The Ge2Sb2Te5 alloy has served as the core material in phase-change memories with high switching speed and persistent storage capability at room temperature. However widely used, this composition is not suitable for embedded memories—for example, for automotive applications, which require very high working temperatures above 300 °C. Ge–Sb–Te alloys with higher Ge content, most prominently Ge2Sb1Te2 (‘212’), have been studied as suitable alternatives, but their atomic structures and structure–property relationships have remained widely unexplored. Here, we report comprehensive first-principles simulations that give insight into those emerging materials, located on the compositional tie-line between Ge2Sb1Te2 and elemental Ge, allowing for a direct comparison with the established Ge2Sb2Te5 material. Electronic-structure computations and smooth overlap of atomic positions (SOAP) similarity analyses explain the role of excess Ge content in the amorphous phases. Together with energetic analyses, a compositional threshold is identified for the viability of a homogeneous amorphous phase (‘zero bit’), which is required for memory applications. Based on the acquired knowledge at the atomic scale, we provide a materials design strategy for high-performance embedded phase-change memories with balanced speed and stability, as well as potentially good cycling capability.
Thermal stability and phase separation tendency of Ge-Sb-Te alloys
Link to the article: https://www.nature.com/articles/s41524-021-00496-7
This work is done by Prof. Wei Zhang and co-workers at Xi’an Jiaotong University and Xi’an Shiyou University. Other contributors include Prof. Volker L. Deringer at Oxford University and Prof. Riccardo Mazzarello at Sapienza University of Rome. Prof. Zhang’s group is a part of Center for Alloy Innovation and Design at XJTU, focusing on the investigations of phase-change materials for advanced memory and neuromorphic computing applications. Prof. Zhang hosts international students for degree programs and short-term visits regularly. He could be reached via wzhang0@mail.xjtu.edu.cn More information can be found at http://gr.xjtu.edu.cn/en/web/wzhang0/home.
