1
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Manjón FJ, Osman HH, Savastano M, Vegas Á. Electron-Deficient Multicenter Bonding in Phase Change Materials: A Chance for Reconciliation. MATERIALS (BASEL, SWITZERLAND) 2024; 17:2840. [PMID: 38930210 PMCID: PMC11204841 DOI: 10.3390/ma17122840] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2024] [Revised: 06/03/2024] [Accepted: 06/06/2024] [Indexed: 06/28/2024]
Abstract
In the last few years, a controversy has been raised regarding the nature of the chemical bonding present in phase change materials (PCMs), many of which are minerals such as galena (PbS), clausthalite (PbSe), and altaite (PbTe). Two opposite bonding models have claimed to be able to explain the extraordinary properties of PCMs in the last decade: the hypervalent (electron-rich multicenter) bonding model and the metavalent (electron-deficient) bonding model. In this context, a third bonding model, the electron-deficient multicenter bonding model, has been recently added. In this work, we comment on the pros and cons of the hypervalent and metavalent bonding models and briefly review the three approaches. We suggest that both hypervalent and metavalent bonding models can be reconciled with the third way, which considers that PCMs are governed by electron-deficient multicenter bonds. To help supporters of the metavalent and hypervalent bonding model to change their minds, we have commented on the chemical bonding in GeSe and SnSe under pressure and in several polyiodides with different sizes and geometries.
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Affiliation(s)
- Francisco Javier Manjón
- Instituto de Diseño para la Fabricación y Producción Automatizada, MALTA Consolider Team, Universitat Politècnica de València, 46022 Valencia, Spain;
| | - Hussien H. Osman
- Instituto de Diseño para la Fabricación y Producción Automatizada, MALTA Consolider Team, Universitat Politècnica de València, 46022 Valencia, Spain;
- Instituto de Ciencia de los Materiales de la Universitat de València, MALTA Consolider Team, Universitat de València, 46100 Valencia, Spain
- Chemistry Department, Faculty of Science, Helwan University, Cairo 11795, Egypt
| | - Matteo Savastano
- Department of Human Sciences for the Promotion of Quality of Life, University San Raffaele Roma, via di Val Cannuta 247, 00166 Rome, Italy;
| | - Ángel Vegas
- Universidad de Burgos, Hospital del Rey, 09001 Burgos, Spain;
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2
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Zhao Z, Clima S, Garbin D, Degraeve R, Pourtois G, Song Z, Zhu M. Chalcogenide Ovonic Threshold Switching Selector. NANO-MICRO LETTERS 2024; 16:81. [PMID: 38206440 PMCID: PMC10784450 DOI: 10.1007/s40820-023-01289-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2023] [Accepted: 11/14/2023] [Indexed: 01/12/2024]
Abstract
Today's explosion of data urgently requires memory technologies capable of storing large volumes of data in shorter time frames, a feat unattainable with Flash or DRAM. Intel Optane, commonly referred to as three-dimensional phase change memory, stands out as one of the most promising candidates. The Optane with cross-point architecture is constructed through layering a storage element and a selector known as the ovonic threshold switch (OTS). The OTS device, which employs chalcogenide film, has thereby gathered increased attention in recent years. In this paper, we begin by providing a brief introduction to the discovery process of the OTS phenomenon. Subsequently, we summarize the key electrical parameters of OTS devices and delve into recent explorations of OTS materials, which are categorized as Se-based, Te-based, and S-based material systems. Furthermore, we discuss various models for the OTS switching mechanism, including field-induced nucleation model, as well as several carrier injection models. Additionally, we review the progress and innovations in OTS mechanism research. Finally, we highlight the successful application of OTS devices in three-dimensional high-density memory and offer insights into their promising performance and extensive prospects in emerging applications, such as self-selecting memory and neuromorphic computing.
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Affiliation(s)
- Zihao Zhao
- National Key Laboratory of Materials for Integrated Circuits, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, 200050, People's Republic of China
- University of Chinese Academy of Sciences, Beijing, 100029, People's Republic of China
| | | | | | | | | | - Zhitang Song
- National Key Laboratory of Materials for Integrated Circuits, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, 200050, People's Republic of China
| | - Min Zhu
- National Key Laboratory of Materials for Integrated Circuits, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, 200050, People's Republic of China.
