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'Spin Transport' Controlled in Silicon

Photonics.com
May 2007
NEWARK, Del., May 21, 2007 -- The magnet-like spin properties of electrons have been measured and controlled in silicon for the first time, research that could lead to dramatically improved computers and cell phones.

The discovery advances the nascent field of spintronics, which focuses on harnessing electrons' spin properties instead of solely their charge to create exponentially faster, more powerful electronics such as quantum computers.
IanAppelbaum.jpg
Ian Appelbaum, assistant professor of electrical and computer engineering at the University of Delaware, and graduate student Biqin Huang (in the background) fabricated the first silicon spin-transport device, which could lead to the creation of more powerful electronics. (University of Delaware photos by Jon Cox)
The experiment, conducted in the laboratory of Ian Appelbaum, assistant professor of electrical and computer engineering at the University of Delaware, with doctoral student Biqin Huang, and in collaboration with Douwe Monsma, co-founder of Cambridge NanoTech in Cambridge, Mass., is reported in the May 17 issue of the journal Nature.

"Modern computers present serious challenges for conventional, silicon-based electronics. Ever-increasing demands on processor speed, memory storage and power consumption -- the era of the laptop that can keep us warm in winter is fast upon us -- are forcing researchers to explore unfamiliar territory in the quest for increased performance. In these endeavors, Appelbaum and colleagues report a possibly decisive development: the first demonstration of the transport and coherent manipulation of electron spin in silicon," said Igor Zutic of the Department of Physics at the State University of New York at Buffalo, and Jaroslav Fabian, of the Institute of Theoretical Physics at the University of Regensburg in Germany, about the research findings in Nature's "News and Views" section. 

While manipulating electron charge is the basis of the present-day electronics industry, over the past decade researchers have been exploring the capability of electron spin to carry, process and store information. A major goal in spintronics is to reach the precise level of control over electron spin that modern electronics has executed over electron charge.

"An electron has intrinsic angular momentum called spin," Appelbaum said. "The first step to making spintronic devices and circuits is to inject more spins of one direction than in the opposite direction into a semiconductor."
SiliconSpintronics.jpg
The world's first silicon spin-transport devices, fabricated and measured in Ian Appelbaum's lab at the University of Delaware. More than 25 individual silicon spin-transport devices are represented, one within each tiny wire grid, on this ceramic chip holder.
Silicon has been the workhorse material of the electronics industry, the transporter of electrical current in computer chips and transistors. Silicon also has been predicted to be a superior semiconductor for spintronics, yet demonstrating its ability to conduct the spin of electrons, referred to as "spin transport," has eluded scientists -- until now.

To provide conclusive evidence of spin transport in silicon, Appelbaum and Huang fabricated small, silicon semiconductor devices using a custom-built, ultrahigh vacuum chamber for silicon-wafer bonding. After spin injection, electrons in the silicon were then subjected to a magnetic field, which caused their spin direction to "precess" or gyrate (much like gravity's effect on a rotating gyroscope), producing tell-tale oscillations in their measurement.

"The processes of precession and dephasing, or decay, are the most unambiguous hallmarks for spin transport. Our work is the first time anyone has shown this effect in silicon," Appelbaum said. "It's an important problem to solve because silicon is the most important semiconductor for electronics. However, methods that worked for spin detection in other semiconductors failed in silicon.”"

Appelbaum said that pursuing the research was a risk worth taking. He credits Monsma with introducing him to hot-electron spin transport and applying it to the problem of spin detection in silicon several years ago when they were postdoctoral fellows together at Harvard University.

"We hope we're with spintronics where Bell Labs was with semiconductor electronics in 1948," Appelbaum said. That year, Bell announced the invention of the transistor, which laid the foundation for modern electronics.

Appelbaum's research was supported by grants from the US Office of Naval Research and by the Microsystems Technology Office of DARPA, the research and development arm of the US Department of Defense.
 
For more information, visit: www.udel.edu


GLOSSARY
electronics
That branch of science involved in the study and utilization of the motion, emissions and behaviors of currents of electrical energy flowing through gases, vacuums, semiconductors and conductors, not to be confused with electrics, which deals primarily with the conduction of large currents of electricity through metals.
gyroscope
See fiber optic gyroscope; ring-laser gyroscope; micro-optic gyroscope.
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
spin
Acronym for self-aligned polysilicon interconnect N-channel. A metal-gate process that uses aluminum for the metal-oxide semiconductor (MOS) gate electrode as well as for signal and power supply connectors.
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