Influences of partial melting and overheating on amorphization of Ge2Sb2Te5 during the reset process

Abstract

It is very important to observe the change in the atomic structure of melt-quenched amorphous Ge2Sb2Te5 (GST) to discover the failure mechanism of phase-change random access memory (PRAM) devices during the reset process. We fabricated the phase-change devices and measured the initial resistance changes with various reset pulse amplitudes. For the observation of the atomic structure changes of GST thin films, we designed the specimens for transmission electron microscopy (TEM) and annealed them below and above the melting temperature of GST (Tm = 650 degrees C) before quenching. The annealed-and-quenched GST at 630 degrees C has a hexagonal structure with a grain size of about 10 nm after the partial melting. The annealed-and-quenched GST at 750 degrees C also has a hexagonal structure because of the latent heat. The observed atomic structures of GST are in accordance with the resistance changes inferred from the fabricated edge-contact type of PRAM cell. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim