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Kang L, Chen L. First-principles study of the liquid and amorphous phases of Sb 2Te phase change memory material. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:165703. [PMID: 33740774 DOI: 10.1088/1361-648x/abf077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2021] [Accepted: 03/19/2021] [Indexed: 06/12/2023]
Abstract
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.
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Affiliation(s)
- Lei Kang
- School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, People's Republic of China
| | - Leng Chen
- School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, People's Republic of China
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Guo YR, Dong F, Qiao C, Wang JJ, Wang SY, Xu M, Zheng YX, Zhang RJ, Chen LY, Wang CZ, Ho KM. Structural signature and transition dynamics of Sb2Te3 melt upon fast cooling. Phys Chem Chem Phys 2018; 20:11768-11775. [DOI: 10.1039/c8cp00142a] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Sb-centered defective octahedrons connect with each other via four-fold rings, a close link of the four-fold ring and defective octahedrons in amorphous Sb2Te3 has been revealed.
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Affiliation(s)
- Y. R. Guo
- Shanghai Ultra-Precision Optical Manufacturing Engineering Center and Department of Optical Science and Engineering, Fudan University
- Shanghai
- China
| | - F. Dong
- Shanghai Ultra-Precision Optical Manufacturing Engineering Center and Department of Optical Science and Engineering, Fudan University
- Shanghai
- China
| | - C. Qiao
- Shanghai Ultra-Precision Optical Manufacturing Engineering Center and Department of Optical Science and Engineering, Fudan University
- Shanghai
- China
| | - J. J. Wang
- Shanghai Ultra-Precision Optical Manufacturing Engineering Center and Department of Optical Science and Engineering, Fudan University
- Shanghai
- China
| | - S. Y. Wang
- Shanghai Ultra-Precision Optical Manufacturing Engineering Center and Department of Optical Science and Engineering, Fudan University
- Shanghai
- China
- Key Laboratory for Information Science of Electromagnetic Waves (MoE)
- Shanghai 200433
| | - Ming Xu
- School of Optical & Electronic Information, Huazhong University of Science & Technology
- Wuhan
- China
| | - Y. X. Zheng
- Shanghai Ultra-Precision Optical Manufacturing Engineering Center and Department of Optical Science and Engineering, Fudan University
- Shanghai
- China
| | - R. J. Zhang
- Shanghai Ultra-Precision Optical Manufacturing Engineering Center and Department of Optical Science and Engineering, Fudan University
- Shanghai
- China
| | - L. Y. Chen
- Shanghai Ultra-Precision Optical Manufacturing Engineering Center and Department of Optical Science and Engineering, Fudan University
- Shanghai
- China
| | - C. Z. Wang
- Ames Laboratory, U. S. Department of Energy and Department of Physics and Astronomy, Iowa State University
- Ames
- USA
| | - K. M. Ho
- Ames Laboratory, U. S. Department of Energy and Department of Physics and Astronomy, Iowa State University
- Ames
- USA
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Rao F, Ding K, Zhou Y, Zheng Y, Xia M, Lv S, Song Z, Feng S, Ronneberger I, Mazzarello R, Zhang W, Ma E. Reducing the stochasticity of crystal nucleation to enable subnanosecond memory writing. Science 2017; 358:1423-1427. [PMID: 29123020 DOI: 10.1126/science.aao3212] [Citation(s) in RCA: 132] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Accepted: 10/30/2017] [Indexed: 01/26/2023]
Abstract
Operation speed is a key challenge in phase-change random-access memory (PCRAM) technology, especially for achieving subnanosecond high-speed cache memory. Commercialized PCRAM products are limited by the tens of nanoseconds writing speed, originating from the stochastic crystal nucleation during the crystallization of amorphous germanium antimony telluride (Ge2Sb2Te5). Here, we demonstrate an alloying strategy to speed up the crystallization kinetics. The scandium antimony telluride (Sc0.2Sb2Te3) compound that we designed allows a writing speed of only 700 picoseconds without preprogramming in a large conventional PCRAM device. This ultrafast crystallization stems from the reduced stochasticity of nucleation through geometrically matched and robust scandium telluride (ScTe) chemical bonds that stabilize crystal precursors in the amorphous state. Controlling nucleation through alloy design paves the way for the development of cache-type PCRAM technology to boost the working efficiency of computing systems.
