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Research Communications

Physicist David Drabold aims to improve efficiency in electronics 

By Philip Barnes 

Feb. 18, 2013

Physicist David Drabold is looking for ways to make computer memory faster, and thinks that silver could be the key to speed.

In a new paper published in Applied Physics Letters, the Ohio University Distinguished Professor of Physics and his research team propose adding small amounts of silver to improve non-volatile "phase change" flash memory, which allows electronic devices to store information even when powered off.

"There are two components to the phases: amorphous and crystalline," Drabold says. "If you can reduce the amount of time it takes to get from one to the other, you can ultimately improve things like download speed and overall performance in a real device."

Graduate student Binay Prasai
and Assistant Professor of Physics and Astronomy Gang Chen have been working with Drabold to better understand the relationship between amorphous and crystalline structures. During a phase change, an electrical heat source melts the cube-like crystalline structure into an amorphous state, where atoms are arranged at random, making their positions and movements difficult to predict.

 drabold image
Images of phase change materials: a) and c) are the computed amorphous and crystalline phases of conventional material; b) and d) are similar but with 5 percent silver. The silver (grey) atoms fit substitutionally into the cubic crystalline phase. (Images courtesy of David Drabold.)

Over a few hundred picoseconds (1 picosecond equals 10-12 sec), Drabold and his colleagues can simulate heating the amorphous structure,  causing it to return to a crystalline phase. Conventional memory storage is based upon a binary 0 or 1 convention to store information. For phase change materials, binary information is represented by the structural phase, amorphous or crystalline.

Through quantum mechanical simulations, Drabold found that "doping" the standard phase change materials (germanium, antimony and tellurium) with silver increases the transition speed from amorphous to crystalline. Stability remains intact. Similar materials are used in some DVDs, he notes.

"The workhorse program we use is called VASP, the Vienna Ab initio Simulation Package. It allows us to observe the energies, forces and  atomic properties, as well as directly simulate phase changes while accurately handling the complex chemistry," he says.

The study was funded by two grants from the National Science Foundation and used computing time at the Ohio Supercomputer Center in Columbus.
 David Drabold
David Drabold

Next, Drabold's team will seek to understand and document more about the process so that it can be carried out in laboratory experiments.

"It is extremely expensive to run these tests in a lab, so we need to figure out why silver works," says Drabold, who is seeking additional National Science Foundation funding for the project.

The scientist's ultimate goal goes hand-in-hand with President Obama's Materials Genome Initiative—which aims to support U.S. scientific innovation and technology development in part by developing the computational prediction of materials.

"Eventually, I want to use computational materials design to predict new, more efficient materials," Drabold says. "I want to be able to say, 'You should make the glass in your car with this or the wings on a jet out of this. With some initial computational guidance, a company could develop the material more quickly and cheaply, and give the United States a competitive advantage."