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A phase change for high-density data storage

MAR 01, 2005

DOI: 10.1063/1.2405563

Using electron beams instead of optical beams, scientists at Hewlett Packard have read individual, rewritable bits in a thin indium–selenium layer. That layer, a buffer layer of gallium–selenium, and a silicon substrate, form the principal parts of a pn-junction diode. The read–write cycle goes like this: Short, high-power bursts from an electron beam are used to write a 1 by melting and quenching a small region of the InSe surface and turning it from a crystalline to a glassy phase. The amorphous blob can be erased by the use of a longer, lower-power beam pulse. Raised just above the crystallization temperature, the InSe recrystallizes, apparently by regrowing epitaxially from the surrounding crystal matrix. A beam pulse of still lower power can read the bit as either a 1 (the amorphous blob yields little or no detectable current in the pn-junction diode) or a 0 (the crystalline material yields a high diode current). Thus far, the HP researchers have written with a laser beam rather than an electron beam (their electron beam isn’t yet strong enough), but they have employed an e-beam for reading and erasing. The phase-change medium can respond to reading rates of at least a million bits per second per electron beam, and more than 100 write-erase-rewrite cycles have been carried out successfully on single bits. The researchers hope to reduce the bit size from its current 150 nm across to perhaps 10 nm. (G. A. Gibson et al. , Appl. Phys. Lett. 86, 051902, 2005.http://dx.doi.org/10.1063/1.1856690 )

This Content Appeared In
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Volume 58, Number 3

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