RESEARCHERS TO BUILD NOVEL SPINTRONICS INSTRUMENT TO MAKE A BETTER TRANSISTOR

FAYETTEVILLE, Ark. — Transistors, miniature electronic switches that power televisions, cars, radios, home appliances and computers, will soon reach limitations in their ability to perform calculations quickly. A group of University of Arkansas researchers has won a grant to build an instrument that may create the next generation of transistors that are faster and more efficient than current ones.

Paul Thibado, associate professor of physics at the University of Arkansas, Vincent LaBella, assistant professor of physics at SUNY Albany, and postdoctoral research associate Dan W. Bullock have received a $750,000 Major Research Instrumentation grant from the National Science Foundation to build a novel instrument in the field of spintronics. This instrument may lead to the creation of the fastest transistor ever.

A traditional transistor consists of a source, a drain and a gate. When an electric field is placed on the gate, current moves from the source to the drain. Although this can be accomplished with great speed, it is limited by the speed of the electric current pulse.

For years, researchers have explored the possibility of building transistors that use an electron’s spin polarization as the driving force.

"It’s very easy and quick to change the orientation of an electron’s spin," LaBella said. An electron’s spin can change almost instantaneously by applying a magnetic field to the gate.

Physicists hope to harness the power of an electron’s spin to make multifunctional computational devices, where a single multifunctional device would replace hundreds of conventional devices, leading to faster, smaller electronics that consume less power.

Currently, electronic devices use an electron’s mass and charge to do the necessary work, but these devices have limitations in their size and power-researchers estimate that in about 10 years the prevalent technologies used today to make smaller, more powerful devices will reach that limit.

For about 10 years, researchers have been exploring the idea of exploiting an electron’s spin to enhance the performance of devices. Spins can rotate in a coherent manner and thus alter the resistance of a device in a controlled manner. These properties may enable greater storage capacity and information processing from spintronic devices.

So far, however, a spin-polarized transistor has remained a theory, because until recently no one has been able to inject spin-polarized electrons into a semiconducting surface with great efficiency.

Last year, however, the University of Arkansas team achieved injection efficiency of 92 percent into a gallium arsenide (GaAs 110) surface at a temperature of 100 K, which is the temperature of liquid nitrogen, a substance often used in the semiconductor industry. They reported their findings in the May 25, 2001, issue of Science.

Building on that work, the researchers plan to build a spin transistor using a scanning tunneling microscope as the injector for spin-polarized electrons. They intend to build a dual-tip scanning tunneling microscope, using the two tips in close proximity to one another, coming in at different angles to the atomic surface.

One tip will be used to inject electrons of a certain spin, while the other acts as a detection device, reading the actual spin of the injected electrons. By applying a magnetic field, the researchers can then change the electrons’ spins, creating a field-effect transistor.

The researchers will use computer-operated nano-positioning systems to move the tips with nanoscale precision.

The NSF grant will allow the researchers to purchase a vacuum chamber, a scanning tunneling microscope and an extra STM tip. The researchers will build the instrument from scratch.

It will take up to three years to build and test the instrument.