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Racetrack Memory

Stuart Parkin is using nanowires to create an ultradense memory chip.
February 24, 2009
ARTHUR MOUNT; SOURCE: IBM

When IBM sold its hard-drive business to Hitachi in April 2002, IBM fellow Stuart Parkin wondered what to do next. He had spent his career studying the fundamental physics of magnetic materials, making a series of discoveries that gave hard-disk drives thousands of times more storage capacity. So Parkin set out to develop an entirely new way to store information: a memory chip with the huge storage capacity of a magnetic hard drive, the durability of electronic flash memory, and speed superior to both. He dubbed the new technology “racetrack memory.”

Both magnetic disk drives and existing solid-state memory technologies are essentially two-dimensional, Parkin says, relying on a single layer of either magnetic bits or transistors. “Both of these technologies have evolved over the last 50 years, but they’ve done it by scaling the devices smaller and smaller or developing new means of accessing bits,” he says. Parki­n sees both technologies reaching their size limits in the coming decades. “Our idea is totally different from any memory that’s ever been made,” he says, “because it’s three-dimensional.”

The key is an array of U-shaped magnetic nanowires, arranged vertically like trees in a forest. The nanowires have regions with different magnetic polarities, and the boundaries between the regions represent 1s or 0s, depending on the polarities of the regions on either side. When a spin-polarized current (one in which the electrons’ quantum-mechanica­l “spin” is oriented in a specific direction) passes through the nanowire, the whole magnetic pattern is effectively pushed along, like cars speeding down a racetrack. At the base of the U, the magnetic boundaries encounter a pair of tiny devices that read and write the data.

This simple design has the potential to combine the best qualities of other ­memory technologies while avoiding their drawbacks. Because racetrack memory stores data in vertical nanowires, it can theoretically pack 100 times as much data into the same area as a flash-chip transistor, and at the same cost. There are no mechanical parts, so it could prove more reliable than a hard drive. Racetrack memory is fast, like the dynamic random-access memory (DRAM) used to hold frequently accessed data in computers, yet it can store information even when the power is off. This is because no atoms are moved in the process of reading and writing data, eliminating wear on the wire.

Just as flash memory ushered in ultra­small devices that can hold thousands of songs, pictures, and other types of data, racetrack promises to lead to whole new categories of electronics. “An even denser, smaller memory could make computers more compact and more energy efficient,” Parkin says. Moreover, chips with huge data capacity could be shrunk to the size of a speck of dust and sprinkled about the environment in tiny sensors or implanted in patients to log vital signs.

When Parkin first proposed racetrack memory, in 2003, “people thought it was a great idea that would never work,” he says. Before last April, no one had been able to shift the magnetic domains along the wire without disturbing their orientations. However, in a paper published that month in Science, Parkin’s team showed that a spin-polarized current would preserve the original magnetic pattern.

The Science paper proved that the concept of racetrack memory is sound, although at the time, the researchers had moved only three bits of data down a nanowire. Last December, Parkin’s team successfully moved six bits along the wire. He hopes to reach 10 bits soon, which he says would make racetrack memory competitive with flash storage. If his team can manage 100 bits, racetrack could replace hard drives.

Parkin has already found that the trick to increasing the number of bits a wire can handle is to precisely control its diameter: the narrower and more uniform the wire, the more bits it can hold. Another challenge will be to find the best material for the job: it needs to be one that can survive the manufacturing process and one that allows the magnetic domains to move quickly along the wire, with the least amount of electrical current possible.

If the design proves successful, racetrack memory could replace all other forms of memory, and Parkin will bolster his status as a ­magnetic-memory genius. After all, his work on giant magnetoresistance, which led to today’s high-capacity hard drives, transformed the computing industry. With racetrack memory, ­Parkin could revamp computing once more.

ARTHUR MOUNT; SOURCE: IBM

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