A new type of nonvolatile memory based on carbon nanotubes has dramatically lower power requirements than current technology. It uses the nanotubes to read and write data to small islands of phase-change materials, which store information. With further development, the new technology could extend battery life in mobile devices and also make desktop computers more efficient.
Nonvolatile memory stores information even when the power is switched off. The standard technology for it, flash memory, is used in smart phones, cameras, USB sticks, and fast-booting netbook computers. But the storage density of flash memory is reaching its limit because the transistors used to make flash memory arrays cannot be miniaturized any further. The power needed to write to flash is also a speed limitation, and it drains the batteries in portable devices.
The new nonvolatile memory, developed by Eric Pop, professor of electrical engineering and computer sciences at the University of Illinois at Urbana-Champaign, and colleagues, can hold more data than flash while requiring considerably less power.
A few replacements for flash are in development. The one that’s closest to commercialization is phase-change memory. The “bits” in phase-change memory are small islands of materials called chalcogenides that switch between glassy and crystalline states when rapidly heated. The two phases have different electrical resistances that can represent “1” or “0”—the bits are read by passing a small current through an electrode to read the resistance. Samsung and Numonyx, a memory company owned by Micron, have both promised to release phase-change memory products soon.
While phase-change memory promises to be denser than flash, for the most part it still has relatively high power requirements. “The traditional drawback of phase-change memory is that you need significant heat to change the phase,” says Victor Zhirnov, director of special projects at the Semiconductor Research Corporation.
The device designed by Pop and colleagues at the University of Illinois tackles the power consumption problem by allowing the phase-change memory bits to be further miniaturized. The smaller the chalcogenide bit, the less the energy required to heat it up and change its phase.