The present invention relates to a phase-change memory device structure and the materials used. The structure comprises a substrate, a single or multiple sandwich-memory-unit(s), a first electrode, and a second electrode. The sandwich-memory-unit contains an upper barrier layer, a lower barrier layer, and a memory layer therebetween. The thickness of the memory-layer is less than 30 nm. The present invention provides a phase-change memory device with a high Tc and a low volume changing rate during phase-change.