IBM scientists are moving closer to electronic memory that combines the best attributes of flash drives and the hard disk drives of computers. The breakthrough could lead to cheaper, more durable electronic devices that would hold far more data in the same amount of space and boot up more quickly.
Researchers say that within the next 10 years, racetrack memory – so named because the data “races” around the wire “track” – could mean that an mp3 player would hold some 500 000 songs or 3500 movies, 100 times today’s capacity. Racetrack storage would also use less power, generate less heat and be practically unbreakable. Unlike hard disk drives, racetrack memory has no moving parts. It also overcomes a major weakness of the flash drives: they can be used only a few thousand times because each “rewrite” causes slight damage.
“The promise of racetrack memory – f r example, the ability to carry massive amounts of information in your pocket – could unleash creativity leading to devices and applications that nobody has imagined yet,” said Dr. Stuart Parkin, the lead researcher on the project.
In the review paper that describes the fundamentals of racetrack, “Magnetic Domain-Wall Racetrack Memory,” Dr. Parkin and colleagues describe the use of magnetic domains to store information in columns of magnetic material (the “racetracks”) arranged perpendicularly or horizontally on the surface of a silicon wafer. Magnetic domain walls are then formed within the columns delineating regions magnetized in opposite directions (e.g. up or down) along a racetrack. Each domain has a “head” (positive or north pole) and a “tail” (negative or south pole). Successive domain walls along the racetrack alternate between "head to head" and "tail to tail" configurations. The spacing between consecutive domain walls (that is, the bit length) is controlled by pinning sites fabricated along the racetrack.
In their paper, the scientists describe their use of horizontal permalloy nanowires to demonstrate the successive creation, motion and detection of domain walls by using sequences of properly timed nanosecond long spin-polarized current pulses. The cycle time for the writing and shifting of the domain walls is a few tens of nanoseconds. These results illustrate the basic concept of a magnetic shift register relying on the phenomenon of spin momentum transfer to move series of closely spaced domain walls – an entirely new take on the decades-old concept of storing information in movable domain walls.
Ultimately, the researchers expect the racetrack to move into the third dimension (3D) with the construction of a novel 3D racetrack memory device, a paradigm shift from traditional two-dimensional arrays of transistors and magnetic bits found in silicon-based microelectronic devices and hard disk drives. By moving into the third dimension, racetrack memory stands to open new possibilities for developing less expensive, faster devices because it is not dependant on miniaturization as dictated by Moore’s Law.
Dr. Parkin’s advances with racetrack memory build on his prior accomplishments in memory technologies including the spin valve, and Magnetic Tunnel Junctions (MTJs) and breakthroughs in magnetic RAM (MRAM).
Racetrack memory encompasses the most recent advances in this realm, the field of metal spintronics. The spin-valve read head enabled a thousand-fold increase in the storage capacity of the hard disk drive in the past decade; the MTJ is in the process of supplanting the spin-valve because of its higher signal. MTJs also form the basis of modern MRAM, in which the magnetic moment of one electrode is used to store a data bit. Whereas MRAM uses a single MTJ element to store and read one bit, and hard disk drives use a single spin-valve or MTJ sensing element to read the approximately 100GB of data in a modern drive, racetrack memory uses one sensing device to read 10 to 100 bits.
Further understanding of the interaction of spin polarized current with magnetic moments is essential.
“For example, this might allow a reduction in the current density needed to manipulate or move domain walls. This would drop the power needed for racetrack further, and enable even lower power devices. We expect that our exploration of a wide variety of materials and structures will provide new insight into domain wall dynamics driven by current, making possible domain wall based memory and even logic devices that were previously inconceivable. It will not only change the way we look at storage, but the way we look at processing information. We’re moving into a world that is more data-centric than computing-centric,” said Dr. Parkin.