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3
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Chen B, Wang X, Jiao F, Ning L, Huang J, Xie J, Zhang S, Li X, Rao F. Suppressing Structural Relaxation in Nanoscale Antimony to Enable Ultralow-Drift Phase-Change Memory Applications. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2023; 10:e2301043. [PMID: 37377084 PMCID: PMC10477879 DOI: 10.1002/advs.202301043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2023] [Revised: 06/05/2023] [Indexed: 06/29/2023]
Abstract
Phase-change random-access memory (PCRAM) devices suffer from pronounced resistance drift originating from considerable structural relaxation of phase-change materials (PCMs), which hinders current developments of high-capacity memory and high-parallelism computing that both need reliable multibit programming. This work realizes that compositional simplification and geometrical miniaturization of traditional GeSbTe-like PCMs are feasible routes to suppress relaxation. While to date, the aging mechanisms of the simplest PCM, Sb, at nanoscale, have not yet been unveiled. Here, this work demonstrates that in an optimal thickness of only 4 nm, the thin Sb film can enable a precise multilevel programming with ultralow resistance drift coefficients, in a regime of ≈10-4 -10-3 . This advancement is mainly owed to the slightly changed Peierls distortion in Sb and the less-distorted octahedral-like atomic configurations across the Sb/SiO2 interfaces. This work highlights a new indispensable approach, interfacial regulation of nanoscale PCMs, for pursuing ultimately reliable resistance control in aggressively-miniaturized PCRAM devices, to boost the storage and computing efficiencies substantially.
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Affiliation(s)
- Bin Chen
- College of Materials Science and EngineeringShenzhen Key Laboratory of New Information Display and Storage MaterialsShenzhen UniversityShenzhen518060China
| | - Xue‐Peng Wang
- College of Materials Science and EngineeringShenzhen Key Laboratory of New Information Display and Storage MaterialsShenzhen UniversityShenzhen518060China
- State Key Laboratory of Integrated OptoelectronicsCollege of Electronic Science and EngineeringJilin UniversityChangchun130012China
| | - Fangying Jiao
- College of Materials Science and EngineeringShenzhen Key Laboratory of New Information Display and Storage MaterialsShenzhen UniversityShenzhen518060China
| | - Long Ning
- College of Materials Science and EngineeringShenzhen Key Laboratory of New Information Display and Storage MaterialsShenzhen UniversityShenzhen518060China
| | - Jiaen Huang
- College of Materials Science and EngineeringShenzhen Key Laboratory of New Information Display and Storage MaterialsShenzhen UniversityShenzhen518060China
| | - Jiatao Xie
- College of Materials Science and EngineeringShenzhen Key Laboratory of New Information Display and Storage MaterialsShenzhen UniversityShenzhen518060China
| | - Shengbai Zhang
- Department of PhysicsApplied Physics, and AstronomyRensselaer Polytechnic InstituteTroyNY12180USA
| | - Xian‐Bin Li
- State Key Laboratory of Integrated OptoelectronicsCollege of Electronic Science and EngineeringJilin UniversityChangchun130012China
| | - Feng Rao
- College of Materials Science and EngineeringShenzhen Key Laboratory of New Information Display and Storage MaterialsShenzhen UniversityShenzhen518060China
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4
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Yang L, Tiwari SC, Fukushima S, Shimojo F, Kalia RK, Nakano A, Vashishta P, Branicio PS. Photoexcitation-Induced Nonthermal Ultrafast Loss of Long-Range Order in GeTe. J Phys Chem Lett 2022; 13:10230-10236. [PMID: 36300798 DOI: 10.1021/acs.jpclett.2c02448] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Nonadiabatic quantum molecular dynamics is used to investigate the evolution of GeTe photoexcited states. Results reveal a photoexcitation-induced picosecond nonthermal path for the loss of long-range order. A valence electron excitation threshold of 4% is found to trigger local disorder by switching Ge atoms from octahedral to tetrahedral sites and promoting Ge-Ge bonding. The resulting loss of long-range order for a higher valence electron excitation fraction is achieved without fulfilling the Lindemann criterion for melting, therefore utilizing a nonthermal path. The photoexcitation-induced structural disorder is accompanied by charge transfer from Te to Ge, Ge-Te bonding-to-antibonding, and Ge-Ge antibonding-to-bonding change, triggering Ge-Te bond breaking and promoting the formation of Ge-Ge wrong bonds. These results provide an electronic-structure basis to understand the photoexcitation-induced ultrafast changes in the structure and properties of GeTe and other phase-change materials.
