The State Key Lab of
High Performance Ceramics and Superfine Microstructure
Shanghai Institute of Ceramics, Chinese Academy of Sciences
中 国 科 学 院 上 海 硅 酸 盐 研 究 所 高 性 能 陶 瓷 和 超 微 结 构 国 家 重 点 实 验 室
Recent development in phase change memory materials using time-dependent density functional theory
Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, 12180, USA
报告摘要： Phase change memory (PCM) materials exhibit fascinating physics as SET (i.e., its amorphiszation) happens in less than a 100 fs, while RESET (i.e., its recrystallization) happens in a matter of only a few ns, which defies exclusively all the phase-change phenomena known for solid state. They are the backbone of DVD, as well as that of electronic memory devices such as IBM’s storage class memory and the recent Micron’s X-Point technology. Most recently, PCM also gained momentum for developing non-von Neumann architecture, beyond CMOS, and in-memory computing. Our journey on the quest of the PCM materials started with the understanding of phase transitions using static and quasi-static first-principles calculations. Nonetheless, a non-thermal nature of the ultrafast PCM material amorphization under a high electronic excitation was unveiled for the first time, which has since gained considerable momentum. Using the recently developed time-dependent density functional theory (TDDFT)-molecular dynamics (MD), we not only confirmed the previous predictions, but also uncovered the dependence on the excitation energies – a high enough excitation energy inevitably leads to a significant carrier multiplication effect. As such, a phase transition takes place well before the lattice can be heated up. A similar phenomenon found in standard semiconductors, coined with the name plasma quenching, was also explained by our theory. Most recently, we found that, in ferroelectric materials, an equally ultrafast (< a few 100’s fs) phases transition can take place between crystalline phases. While this proposition is in startle contrast to our na？ve intuition, it is in full agreement with experiments.
Shengbai Zhang graduated from Jilin University in 1982. He received Ph.D. in Physics from the University of California at Berkeley in 1989. He moved to Xerox PARC as a postdoc, before joining the National Renewable Energy Laboratory in 1991. In 2008, he became the Senior Kodosky Constellation Chair and Professor in Physics at Rensselaer Polytechnic Institute. His computational research covers a wide range of materials for bulk properties, defect structures, and surface physics. His recent work involves emerging low-cost photovoltaic materials, phase change memory materials, topological insulators, Weyl semimetals, two-dimensional layered materials, and excited state dynamics. He has published ~390 peer-reviewed articles, including 60 in Physical Review Letters, with a total citation over 25,000. He is a Fellow of the American Physical Society since 2001.