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AMD tests ‘super silicon’ to beat heat problems

Pretty cool solution

When we cast doubt on AMD's abilty to produce an Athlon running at 1.7GHz that wouldn't run so hot it melted the solder on the mobo, we received the usual flood of 'you're in Intel's pocket' emails.

But in among the venom lurked an interesting item: a reader claimed that, for over 12 months, AMD has been quietly producing test chips using a new, pure version of silicon with greatly enhanced thermal properties, making a 1.7GHz Palomino a more practical proposition.

California-based Isonics produces an isotopically pure silicon which has much better thermal conductivity than natural silicon, meaning that heat can be removed more effectively. Isonics won't confirm it's working with AMD, stating only that "a major microprocessor manufacturer has modeled isotopically pure silicon wafers and has told us that the peak temperature of their advanced 1GHz microprocessor was reduced by 35 degrees celsius."

Heat sinks and on-board fans are not practical when CPU power goes above 100W. Intel's new Pentium 4 is rated at around 50W. Closed-loop cooling systems can increase the performance of existing designs, but they would cost more than the microprocessor itself.

Isonics believes it can profitably provide isotopically pure silicon bulk wafers for less than $10 per microprocessor, possibly much less. This compares with $10-30 for a fan and heat sink and looks a far better bet than a closed-loop cooling system costing several hundred dollars.

Isotopically pure silicon is chemically the same as regular silicon and can be used in existing manufacturing processes without any changes.

Warning: science ahead

Silicon exists in nature as three stable, non-radioactive, isotopes: Si-28 (92 per cent), Si-29 (five per cent) and Si-30 (three per cent). By purification at the sub-atomic level, it is possible to remove essentially all of the Si-29 and Si-30 leaving isotopically pure Si-28, which has a more perfect crystal structure.

This more perfect crystal structure exhibits reduced phonon-phonon and phonon-electron interactions which increases certain transport properties, such as thermal conductivity. It has been demonstrated in the laboratory that isotopically pure Si-28 has 60 per cent better room temperature thermal conductivity than natural silicon with its three isotopes.

Improvements in other physical and electrical properties are also theoretically possible. ®

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