Material promises denser DVDs

March 9/16, 2005

One of the perennial challenges in making more information fit in the same amount of space is finding a way to make smaller bits, or areas of materials that can represent the 1s and 0s of computer information.

Researchers from Hewlett-Packard Laboratories and Lawrence Berkeley National Lab have found a way to use electron beams to read, write and erase bits. Electron beams have much smaller wavelengths than the lightwaves currently used by optical storage devices like compact discs, and can therefore use smaller areas of storage media as bits.

The technology could lead to high-speed, ultrahigh density storage media; the material at the heart of the technology could also be used in solar cells, according to the researchers.

The researchers made their prototype by causing diodes to form in a layer of indium selenium and a layer of gallium selenium on a silicon chip. A diode allows current flow in one direction but not the other.

A bit of information is written to the diode layer by aiming a brief blast from a high-power electron beam to make a tiny glassy blob. A longer, low-power pulse recrystallizes the material to erase the bit. And a very-low-power pulse senses whether a certain spot is a glassy blob or not because the glassy blob does not return a detectable current but the crystallized material does.

Key to the process is that the layered diode material maintains its electrical properties even after repeated cycles of melting and recrystallization.

The technology has the potential to read bits that are as small as 50 nanometers in diameter, and perhaps as small as 10 nanometers, according to the researchers. A nanometer is one millionth of a millimeter. The dot size on today's DVDs is 740 by 400 nanometers.

The memory could be used in practical applications in two to three years, according to the researchers. The work appeared in the January 31, 2005 issue of Applied Physics Letters.

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