Silicon Spin Chip Made

The first researchers to demonstrate that an electron's spin can be electrically injected, controlled and detected in silicon have now shown that these "hot" electrons can be transported through an entire silicon wafer, paving the way for the creation of silicon-based "spintronic" circuits.

Researchers at the University of Delaware (UD) and Cambridge NanoTech, a manufacturer of atomic layer deposition systems, were the first to demonstrate spin transport in silicon. Prior to their work, spin transport had only been measured in direct-bandgap semiconductors, or in combination with magnetic semiconductors.

Ian Appelbaum (right), University of Delaware assistant professor of electrical and computer engineering, and doctoral student Biqin Huang (holding a silicon spin chip) are making pioneering discoveries in spintronics, which seeks to harness an electron's spin in addition to its charge to make cheaper, faster, less power-hungry electronics. (Images: Kathy F. Atkinson/University of Delaware)

Their research in transporting electron spin through a 350-µm-thick undoped single-crystal silicon wafer, published in the Oct. 26 issue of the journal Physical Review Letters, mark another major steppingstone in the pioneering field of spintronics, which aims to use the intrinsic "spin" property of electrons versus solely their electrical charge for the cheaper, faster, lower-power processing and storage of data than present-day electronics can offer.

The research team included Ian Appelbaum, UD assistant professor of electrical and computer engineering; his doctoral student, Biqin Huang, who was lead author of the article; and Douwe Monsma of Cambridge NanoTech in Cambridge, Mass.

"Our new result is significant because it means that silicon can now be used to perform many spin manipulations both within the space of thousands of devices and within the time of thousands of logic operations, paving the way for silicon-based spintronics circuits," Appelbaum said.

This silicon spin chip made by UD researchers contains more than a dozen tiny spin-transport devices.

In Appelbaum's lab at UD, the team fabricated a device that injected high-energy, "hot" electrons from a ferromagnet into the silicon wafer. Another hot-electron structure (made by bonding two silicon wafers together with a thin-film ferromagnet) detected the electrons on the other side.
"Electron spin has a direction, like 'up' or 'down,' " Appelbaum said. "In silicon, there are normally equal numbers of spin-up and -down electrons. The goal of spintronics is to use currents with most of the electron spins oriented, or polarized, in the same direction."

In another paper published in the Aug. 13 issue of Applied Physics Letters, the team showed how to attain very high spin polarization, achieving more than 37 percent, and then demonstrated operation as the first semiconductor spin field-effect transistor.

"One hundred percent polarization means that all injected electrons are either spin-up or spin-down," Huang said. "High polarization will be necessary for practical applications. In the future, spintronics may bring a great change to daily life."

"We're taking the first steps at the beginning of a new road," Appelbaum said. "Before our initial work on spin transport in silicon, we didn't even know where the road was. There's a lot of fundamental work to be done, which we hope will bring us closer to a new age of electronics."

For more information, visit: www.udel.edu