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Affiliation(s)
- Liqiu Yang
- Collaboratory for Advanced Computing and Simulation, University of Southern California, Los Angeles, California 90089, United States
| | - Subodh C Tiwari
- Collaboratory for Advanced Computing and Simulation, University of Southern California, Los Angeles, California 90089, United States
| | - Shogo Fukushima
- Department of Physics, Kumamoto University, Kumamoto 860-8555, Japan
| | - Fuyuki Shimojo
- Department of Physics, Kumamoto University, Kumamoto 860-8555, Japan
| | - Rajiv K Kalia
- Collaboratory for Advanced Computing and Simulation, University of Southern California, Los Angeles, California 90089, United States
| | - Aiichiro Nakano
- Collaboratory for Advanced Computing and Simulation, University of Southern California, Los Angeles, California 90089, United States
| | - Priya Vashishta
- Collaboratory for Advanced Computing and Simulation, University of Southern California, Los Angeles, California 90089, United States
| | - Paulo S Branicio
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, United States
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5
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Jones RO. The chemical bond in solids-revisited. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:343001. [PMID: 35636399 DOI: 10.1088/1361-648x/ac7494] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2022] [Accepted: 05/30/2022] [Indexed: 06/15/2023]
Abstract
This article complements an earlier topical review of the chemical bond (Jones 2018J. Phys.: Condens. Matter30153001), starting in the mid-19th century and seen from the perspective of a condensed matter physicist. The discussion of applications focused on the structure and properties of phase change materials. We review here additional aspects of chemistry, particularly some that have raised interest recently in this context. Concepts such as 'electron-rich', 'electron-deficient (excess orbital)', 'hypervalent', 'three-centre', and 'metavalent' bonds, and 'multicentre hyperbonding' are now found in the condensed matter literature. They are surveyed here, as well as the bond in metals and the 'Peierls' distortion. What are these concepts, are they related, and are they sometimes new labels for established, but unfamiliar ideas? 'Half bonds' and 'fractional valencies' play a central role in this discussion. It is remarkable that they were introduced 100 years ago, but ignored or forgotten, and have needed to be rediscovered more than once.
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Affiliation(s)
- R O Jones
- Peter-Grünberg-Institut PGI-1 and JARA/HPC, Forschungszentrum Jülich, D-52425 Jülich, Germany
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6
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Rules of hierarchical melt and coordinate bond to design crystallization in doped phase change materials. Nat Commun 2021; 12:6473. [PMID: 34753920 PMCID: PMC8578292 DOI: 10.1038/s41467-021-26696-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2020] [Accepted: 09/27/2021] [Indexed: 11/23/2022] Open
Abstract
While alloy design has practically shown an efficient strategy to mediate two seemingly conflicted performances of writing speed and data retention in phase-change memory, the detailed kinetic pathway of alloy-tuned crystallization is still unclear. Here, we propose hierarchical melt and coordinate bond strategies to solve them, where the former stabilizes a medium-range crystal-like region and the latter provides a rule to stabilize amorphous. The Er0.52Sb2Te3 compound we designed achieves writing speed of 3.2 ns and ten-year data retention of 161 °C. We provide a direct atomic-level evidence that two neighbor Er atoms stabilize a medium-range crystal-like region, acting as a precursor to accelerate crystallization; meanwhile, the stabilized amorphous originates from the formation of coordinate bonds by sharing lone-pair electrons of chalcogenide atoms with the empty 5d orbitals of Er atoms. The two rules pave the way for the development of storage-class memory with comprehensive performance to achieve next technological node. In phase-change memory, writing speed and data retention are two seemingly conflicting performances. Here the authors report hierarchical melt and coordinate bond strategies to stabilize a medium-range crystal-like region and amorphous region, respectively.
