IBM Research Spins 'Racetrack' Nano-Magnetic Memory

PORTLAND, Ore. — A next-generation nonvolatile memory dubbed "racetrack" is expected to initially replace flash memory and eventually hard-disk drives, according to IBM Corp. fellow Stuart Parkin of its Almaden Research Center (San Jose, Calif.)

Using spintronics--the storage of bits generated by the magnetic spin of electrons rather than their charge--a proof-of-concept shift register was recently demonstrated by IBM. The prototype encodes bits into the magnetic domain walls along the length of a silicon nanowire, or racetrack. IBM uses "massless motion" to move the magnetic domain walls along the nanowire for the storage and retrieval of information.

"We have now demonstrated a current-controlled, domain-wall, shift register which is the fundamental, underlying technology for racetrack memory," said Parkin. "We use current pulses to move a series of domain walls along a nanowire, which is not possible to do with magnetic fields."

IBM's goal, based on spintronic patents filed as early as 2004, is to use the same square micron that currently houses a single SRAM memory bit, or 10 flash bits, and drill down into the third dimension to store spin-polarized bits on a sunken racetrack-shaped magnetic nanowire. Using an area of silicon 1 micron wide and 10 microns high, IBM said its first-generation racetrack would store 10 bits compared to one, thereby replacing flash memory. Eventually, it could store 100 bits in the same area, which is dense enough to replace hard-disk drives.

"Racetrack is essentially the third turn of the crank of this new field of engineering called spintronics," said Parkin. "In current solid-state memory devices you store and control the flow of electrical charge. Here, we store and control the flow of the spin of an electron."

Parkin invented a spin valve sensing device in 1989 based on the giant magnetoresistive effect, which was used to increase disk drive capacity 1,000-fold. "Then we invented the use of the magnetic-tunnel junction (MTJ)--a sandwich of two magnetic layers separated by a dielectric--which we used to build the first magnetic random access memories in 1999.

"The third generation is the racetrack, which could replace all nonvolatile memories, including flash memory and hard-disk drives," Parkin claimed.

IBM estimates that an iPod using racetrack memory could store 100 times more information. Unlike flash, the solid-state devices have no components that can wear out.

Racetrack memory injects magnetized domain walls along the length of a high aspect ratio nanowire--only nanometers wide but up to microns long. Spin-polarized current pulses are then used to move the domain walls along the nanowire to store and retrieve bits.

Last year IBM, demonstrated that it could store a magnetic domain on a nanowire, then move it along the wire's length. The new shift register composed of many domain walls can be stored and moved together along the length of the wire. To read-out bits, the device senses a change in resistance in the wire.

The next step is building a fast MTJ read-head at the top of each racetrack, enabling it to quickly read-out any of the up to 100 bits stored on a racetrack.

IBM's current prototype uses a linear racetrack aligned parallel to the surface of a silicon chip. The first racetrack demonstration with MTJ read-heads will use that same approach. Eventually, IBM said it plans to build vertical racetracks by sinking nanowires into silicon. The MTJ read-head would be located at the top of each racetrack.