ICs could run on heat waste, rather than electricity, researchers believe

Researchers at Ohio State University are trying to combine spintronics, the utilization of the spin of electrons to read and write data, with thermo-electronics, devices that convert heat to electricity. The hybrid technology, "thermo-spintronics," would convert heat to electron spin.

By Suzanne Deffree, Managing editor, news -- EDN, September 29, 2010

Researchers at Ohio State University believe that the material gallium manganese arsenide may allow computers to one day recycle part of the heat they produce into power.

In their study of the material the researchers detected an effect that converts heat into spin in a semiconductor. Once developed, the effect could enable ICs that run on heat, rather than electricity, the university said.

The research was lead by Joseph Heremans, Ohio eminent scholar in nanotechnology, and Roberto Myers, assistant professor of materials science and electrical engineering at Ohio State University. It focused on thermo-electricity and spintronics.

Myers and Heremans are trying to combine spintronics, the utilization of the spin of electrons to read and write data, with thermo-electronics, devices that convert heat to electricity. The hybrid technology, "thermo-spintronics," would convert heat to electron spin.

If successful, thermo-spintronics would help remove waste heat from computers and boost computing power without creating more heat.

"Spintronics is considered as a possible basis for new computers in part because the technology is claimed to produce no heat," Heremans said in a statement. "Our measurements shed light on the thermodynamics of spintronics, and may help address the validity of this claim."

Myers further noted that a main limiting factor to smaller, denser ICs is the heat those IC produce.

"All of the computers we have now could actually run much faster than they do, but they're not allowed to - because if they did, they would fail after a short time," Myers said in the statement. "So a huge amount of money in the semiconductor industry is put toward thermal management."

The university suggested one future possible use of thermo-spintronics would be a device that could sit atop a traditional microprocessor and siphon waste heat away to run additional memory or computation.

Research details

The Ohio State researchers studied how heat can be converted to spin polarization, an effect called the spin-Seebeck effect that was first identified in a 2008 paper and detected in a piece of metal, rather than a semiconductor.

The Ohio State measurements focused on the effect in gallium manganese arsenide, a semiconductor material used in cell phones today. In the university's work, the addition of the element manganese endows the material with magnetic properties.

Samples of this material were prepared into thin single-crystal films. The researchers said that in this type of material the spins of the charges line up parallel with the orientation of the sample's overall magnetic field. The researchers noted that as such, when they were trying to detect the spins of the electrons, they were really measuring whether the electrons in any particular area of the material were oriented as "spin-up" or "spin-down."

In the experiment, the researchers heated one side of the sample, and then measured the orientations of spins on the hot side and the cool side. They reported that on the hot side, the electrons were oriented in the spin-up direction, and on the cool side, they were spin-down.

The researchers also discovered that two pieces of the material do not need to be physically connected for the effect to propagate from one to the other.

"We figured that each piece would have its own distribution of spin-up and spin-down electrons," said Myers. "Instead, one side of the first piece was spin up, and the far side of the second piece was spin down. The effect somehow crossed the gap." 

The research is detailed in the current online edition of Nature Materials.

The work was supported by the National Science Foundation, the Office of Naval Research, and the Ohio Eminent Scholar Discretionary Fund. Partial support was provided by The Ohio State University Institute for Materials Research.