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7
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Singh K, Kumari S, Singh H, Bala N, Singh P, Kumar A, Thakur A. A review on GeTe thin film-based phase-change materials. APPLIED NANOSCIENCE 2021. [DOI: 10.1007/s13204-021-01911-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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8
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Jia S, Li H, Gotoh T, Longeaud C, Zhang B, Lyu J, Lv S, Zhu M, Song Z, Liu Q, Robertson J, Liu M. Ultrahigh drive current and large selectivity in GeS selector. Nat Commun 2020; 11:4636. [PMID: 32934210 PMCID: PMC7493911 DOI: 10.1038/s41467-020-18382-z] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2020] [Accepted: 08/18/2020] [Indexed: 11/09/2022] Open
Abstract
Selector devices are indispensable components of large-scale nonvolatile memory and neuromorphic array systems. Besides the conventional silicon transistor, two-terminal ovonic threshold switching device with much higher scalability is currently the most industrially favored selector technology. However, current ovonic threshold switching devices rely heavily on intricate control of material stoichiometry and generally suffer from toxic and complex dopants. Here, we report on a selector with a large drive current density of 34 MA cm-2 and a ~106 high nonlinearity, realized in an environment-friendly and earth-abundant sulfide binary semiconductor, GeS. Both experiments and first-principles calculations reveal Ge pyramid-dominated network and high density of near-valence band trap states in amorphous GeS. The high-drive current capacity is associated with the strong Ge-S covalency and the high nonlinearity could arise from the synergy of the mid-gap traps assisted electronic transition and local Ge-Ge chain growth as well as locally enhanced bond alignment under high electric field.
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Affiliation(s)
- Shujing Jia
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-System and Information Technology, Chinese Academy of Sciences, Shanghai, 200050, China
- Key Laboratory of Microelectronic Devices and Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing, 100029, China
- University of Chinese Academy of Sciences, Beijing, 100029, China
| | - Huanglong Li
- Department of Precision Instrument, Tsinghua University, Beijing, 100084, China
- Chinese Institute for Brain Research, Beijing, 102206, China
| | - Tamihiro Gotoh
- Department of Physics, Graduate School of Science and Technology, Gunma University, Maebashi, 3718510, Japan
| | - Christophe Longeaud
- Group of Electrical Engineering of Paris, CNRS, Centrale Supelec, Paris Saclay and Sorbonne Universities, Plateau de Moulon, 91190, Gif sur Yvette, France
| | - Bin Zhang
- Analytical and Testing Center of Chongqing University, Chongqing, 401331, China
| | - Juan Lyu
- Department of Precision Instrument, Tsinghua University, Beijing, 100084, 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
| | - Min Zhu
- 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.
| | - Qi Liu
- Key Laboratory of Microelectronic Devices and Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing, 100029, China.
| | - John Robertson
- Engineering Department, University of Cambridge, Cambridge, CB3 0FA, UK
| | - Ming Liu
- Key Laboratory of Microelectronic Devices and Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing, 100029, China
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9
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Lee TH, Elliott SR. Chemical Bonding in Chalcogenides: The Concept of Multicenter Hyperbonding. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2020; 32:e2000340. [PMID: 32458525 DOI: 10.1002/adma.202000340] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2020] [Revised: 04/18/2020] [Accepted: 04/28/2020] [Indexed: 06/11/2023]
Abstract
The precise nature of chemical-bonding interactions in amorphous, and crystalline, chalcogenides is still unclear due to the complexity arising from the delocalization of bonding, and nonbonding, electrons. Although an increasing degree of electron delocalization for elements down a column of the periodic table is widely recognized, its influence on chemical-bonding interactions, and on consequent material properties, of chalcogenides has not previously been comprehensively understood from an atomistic point of view. Here, a chemical-bonding framework is provided for understanding the behavior of chalcogenides (and, in principle, other lone-pair materials) by studying prototypical telluride nonvolatile-memory, "phase-change" materials (PCMs), and related chalcogenide compounds, via density-functional-theory molecular-dynamics (DFT-MD) simulations. Identification of the presence of previously unconsidered multicenter "hyperbonding" (lone-pair-antibonding-orbital) interactions elucidates not only the origin of various material properties, and their contrast in magnitude between amorphous and crystalline phases, but also the very similar chemical-bonding nature between crystalline PCMs and one of the bonding subgroups (with the same bond length) found in amorphous PCMs, in marked contrast to existing viewpoints. The structure-property relationship established from this new bonding-interaction perspective will help in designing improved chalcogenide materials for diverse applications, based on a fundamental chemical-bonding point of view.
