JOHNS HOPKINS (US) — Engineers have uncovered new electrical properties of a material used in computer memory by applying pressure with diamond-tipped tools.
The discovery opens the door to more durable drives, discs, and computer systems that absorb more data more quickly, researchers say.
The research focused on an inexpensive phase-change memory alloy called GST, composed of germanium, antimony, and tellurium. The material is already commonly used in rewritable optical media, including CD-RW and DVD-RW discs.
“This phase-change memory is more stable than the material used in the current flash drives. It works 100 times faster and is rewritable about 100,000 times,” says lead author Ming Xu, a doctoral student in materials science and engineering at Johns Hopkins University. “Within about five years, it could also be used to replace hard drives in computers and give them more memory.”
The work was reported in the online edition of Proceedings of the National Academy of Sciences.
GST is called a phase-change material because, when exposed to heat, it can change from an amorphous state, in which the atoms lack an ordered arrangement, to a crystalline state, in which the atoms are neatly lined up in a long-range order.
In its amorphous state, GST is more resistant to electric current. In its crystalline state, it is less resistant. The two phases also reflect light differently, allowing the surface of a DVD to be read by a tiny laser. The two states correspond to one and zero, the alphabet of computer language.
Although this phase-change material has been used for at least two decades, the precise mechanics of this switch from one state to another have remained something of a mystery because it happens so quickly—in nanoseconds—when the material is heated.
To solve this mystery, Xu and his team used another method to trigger the change more gradually. Instead of heat, the researchers used two diamond tips to compress the material. They employed a process called X-ray diffraction and a computer simulation to document what was happening to the material at the atomic level.
The researchers found they could “tune” the electrical resistivity of the material during its slower changeover from amorphous to crystalline form.
“Instead of going from black to white, it’s like finding shades or a shade of gray in between,” says Xu’s doctoral adviser, En Ma, professor of materials science and engineering and a co-author of the PNAS paper. “By having a wide range of resistance, you can have a lot more control. If you have multiple states, you can store a lot more data.”
Other co-authors of the paper were from Johns Hopkins, Oak Ridge National Laboratory, the Carnegie Institution of Washington, George Mason University and Beijing University of Technology. Funding for the research was provided by the U.S. Department of Energy, the Office of Naval Research, the Chinese National Basic Research Program, the National Science Foundation, the W. M. Keck Foundation and Argonne National Laboratory.
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