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
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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