[en] Ag-doped Sb–Te films were deposited by magnetron co-sputtering and the structure, electrical, optical and thermal properties were analyzed. The results show that Ag-doping restrains crystal grain size, and changes a preferred orientation of the crystalline phase. The crystallization temperature is increased due to the Ag addition. Both amorphous resistance and crystalline resistance are enhanced and the resistance ratio reaches ∼10⁴. Compared with Ge₂Sb₂Te₅, Ag_26.82(Sb₃Te)_73.18 film exhibits a better amorphous thermal stability, a higher crystallization temperature (∼166 °C), a wider optical band gap (0.515 eV), a larger crystallization activation energy (3.17 eV) as well as a better 10 years data retention at 92 °C. (paper)

[en] Highlights: • The phase change behavior of GeTe/Sb₄Te was studied for multilevel storage. • A multilevel storage can be realized with various appropriate thickness ratios. • A multilevel storage can be achieved by electrical pulse as short as 5 ns. - Abstract: In this paper, GeTe and Sb₄Te layers were alternately deposited to form superlattice-like structure (SLL) for multilevel phase change memory (PCM). It is shown that SLL GeTe/Sb₄Te film can realize a multilevel storage with various appropriate thickness ratios between GeTe and Sb₄Te layers. The crystallization behavior of SLL GeTe/Sb₄Te film can be tuned by the thickness ratios which is associated closely with the thermal stability. GeTe(4 nm)/Sb₄Te(6 nm)-based device demonstrated the minimum voltage pulse for the RESET operation of 3.2 V-5 ns, suggesting the low power consumption in comparison with that of Ge₂Sb₂Te₅ (4.1 V). An electric pulse as short as 5 ns can trigger different operations among three stable resistance states for GeTe(4 nm)/Sb₄Te(6 nm)-based device, which can be explained by the asynchronous crystallization of GeTe and Sb₄Te. These results demonstrate that SLL GeTe/Sb₄Te films are promising candidate for multilevel phase-change memory.