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Affiliation(s)
- Tae Hoon Lee
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
| | - Stephen R Elliott
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
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10
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Stellhorn JR, Hosokawa S, Kaiser B, Kimura K, Boudet N, Blanc N, Tajiri H, Kohara S, Pilgrim WC. The Structure of the Amorphous (GeTe)1–x
(Sb2Te3)
x
System and Implications for its Phase-Change Properties. ACTA ACUST UNITED AC 2020. [DOI: 10.1515/zpch-2020-1633] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
We describe structural features of ternary Ge-Sb-Te glasses based on anomalous X-ray scattering experiments for four different compositions along the pseudo-binary line (GeTe)1–x
(Sb2Te3)
x
for
0
≤
x
≤
2
3
$0\leq x\leq\frac{2}{3}$
, which comprises technologically important phase-change materials. The data are analyzed with reverse Monte Carlo modeling. This way, detailed information on the local environments around all constituent elements are obtained and their evolution with the chemical composition is described. This approach gives a consistent view of the atomic scale structure of the amorphous networks in these compounds. Thereby, it is possible to derive the relationship between the relevant material properties and the determining structural features. In particular, it is shown that the optical contrast related to the phase change is associated with the evolution of the Ge-Te core network.
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Affiliation(s)
- Jens R. Stellhorn
- Department of Physics , Kumamoto University , Kumamoto 860-8555 , Japan
- Department of Chemistry , Philipps University of Marburg , Marburg 35032 , Germany
- Present address: Department of Applied Chemistry , Hiroshima University , Hiroshima 739-8527 , Japan
| | - Shinya Hosokawa
- Department of Physics , Kumamoto University , Kumamoto 860-8555 , Japan
| | - Bernhard Kaiser
- Institute of Materials Science, Technical University of Darmstadt , Darmstadt 64287, Germany
| | - Koji Kimura
- Department of Physical Science and Engineering , Nagoya Institute of Technology , Nagoya 466-8555 , Japan
| | - Nathalie Boudet
- Institut Néel, University Grenoble Alpes and CNRS , Grenoble 38000 , France
| | - Nils Blanc
- Institut Néel, University Grenoble Alpes and CNRS , Grenoble 38000 , France
| | - Hiroo Tajiri
- Japan Synchrotron Radiation Research Institute (JASRI) , Hyogo 679-5198 , Japan
| | - Shinji Kohara
- Research Center for Advanced Measurement and Characterization, National Institute for Materials Science (NIMS) , Hyogo 679-5148 , Japan
- Center for Materials research by Information Integration (CMI ), Research and Services Division of Materials Data and Integrated System (MaDIS), National Institute for Materials Science (NIMS) , Ibaraki 305-0047 , Japan
- PRESTO, Japan Science and Technology Agency , Tokyo 102-0076, Japan
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11
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Yang WJ, Park H, Kim DS, Ha T, Park SJ, Ahn M, Kim JH, Kwon YK, Cho MH. Phase-change like process through bond switching in distorted and resonantly bonded crystal. Sci Rep 2019; 9:12816. [PMID: 31492917 PMCID: PMC6731313 DOI: 10.1038/s41598-019-49270-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2018] [Accepted: 08/07/2019] [Indexed: 11/08/2022] Open
Abstract
Although some methods to improve phase-change memory efficiency have been proposed, an effective experimental approach to induce a phase-change like process without external heat energy has not yet been reported. Herein we have shown that GeTe is a prototype phase-change material, which can exhibit a non-thermal phase-change-like process under uniaxial stress. Due to its structural characteristics like directional structural instability and resonance bonding under 1% uniaxial stress, we observed that bond switching in the GeTe film between short and long bonds is possible. Due to this phase change, GeTe displays the same phase-change as crystal layer rotation. Crystal layer rotation has not been observed in the conventional phase change process using intermediate states, but it is related to the structural characteristics required for maintaining local coordination. Moreover, since the resonance bonding characteristics are effectively turned off upon applying uniaxial stress, the high-frequency dielectric constant can be significantly decreased. Our results also show that the most significant process in the non-thermal phase transition of phase-change materials is the modulation of the lattice relaxation process after the initial perturbation, rather than the method inducing the perturbation itself. Finally, these consequences suggest that a new type of phase-change memory is possible through changes in the optical properties under stress.
