Zhitang Song

Phase Change and Memory

Shanghai Institute of Microsystem and Information Technology, Shanghai, China

Email: ztsong@mail.sim.ac.cn

Biography

      Zhitang Song, Professor of Shanghai Institute of Microsystem and Information Technology (SIMIT), National Ten Thousands talent, Chief Scientist of National Super 973. He received PhD in Engineering from Xi'an Jiaotong University in 1997, and worked as a post doctor in Shanghai Institute of Microsystems (SIMIT) in 1998. 
Since 2002, he have been worked on Phase Change Materials, Phase Change Memory (PCM) and CMP Slurry. He developed the first PCM chip in China, and embedded chips with 15 million sales volume which was first applied in the world. He proposed the robust octahedral configuration phase change theory and discovered crystal-liquid-crystal switching mechanism, and published more than 600 papers in SCI journals, including Sciences (2 papers), Nature Communications (5 papers), and IEDM (3 papers), and applied 365 domestic authorized invention patents. As Chief Scientist and Project Director of National Integrate Circuit Research Program (02 special subject) and National Program on Key Basic Research Project 973 (Class A) of China, he has undertaken more than 50 national or provincial research projects: "Strategic Priority Research Program" of the Chinese Academy of Sciences, National High-tech R&D Program of China (863), National Natural Science Foundation of China, etc. 
He won the 2020 First Prize of Shanghai Natural Science Award, 2016 Fist Prize of Shanghai Technological Invention Award, 2018 Second Prize of Shanghai Technological Invention Award, 2021 Huawei OlympusMons Pioneer Award and so on. 

Abstract for Presentation

High Density Phase Change Memory

    Phase change memory (PCM) has been successfully applied in the computer storage architecture, as storage class memory, to bridge the performance gap between DRAM and Flash-based solid-state drive due to its good scalability, high density, fast operation speed and compatible with CMOS technology. A good understanding of phase change mechanism is of great help to design new phase change materials with fast operation speed, low power consumption and long-lifetime. In this presentation, we firstly review the development of PCM and different understandings on phase change mechanisms in recent years, and then propose a new view on the mechanism, which is based on the octahedral structure motifs and vacancies. Based on the octahedral phase change mechanism, we introduced Sc-based robust octahedra in Sb2Te3 phase change materials, called Sc-Sb-Te, and achieved 700 ps operation speed [1]. Focusing on phase change materials and PCM for decades, we have successfully developed 128Mb embedded PCM chips, which can meet the requirements of most embedded systems.

To achieve high density PCM, cross-point architecture is needed, which consisted of one memory cell and one switch cell, thereby further density scaling below10 nanometers requires compositionally and structurally homogeneous materials for both the memory cell and the associated vertically stacked two-terminal access switch. We present a single-element tellurium (Te) volatile switch with a large (≥11 megaamperes per square centimeter) drive current density, ~103 ON/OFF current ratio, and faster than 20 nanosecond switching speed [2]. The low OFF current arises from the existence of a ~0.95–electron volt Schottky barrier at the Te–electrode interface, whereas a transient, voltage pulse–induced crystal-liquid melting transition of the pure Te leads to a high ON current. Our discovery of a single-element electrical switch may help realize denser PCM chips.

References

[1] F. Rao*, K. Ding, Y. Zhou, Y. Zheng, M. Xia, S. Lv, Z. Song*, S. Feng, I. Ronneberger, R. Mazzarello, W. Zhang*, Evan Ma, Science, 358 (2017), 1423.

[2] J. Shen, S. Jia, N. Shi, Q. Ge, T. Gotoh, S. Lv, QLiu, R. Dronskowski, S. R. Elliott, Z. Song*, M. Zhu*, Science, 374 (2021), 1390.