Carbon nanotubes rewrite memory rulebook

New technology could soon overrun all the existing forms of memory used in computers, according to the company developing it.

Carbon nanotube memory could be a panacea to all existing memory issues, start-up Nantero said, because it was cheap and did not lose its contents if turned off. Currently computer memory comprises DRAM, S-RAM and NV-RAM (or flash memory).

DRAM, used in PCs and servers, is fast and cheap but its contents are lost when power is switched off. SRAM or Static RAM is faster and needs less power but is more expensive and also loses its contents when power is switched off. It is used most commonly for cache memory. NV-RAM is slower, power-hungry, very expensive but keeps its contents when power is switched off.

But Nanotube-based/Nonvolatile RAM (NRAM) could eventually replace all three. It is not without competitors though -- Phase-change memory and Magnetic RAM are also competing for the prize. So what's special about carbon nanotubes?

It's faster than SRAM, it should be cheap and it doesn't lose its contents when switched off. It should have an almost unlimited life, it should eventually be denser than DRAM, needs less power than DRAM and is resistant to radiation.

Nantero CEO, Greg Schmergel, claims carbon nanotube memory could be made with conventional CMOS manufacturing, keeping costs low. PCs using it could have an instant-on capability, no more lengthy boot time. Servers could have the speed of SRAM without the cost. Devices using flash could have greatly increased capacity for much lower cost. This would be nirvana for all of us and billionaire status for Nantero founders. How is it done?

A carbon nanotube is a microscopic pipe made of carbon, about 1/10,000th the diameter of a human hair -- that's one billionth of a meter thick. The pipe wall is just one atom thick.

The nanotube does actually have moving parts but these move on the atomic scale. The pipes are fabricated as ribbons, hang from a silicon wafer, and are suspended 100 nanometers above a carbon substrate layer. A charge applied to the ribbon causes a few atoms to move, making it bend and touch the substrate. This completes an electrical circuit, a permanent one, unless a different charge is applied. Then the moved atoms return to their original state breaking the circuit. Voila, binary ones and zeroes; ribbon-up gives us '?zero' and ribbon-down is 'one'.

There's just one problem: nobody knows if it can be manufactured beyond prototype units. A production chip would need millions of these ribbons manufactured cleanly and consistently and long enough to bend. Nantero, which has built a functioning prototype 10GB array, is working with development partners to achieve this.

LSI Logic is doing joint manufacturing development work with Nantero and hopes to build NRAM into its ASIC chips. It does not currently incorporate flash memory in these chips. Incorporating NRAM could make them much more powerful and customers wouldn't need to buy extra memory chips.

Schmergel said LSI Logic had a world-class fab and LSI Logic was an ideal partner in developing Nantero's carbon nanotube technology for high-volume manufacturing.

A manufacturing method could be in place in 2006. Eventually the silicon layer in the NRAM chips could replaced. A world-class but unnamed semi-conductor memory manufacturer has also just signed up to license and manufacture memory using Nantero technology. The full announcement should come later this month.

MRAM can also be made on conventional CMOS processes though, and Phase-change memory also uses a CMOS process plus a few steps. It looks like a rampant three-way tussle is coming.

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