Computer-simulation design of new phase-change memory materials

Phase-change (PC) materials are being developed for a new non-volatile electronic-memory technology to replace flash memory. Fast, reversible transformations between amorphous and crystalline states (with different electrical resistivities, thereby encoding bits of information) are produced by appropriate voltage pulses. Existing PC materials, such as Ge-Sb-Te compounds, have so far been developed empirically. We present the first design, in silico, of a simulated new PC material, whose (cubic) crystal structure, and electrical-resistivity level, has been predetermined. Heterogeneous crystallization of PC memory cells has been reproduced by ab initio molecular-dynamics simulation for the first time. We show how an optimal choice of cell boundaries can drastically speed up crystallization and enhance resistivity contrast. This optimization method opens up a yet unexplored dimension of the study of PC materials. The present computational approach offers a route for the efficient discovery of ultrafast PC materials that could even replace DRAM. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim