A phase change for high-density data storage
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. (
