Carbon nanotubes in a race against time to replace silicon

Nascent carbon nanotube chip technology may save the computer industry from silicon’s presumed looming demise. Or it may not.

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Alternatives are finite and few

For all its problems, the compass continues pointing toward CNT technology as a possible way to keep up with Moore's Law -- assuming no way is found to make ever-smaller silicon components.

"To make transistors you need a material with three things," says Shulaker at Stanford. The material needs a band gap -- an energy range within which electricity can't be conducted -- so that the circuit can be turned on and off. The band gap needs to be just the right size; too large and the material is an insulator, too small and it's a metal.

"CNTs have one just the right size," Shulaker says. Finally, the material needs to be thin since you want to make the circuits small. And it needs to be a very good conductor.

"There are not many materials with all three properties," he notes.

Another factor is that "any new technology needs to be mindful that silicon has dominated the industry for decades, and billions have been invested in the infrastructure. But CNTs are 100% compatible with silicon, as you can build them on a silicon substrate," Shulaker says.

Shulaker adds that CNTs can actually be superior to silicon in that a layer of CNT circuitry can be added to an existing silicon device, since the process requires applying heat at 120 degrees centigrade. Adding a layer of silicon would require 900 degrees centigrade, which would destroy the original layer.

"Huge amounts of energy are wasted in computers moving data from memory to the processor, but monolithic integrated 3D [chips], with transistors and memory stacked directly on top of each other, would give huge performance benefits," he says.

"You could build a whole computer on a dime. Beyond better transistors you would get brand-new types of systems; it could lead to a whole new world," Shulaker says.

"I am hopeful that CNTs will be used someday," he adds. "It does not need to replace silicon, it can be built atop silicon, and therefore it doesn't need to do everything at once."

Gwennap likens the generation-by-generation development of chip technology to driving down a dark road at night, where only what is in the range of the car's headlights can be seen.

"I can see 10nm, I can see 7 pretty well, and I hear 5nm is pretty solid, but nobody knows what happens after that," Gwennap notes. "Below 5nm it seems like it has to stop somewhere, but I am skeptical of saying that since I have heard others say it, and I have said it myself over the past 20 years, that we can't get below a certain size. But CNTs can only be 1nm, and if silicon gets below that it obviates the need for CNTs," says Gwennap.

"But we have been in this situation for decades, where we can't see more than five years out," he adds. "Somehow, here we are."

Copyright © 2015 IDG Communications, Inc.

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