this problem.

Kazumasa Takatori of Toyota and his colleagues found a solution by growing the crystals in several different stages.

At each stage, the crystal is carefully rotated so that the solidifying compound crystallises on the best, least-blemished face.

The scientists patiently built up the crystal layer-by-layer. This allowed them to create ingots of silicon carbide - the little bricks from which wafers are sliced - that were "virtually dislocation-free", they claim.

The researchers call their method Repeated A-Face (RAF) growth.

"These results are spectacular," said materials scientist Roland Madar, of the Centre National de la Recherche Scientifique, (CNRS) in Grenoble, France.

"The [layering] process is a major innovation in materials science. Silicon carbide has become, at last, a contender for silicon's crown."

Previous research has already shown that even at red-hot temperatures as high as 650C (1,202F), silicon carbide devices can function unperturbed and without the need for cooling.

One exciting application for silicon carbide could be in deep-space missions, where nuclear power would be needed for the craft. Radiation-hardened silicon carbide devices would reduce the shielding needed to protect reactor control electronics.

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