Buckminsterfullerene Strikes Again - Nanotube RAM

putaro writes "Nanotube based RAM, under development by Nantero, promises to deliver densities of over 1 terabit per cm^2, is non-volatile and faster than current DRAM. The Economist has a nice story. Forget about just kicking DRAM's and FLASH's butt, is this finally the end of magnetic storage as well?"

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Details

[robbyjo]

Here's a little details that pretty much summarize the docs:

How it works. Nantero's memory chips consist of billions of nanotubes, each a few hundred nanometres long, suspended from a silicon wafer. ... This means that a group of a few dozen nanotubes can act as a memory element, storing a single bit (either a one or a zero) of the binary code that computers use to operate. If the connection between the wafers is live at a particular point, the bit represented is a one. If not, it is a zero.

Speed. Nantero's new memory can read or write a bit in as little as half a nanosecond.

Availability. At the moment, Nantero has only a working prototype. But the firm aims to have memories on the market within a year.

Hurdles. The main difficulty faced by others who have tried to go down the buckytube route is getting the tubes to align with each other when they are hung from the first wafer. Until now, the approach has been to try to grow all of the tubes in the correct orientation to start with. But Nantero's founders came up with a simpler, if less elegant, solution. They use established lithographic techniques to get rid of tubes that are pointing in the wrong direction by zapping them with an electron beam. That leaves only those that are hanging down towards the opposite wafer.

The Science Behind the Technology

[citanon]

For those who are interested, the Nantero's technology is based on earlier work in the lab of Charles M. Lieber. The original paper was published in the journal Science. Rueckes et al, Science, Vol 289, P. 94. Rueckes went on to found Nantero.

The original experiment worked as follows:

One rope of singled walled carbon nanotubes sits suspended above another in a crossbar configuration. When an electric charge is applied, the top nanotube rope bends downward, where it is held in place by van der waals attraction to the bottom rope. To deactivate the switch, another charge is applied to repel the bent nano-rope into its original position.

This electromechanical switch works as a switch because of tunneling of electrons between the upper rope and the lower rope. When the ropes are sticking together, enough electrons tunnel from the upper to the lower, or vice versa so that one can measure a good signal, turning the switch on. When the ropes are apart, the tunneling conductance drops by several orders of magnitude, turning the switch off.

The original experiment was done with bundles of carbon nanotubes. In principle, the concept should work at much higher densities for single nanotubes, but the technology still has hurdles to cross. Currently, the tubes conduct because ropes of tubes are likely to contain both semiconductor type and metal type tubes. Since metal type tubes are fantastic conductors, having even a few of them in a rope will allow a device to work. However, when one crosses the threshold to single nanotubes, the device will only work if the tubes are metal type. Hence, an important problem will be finding a way to produce only metal type single walled nanotubes. Currently, carbon nanotubes are produced in a mixture of semiconductor type and metal type nanotubes. It's difficult to control that property because it depends sensitively on the way the sp2 bonds on the nanotube sidewall line up, something that no one yet knows how to control.