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Improvements to spin-torque transfer (STT) MRAM bring technology closer to market readiness

MRAM, or MeRAM, is the acronym bandied about for magnetoresistive random access memory, one of several novel competitors vying to insert itself as the replacement to current digital storage technologies.

I. MRAM -- NAND Killer?

Electrical engineering Professor Kang L. Wang at UCLA -- the University of California, Los Angeles -- have come up with a refinement to a special type of MRAM, which they feel is a key improvement that moves the technology closer to broader commercial availability (some MRAM products are being currently sold, but at low volume due to the cost).

The UCLA team says the new storage nanocells represent a 10 to 1,000 times power efficiency bump over traditional MRAM designs during the power-intensive write cycle.

Unlike traditional flash memory, which operates using cells that stored values via charge, MRAM cells consist of little nanoscopic "sandwiches", stacks of specially prepared materials.  Typically these materials contain a pair of tiny magnetic plates, one permanent, and one adjustable.  To write to MRAM, a current induces a shift in polarity, which will remain fixed until the next write.

MRAM is expected to enjoy longevity and speed advantages over NAND or traditional hard-drive-based magnetic storage (which is inherently very slow due to the need for moving parts).

Spintronics
The new MRAM is part of a collection of emerging circuit technologies called "spintronics".  Spintronics involves tweaking electron spins to generate novel behavior.
[Image Source: Big Bang Gadget]

MRAM was first developed in the 1990s.  A major improvement arrived more recently with the development of spin-transfer torque (STT), a special MRAM technique that uses polarized electrons to trigger a cascade effect and "write" the magnetic value to a nanoscopic in-cell plate.

STT is attractive because unlike with older MRAM designs, it does not require significantly more power to perform a write cycle.  However, it still suffered from heat and leakage issues due to the fact that it still required a fair amount of current.

II. Tweaking Spin-Torque

To tackle that challenge, Professor Wang's team modified MRAM cells to use voltage -- a potential difference -- rather than direct current to perform an STT-style write.  

Pedram Khalili, a project manager at UCLA-DARPA who participated in the research explains, "The ability to switch nanoscale magnets using voltages is an exciting and fast-growing area of research in magnetism.  This work presents new insights into questions such as how to control the switching direction using voltage pulses, how to ensure that devices will work without needing external magnetic fields, and how to integrate them into high-density memory arrays."

"Once developed into a product.  MeRAM's advantage over competing technologies will not be limited to its lower power dissipation, but equally importantly, it may allow for extremely dense MRAM. This can open up new application areas where low cost and high capacity are the main constraints."

MRAM
By using voltage instead of current, UCLA researchers have greatly improved write power performance for MRAM spintronic cells. [Image Source: UCLA]

STT MRAM is often referred to under the umbrella term "spintronics", which refers to circuit elements that rely on controlling the spin of electrons to accomplish goals.

Industry observers are clearly pretty interested in the more refined recent iterations of MRAM.  Among the participants in the project was Hitachi Global Storage Technologies, a subsidiary of hard-drive giant Western Digital Corp. (WDC).  The military is also intrigued; the project received funding from the U.S. Defense Advanced Research Projects Agency (DARPA) NV Logic Program.

A paper on the work was published at Dec. 12 at IEEE's 2012 International Electron Devices Meeting (IEDM) in San Francisco, a top electrical engineering conference held annually in Silicon Valley.

Source: UCLA



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This article is over a month old, voting and posting comments is disabled

By trisct on 12/20/2012 2:02:06 PM , Rating: 2
Memristors are a competing technology to this one, which is likely to offer similar benefits.

Memristors are an HP property though, so others will try to find alternatives. It will all boil down to price, density, power and longevity. I think memristors are further along, so we'll probably see them first. This technology looks like it could be denser (more bits per chip) though.


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