Researchers move a step closer to faster electronics

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Posted: Sunday, February 24, 2013 12:00 am

LINCOLN — Researchers at the University of Nebraska-Lincoln have taken a major step toward breaking the “silicon barrier,” demonstrating that a new material only a few atoms thick could be used to store more digital information while using less energy than silicon-based memory.

With the ability to improve silicon transistors reaching the fundamental limit, researchers around the world have been hunting for new ways to make faster and more powerful electronic devices.

UNL physicist Evgeny Tsymbal and his colleagues have demonstrated that a “nanostructure” — in this case, a very thin layer of ferroelectric oxide — may hold the key. Their latest findings were published last week in an online edition of Nature Materials.

Using quantum theories and supercomputers at UNL's Holland Center, Tsymbal and colleague John D. Burton predicted how a ferroelectric memory element would behave.

They then asked that their theory be tested by experimentalist Qi Li at Penn State University, UNL physicist Alexei Gruverman and other colleagues at Oak Ridge National Laboratory in Tennessee and universities in Korea and China. The experiments proved the researchers' predictions correct.

The theory is based, in, part, on a phenomenon called quantum tunneling, in which particles can pass through a barrier only at the quantum, or atomic, level. To develop a new generation of electronics, scientists are experimenting with tunnel junctions, in which an ultra-thin barrier is placed between two electrodes. When voltage is applied, electrons tunnel through the barrier, which creates a current with resistance.

Tsymbal and his colleagues created a tunnel junction using the nano-thin ferroelectric oxide, a material with both positive and negative polarization directions, which can be reversed by switching the voltage charge. Reversing the polarization creates a measurable change in resistance through the tunnel junction.

Those properties would allow scientists to detect the changes in polarization and to use the two directions as a binary code to store information. A ferroelectric device could be smaller than current silicon-based devices because it would use less energy and need less space to accommodate the heat generated by larger currents.

Such devices won't be available to the general public any time soon. So far, the effects found by the scientists occur only at extremely low temperatures — 100 degrees below zero Fahrenheit.

“For applications, you obviously want to have this change in resistance at room temperature,” Tsymbal said. “This can't be used immediately, but it shows some new directions to pursue.”

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