Spin-transfer torque (STT) is an effect in which the orientation of a magnetic layer in a

magnetic tunnel junction Tunnel magnetoresistance (TMR) is a magnetoresistive effect that occurs in a magnetic tunnel junction (MTJ), which is a component consisting of two ferromagnets separated by a thin insulator. If the insulating layer is thin enough (typically a fe ...

spin valve A spin valve is a device, consisting of two or more conducting magnetic materials, whose electrical resistance can change between two values depending on the relative alignment of the magnetization in the layers. The resistance change is a result ...

can be modified using a spin-polarized current. Charge carriers (such as electrons) have a property known as

spin Spin or spinning most often refers to: * Spinning (textiles), the creation of yarn or thread by twisting fibers together, traditionally by hand spinning * Spin, the rotation of an object around a central axis * Spin (propaganda), an intentionally b ...

which is a small quantity of

angular momentum In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational analog of linear momentum. It is an important physical quantity because it is a conserved quantity—the total angular momentum of a closed syst ...

intrinsic to the carrier. An electric current is generally unpolarized (consisting of 50% spin-up and 50% spin-down electrons); a spin polarized current is one with more electrons of either spin. By passing a current through a thick magnetic layer (usually called the “fixed layer”), one can produce a spin-polarized current. If this spin-polarized current is directed into a second, thinner magnetic layer (the “free layer”), the angular momentum can be transferred to this layer, changing its orientation. This can be used to excite

oscillations Oscillation is the repetitive or periodic variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples of oscillation include a swinging pendulum ...

or even flip the orientation of the magnet. The effects are usually seen only in nanometer scale devices.

Spin-transfer torque memory

Spin-transfer torque can be used to flip the active elements in magnetic random-access memory. Spin-transfer torque magnetic random-access memory (STT-RAM or STT-MRAM) is a

non-volatile memory Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data. Non-volatile memory typic ...

with near-zero leakage power consumption which is a major advantage over charge-based memories such as SRAM and

DRAM Dynamic random-access memory (dynamic RAM or DRAM) is a type of random-access semiconductor memory that stores each bit of data in a memory cell, usually consisting of a tiny capacitor and a transistor, both typically based on metal-oxid ...

. STT-RAM also has the advantages of lower power consumption and better scalability than conventional

magnetoresistive random-access memory Magnetoresistive random-access memory (MRAM) is a type of non-volatile random-access memory which stores data in magnetic domains. Developed in the mid-1980s, proponents have argued that magnetoresistive RAM will eventually surpass competing tec ...

(MRAM) which uses magnetic fields to flip the active elements. Spin-transfer torque technology has the potential to make possible MRAM devices combining low current requirements and reduced cost; however, the amount of current needed to reorient the magnetization is presently too high for most commercial applications, and the reduction of this current density alone is the basis for present academic research in spin electronics.

Industrial development

Hynix Semiconductor and Grandis formed a partnership in April 2008 to explore commercial development of STT-RAM technology. Hitachi and Tohoku University demonstrated a 32-Mbit STT-RAM in June 2009. On August 1, 2011, Grandis announced that it had been purchased by Samsung Electronics for an undisclosed sum. In 2011,

Qualcomm Qualcomm () is an American multinational corporation headquartered in San Diego, California, and incorporated in Delaware. It creates semiconductors, software, and services related to wireless technology. It owns patents critical to the 5G, 4 ...

presented a 1 Mbit Embedded STT-MRAM, manufactured in

TSMC Taiwan Semiconductor Manufacturing Company Limited (TSMC; also called Taiwan Semiconductor) is a Taiwanese multinational corporation, multinational semiconductor contract manufacturing and design company. It is the world's most valuable semicon ...

's 45 nm LP technology at the

Symposium on VLSI Circuits The Institute of Electrical and Electronics Engineers (IEEE) is a 501(c)(3) professional association for electronic engineering and electrical engineering (and associated disciplines) with its corporate office in New York City and its operation ...

. In May 2011, Russian Nanotechnology Corp. announced an investment of $300 million in Crocus Nano Electronics (a joint venture with

Crocus Technology Crocus Technology, founded in 2006, is a venture-capital-backed semiconductor startup company developing magnetoresistive random-access memory (MRAM) technology. The company's products originated in a Grenoble-based Spintec laboratory and its te ...

) which will build an MRAM factory in Moscow, Russia. In 2012

Everspin Technologies Everspin Technologies is a public semiconductor company headquartered in Chandler, Arizona, United States. It develops and manufactures discrete magnetoresistive RAM or magnetoresistive random-access memory (MRAM) products, including Toggle MRA ...

released the first commercially available

DDR3 Double Data Rate 3 Synchronous Dynamic Random-Access Memory (DDR3 SDRAM) is a type of synchronous dynamic random-access memory (SDRAM) with a high bandwidth ("double data rate") interface, and has been in use since 2007. It is the higher-speed ...

dual in-line memory module A DIMM () (Dual In-line Memory Module), commonly called a RAM stick, comprises a series of dynamic random-access memory integrated circuits. These memory modules are mounted on a printed circuit board and designed for use in personal computers, ...

ST-MRAM which has a capacity of 64 Mb. In June 2019

started pilot production for 28 nm 1 Gb STT-MRAM chips. In December 2019

Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 seri ...

demonstrated STT-MRAM for L4-cache Other companies working on STT-RAM include Avalanche Technology,

and Spin Transfer Technologies.

References

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External links

Spin torque applet
* J.C. Slonczewski:"Current-driven excitation of magnetic multilayers(1996)", Journal of magnetism and magnetic materials volume 159, issues 1-2, June 1996, pages L1-L

Spintronics

Spin-transfer torque memory

Industrial development

See also

References

External links