Atomic scale insight into the effects of Aluminum doped Sb2Te for phase change memory application

First-principles study of the liquid and amorphous phases of Sb2Te phase change memory material

We have investigated the local structure of liquid and amorphous phases of Sb₂Te phase change memory material by the means of density functional theory-molecular dynamics simulations. The models of liquid and amorphous states were generated by quenching from the melt. The results show that the local environment of liquid Sb₂Te is a mixed bonding geometry, where the average coordination numbers (CNs) of Sb and Te atoms are 4.93 and 4.23, respectively. Compared with crystalline state, there are more Sb-Sb bonds (∼53%) and less Sb-Te bonds (∼42%) with the presence of Te-Te bonds (∼5%) in liquid Sb₂Te. Therefore, the formation of homopolar bonds and the breaking of heteropolar bonds are important structural transformations in melt process. For amorphous Sb₂Te, the average CNs of Sb and Te atoms are 4.54 and 3.57, respectively. They are mostly in an octahedral environment, similar to the case in crystalline phase. The fractions of Sb-Sb, Te-Te, and Sb-Te bonds are ∼52%, ∼2%, and ∼46%, respectively. Thus, the increase in the fraction of octahedron accompanied with the decrease in average CN is the major structural changes in quenching process. Furthermore, the octahedral geometry in both the crystalline and amorphous Sb₂Te increases the local structural similarity, facilitating the rapid low-energy crystallization.

Ta-Doped Sb2Te Allows Ultrafast Phase-Change Memory with Excellent High-Temperature Operation Characteristics

Phase-change memory (PCM) has considerable promise for new applications based on von Neumann and emerging neuromorphic computing systems. However, a key challenge in harnessing the advantages of PCM devices is achieving high-speed operation of these devices at elevated temperatures, which is critical for the efficient processing and reliable storage of data at full capacity. Herein, we report a novel PCM device based on Ta-doped antimony telluride (Sb₂Te), which exhibits both high-speed characteristics and excellent high-temperature characteristics, with an operation speed of 2 ns, endurance of > 10⁶ cycles, and reversible switching at 140 °C. The high coordination number of Ta and the strong bonds between Ta and Sb/Te atoms contribute to the robustness of the amorphous structure, which improves the thermal stability. Furthermore, the small grains in the three-dimensional limit lead to an increased energy efficiency and a reduced risk of layer segregation, reducing the power consumption and improving the long-term endurance. Our findings for this new Ta-Sb₂Te material system can facilitate the development of PCMs with improved performance and novel applications.