AAWSAP DIRD, Metallic Spintronics, March 2010

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transistor switching can be reduced dramatically, the thermal load associated with 40
MW/cm 2 will exceed that in a rocket nozzle. The failure of thermal management on a
chip might end the continued progress of the semiconductor industry well before 2035.
The International Technology Roadmap for Semiconductors (http://www. itrs.net) has
termed this imminent collapse the "Red Brick Wall," where "Red" indicates no "known
manufacturable solutions" (of reasonable confidence) exist for continued scaling in
some aspect of the semiconductor technology.
The scenario above motivates the search for signal-processing devices that dissipate
very little energy when they switch . The emerging spintronic technology might offer
such devices where information is carried by spin-in contrast to CMOS transistors,
where it is carried by charge-since spin has an inherent advantage over charge when it
comes to energy dissipation. Therefore, if a reliable way can be found to control and
manipulate spins, spintronic devices could offer higher data processing speeds, lower
electricity consumption, and many other advantages over conventional chips, perhaps
including the ability to carry out radically new quantum computations .
A spintronic device calls for efficient methods to generate, conduct, process, and detect
spin-encoded signals . We have reviewed the physics and emerg ing applications of two
principal spintronic phenomena-giant magnetoresistance and spin-transfer-torque
that provide means to detect (GMR) and manipulate (STT) the spin signals. GMR has
already spawned major technological change in the information storage industry with
the usage of GMR sensors and read heads and, along with tunneling magnetoresistance
(TMR), is expected to continue to dominate the detection of spin-encoded signals. STT
is a more recent development in spintronics that provides an efficient means of
controlling and manipulating spin distributions on the nanometer length scale and the
picosecond-time scale, thus positioning STT as the method of choice for fast processing
of spin signals in nanodevices.
What is the future of spintronic applications? A number of new spintronic devices based
on GMR and STT have been proposed. These include high -frequency (GHz) oscillators,
sources, and detectors, as well as magnetic field sensors-for example, in nonvolatile
memories such as racetrack and STT magnetic random access memory (STT-MRAM) .
However, much fundamental work remains to be done before we see commercial
applications of these devices. For the memory industry, development of these spintronlc
applications may lead to a universal memory that would combine cost benefits of
DRAM, speed of SRAM, and nonvolatility of flash RAM. Potentially all logic operations on
a chip could be carried out by manipulating spins in metallic systems instead of
manipulating charges in semiconductor transistors, as in conventional microchips.
Moreover, such operations could be combined on a chip with a universal memory. This
would result in a new scalable and radiation-resistarnt electronics, computers, and so
forth . The radiation resistance would be of particular interest for aerospace applications
because the radiation in space is known to severely damage conventional electronics by
building up a destructive charge in transistors. Long space trips that would expose
onboard electronics to years of radiation would benefit from the radiation resistance
and reduced power consumption (for example, like a nonvolatile memory that can
retain the stored information even when not powered) of metallic spintronic devices.
More generally, the impact of reduced power consumption in electronic devices is hard
to overestimate, as we rely on such devices in almost every aspect of our everyday
lives.
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