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Affiliation(s)
- Feng Rao
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-system and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China.,College of Materials Science and Engineering, Shenzhen University, Shenzhen 518060, China
| | - Keyuan Ding
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-system and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China.,College of Materials Science and Engineering, Shenzhen University, Shenzhen 518060, China
| | - Yuxing Zhou
- Center for Advancing Materials Performance from the Nanoscale, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China
| | - Yonghui Zheng
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-system and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Mengjiao Xia
- International Laboratory of Quantum Functional Materials of Henan, School of Physics and Engineering, Zhengzhou University, Zhengzhou 450001, China
| | - Shilong Lv
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-system and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Zhitang Song
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-system and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China.
| | - Songlin Feng
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-system and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Ider Ronneberger
- Institute for Theoretical Solid State Physics, JARA-FIT and JARA-HPC, RWTH Aachen University, Aachen D-52074, Germany
| | - Riccardo Mazzarello
- Institute for Theoretical Solid State Physics, JARA-FIT and JARA-HPC, RWTH Aachen University, Aachen D-52074, Germany
| | - Wei Zhang
- Center for Advancing Materials Performance from the Nanoscale, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China
| | - Evan Ma
- Center for Advancing Materials Performance from the Nanoscale, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China.,Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, MD 21218, USA
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Zhang W, Ronneberger I, Zalden P, Xu M, Salinga M, Wuttig M, Mazzarello R. How fragility makes phase-change data storage robust: insights from ab initio simulations. Sci Rep 2014; 4:6529. [PMID: 25284316 PMCID: PMC4185410 DOI: 10.1038/srep06529] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2014] [Accepted: 09/15/2014] [Indexed: 11/24/2022] Open
Abstract
Phase-change materials are technologically important due to their manifold applications in data storage. Here we report on ab initio molecular dynamics simulations of crystallization of the phase change material Ag4In3Sb67Te26 (AIST). We show that, at high temperature, the observed crystal growth mechanisms and crystallization speed are in good agreement with experimental data. We provide an in-depth understanding of the crystallization mechanisms at the atomic level. At temperatures below 550 K, the computed growth velocities are much higher than those obtained from time-resolved reflectivity measurements, due to large deviations in the diffusion coefficients. As a consequence of the high fragility of AIST, experimental diffusivities display a dramatic increase in activation energies and prefactors at temperatures below 550 K. This property is essential to ensure fast crystallization at high temperature and a stable amorphous state at low temperature. On the other hand, no such change in the temperature dependence of the diffusivity is observed in our simulations, down to 450 K. We also attribute this different behavior to the fragility of the system, in combination with the very fast quenching times employed in the simulations.
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Affiliation(s)
- Wei Zhang
- 1] Institute for Theoretical Solid State Physics, RWTH Aachen University, 52056 Aachen, Germany [2] I. Physikalisches Institut (IA), RWTH Aachen University, 52056 Aachen, Germany
| | - Ider Ronneberger
- Institute for Theoretical Solid State Physics, RWTH Aachen University, 52056 Aachen, Germany
| | - Peter Zalden
- 1] I. Physikalisches Institut (IA), RWTH Aachen University, 52056 Aachen, Germany [2] Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
| | - Ming Xu
- I. Physikalisches Institut (IA), RWTH Aachen University, 52056 Aachen, Germany
| | - Martin Salinga
- I. Physikalisches Institut (IA), RWTH Aachen University, 52056 Aachen, Germany
| | - Matthias Wuttig
- 1] I. Physikalisches Institut (IA), RWTH Aachen University, 52056 Aachen, Germany [2] JARA-FIT and JARA-HPC, RWTH Aachen University, 52056 Aachen, Germany
| | - Riccardo Mazzarello
- 1] Institute for Theoretical Solid State Physics, RWTH Aachen University, 52056 Aachen, Germany [2] JARA-FIT and JARA-HPC, RWTH Aachen University, 52056 Aachen, Germany
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