荷蘭愛因霍芬科技大學(Eindhoven University of Technology)的研究人員發現一種可讓磁阻隨機存取記憶體(MRAM)速度更快、密度更高且成本更低的全新製造方法，使其能以非揮發性替代方案達到取代RAM與快閃記憶體的「通用」記憶體目標。

MRAM Breakthrough Looms
Fast, dense and cheap finally achieved

Everybody in the memory business is trying to build a nonvolatile memory that is as fast as static random access memory (SRAM), as dense as flash and as cheap as read-only-memory (ROM). The problems with this "universal" memory (that could replace all others) has already been solved by magnetic random assess memories—according to those making MRAM.

Unfortunately, the optimization step to actually make nonvolatile MRAM faster, denser and cheaper—that MRAM makers keep promising—always seems to be three years away. Now independent researchers at Eindhoven University of Technology (TU/e, The Netherlands) claim to have solved the fast, dense and cheap problem with a novel new approach called "field-free magnetization reversal by spin-Hall effect and exchange bias"—or "current bending" for short.

Magnetic bits are quickly switched by bending electrons with the low-current pulses to attain the correct spin, while a special anti-ferromagnetic material makes the process cheap.
(Source: Arno van den Brink)

"The current density required to write magnetic bits becomes prohibitively high as bit dimensions are reduced," said the TU/e team of physicists led by professor Henk Swagten in their Naturepaper. "By interfacing the perpendicularly magnetized layer with an anti-ferromagnetic material, creating an in-plane exchange bias (EB) along the current flow direction, we demonstrate a spin-Hall effect driven magnetization reversal using only the intrinsic in-plane magnetic field caused by this EB." In other words, what they call "current bending" seems to solve the fast, dense and cheap problem of nonvolatile MRAM.

If you are familiar with MRAMs, then you already know that they store ones and zeros on the up or down spin of electrons, rather than accumulating or dissipating charge through a current-hogging tunnel barrier, thereby intrinsically saving energy to the max by what is called the "spin-Hall effect." Still they required spin-encoded electrons to be run through the ferromagnetic material to flip a bit, which did not scale well. In a nutshell, Swagten's team runs a tiny current pulse under a bit to flip its spin—hence the "current bending" moniker—which is not only more energy efficient, but scales like Moore's Law.

The experimental chip the researchers used for their characterization measurements of a fast, dense and cheap MRAM.
(Source: Arno van den Brink.)

The technique is also super-fast, according to the team, but still needed to be optimized for cost. The researchers claim to have solved that last problem by capping a layer of inexpensive anti-ferromagnetic material atop the bit cells, effectively "freezing" their magnetic field to meet the fast, dense and cheap goals.
Get all the details in Field-free magnetization reversal by spin-Hall effect and exchange bias

— R. Colin Johnson, Advanced Technology Editor, EE Times
編譯：Susan Hong

(參考原文：MRAM Breakthrough Looms，by R. Colin Johnson)

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