by Will Knight
A computer memory chip based on carbon nanotubes has passed a manufacturing milestone, according to the US company developing the technology.
The prototype chip would store information using hundreds of billions of nanotubes with a theoretical capacity of 10 gigabits of data, says Nantero, based in Boston, Massachusetts.
Once fully developed, the company says nanoscale random access memory (NRAM) could hold more data than existing types of RAM and would also be non-volatile, meaning data would not be lost when the power is been turned off. Computers using such memory could boot up almost instantly. Nantero also claims that NRAM would be much faster than current non-volatile memory, such as Flash.
Nantero is not the only company hoping to use carbon nanotubes to make improved types of computer memory. But the company believes its advantage lies in the fact that its chips can be made using existing silicon manufacturing methods and would therefore be relatively cheap to make.
Instead of trying to grow nanotubes in the correct alignment, Nantero applies them randomly across the entire surface of a silicon wafer. It then uses existing lithographic equipment to etch away the nanotubes that are not in the correct alignment.
"The creative breakthrough is to put nanotubes everywhere," Nantero's CEO Greg Schmergel told New Scientist.
The nanotubes remaining after etching are arranged in bunches across pairs of electrodes on the surface of the wafer. Applying a small electrical field alters the tubes so that they either bridge the gap between the electrodes or do not. These two states result in different conductivity that is easy to detect and can be used to represent a binary one or zero.
Nantero has now produced a wafer dotted with nanotube clumps, but is still developing the way of addressing each individual bunch. Schmergel says this is just a matter of harnessing existing silicon electronics technology.
Cees Dekker, an expert in carbon nanotubes at Delft University in the Netherlands, says the fabrication technique appears workable. But he says a potential problem lies in the difficulty of separating the different types of nanotubes that are created together during their creation.
"You have to find a way to deal with both semiconducting- and metallic-type nanotubes, which have rather different electrical properties," he told New Scientist.
Schmergel expects to have NRAM memory capable of storing up to four megabits in 18 months and components that could compete with current types of RAM in around three years.
NewScientist.com news service