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Affiliation(s)
- Won Jun Yang
- Department of Physics and Applied Physics, Yonsei University, Seoul, 03722, Republic of Korea
| | - Hanjin Park
- Department of Physics and Research Institute for Basic Sciences, Kyung Hee University, Seoul, 02447, Republic of Korea
| | - Da Sol Kim
- Department of Physics and Applied Physics, Yonsei University, Seoul, 03722, Republic of Korea
| | - Taewoo Ha
- Department of Physics and Applied Physics, Yonsei University, Seoul, 03722, Republic of Korea
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Sungkyunkwan University (SKKU), Suwon, 16419, Republic of Korea
| | - Seung Jong Park
- Department of Physics and Applied Physics, Yonsei University, Seoul, 03722, Republic of Korea
| | - Min Ahn
- Department of Physics and Applied Physics, Yonsei University, Seoul, 03722, Republic of Korea
| | - Jae Hoon Kim
- Department of Physics and Applied Physics, Yonsei University, Seoul, 03722, Republic of Korea
| | - Young-Kyun Kwon
- Department of Physics and Research Institute for Basic Sciences, Kyung Hee University, Seoul, 02447, Republic of Korea.
| | - Mann-Ho Cho
- Department of Physics and Applied Physics, Yonsei University, Seoul, 03722, Republic of Korea.
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12
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Wang G, Lotnyk A, Nie Q, Wang R, Shen X, Lu Y. Shortening Nucleation Time to Enable Ultrafast Phase Transition in Zn 1Sb 7Te 12 Pseudo-Binary Alloy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:15143-15149. [PMID: 30449104 DOI: 10.1021/acs.langmuir.8b02737] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Zn1Sb7Te12 thin films have been deposited by magnetron co-sputtering of ZnTe and Sb2Te3 targets. The microstructure, phase-change speed, optical cycling stability, and crystallization kinetics have been investigated during thermal annealing and laser irradiation. The thermal-annealed and laser-irradiated films give a clear evidence of the coexistence of trigonal Sb2Te3 and cubic ZnTe phases, which are homogeneously distributed in a single alloy as confirmed by advanced scanning transmission electron microscopy. The formation of both phases increases the initial nucleation sites, leading to the rapid phase-change speed in the Zn1Sb7Te12 film. The film has a minimum crystallization time of ∼3 ns at 70 mW with almost no incubation period for the formation of critical nuclei compared to Ge2Sb2Te5 and other Zn-based films. Moreover, the complete crystallization of Zn1Sb7Te12 thin films is achieved within 10 ns. The ultrafast two-dimensional nucleation and crystal growth speed in Zn1Sb7Te12 obtained from the laser-irradiated system is almost 7 times faster compared to that in Ge2Sb2Te5 film. Controlling the crystallization process through doping ZnTe into Sb2Te3 is thus promising for the development of high-speed optical switching technology.
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Affiliation(s)
- Guoxiang Wang
- Laboratory of Infrared Materials and Devices, The Research Institute of Advanced Technologies , Ningbo University , Ningbo , Zhejiang 315211 , China
- Leibniz Institute of Surface Engineering (IOM) , Permoserstr. 15 , D-04318 Leipzig , Germany
- Key Laboratory of Photoelectric Detection Materials and Devices of Zhejiang Province , Ningbo , Zhejiang 315211 , China
| | - Andriy Lotnyk
- Leibniz Institute of Surface Engineering (IOM) , Permoserstr. 15 , D-04318 Leipzig , Germany
| | - Qiuhua Nie
- Laboratory of Infrared Materials and Devices, The Research Institute of Advanced Technologies , Ningbo University , Ningbo , Zhejiang 315211 , China
- Key Laboratory of Photoelectric Detection Materials and Devices of Zhejiang Province , Ningbo , Zhejiang 315211 , China
| | - Rongping Wang
- Laboratory of Infrared Materials and Devices, The Research Institute of Advanced Technologies , Ningbo University , Ningbo , Zhejiang 315211 , China
- Key Laboratory of Photoelectric Detection Materials and Devices of Zhejiang Province , Ningbo , Zhejiang 315211 , China
| | - Xiang Shen
- Laboratory of Infrared Materials and Devices, The Research Institute of Advanced Technologies , Ningbo University , Ningbo , Zhejiang 315211 , China
- Key Laboratory of Photoelectric Detection Materials and Devices of Zhejiang Province , Ningbo , Zhejiang 315211 , China
| | - Yegang Lu
- Laboratory of Infrared Materials and Devices, The Research Institute of Advanced Technologies , Ningbo University , Ningbo , Zhejiang 315211 , China
- Key Laboratory of Photoelectric Detection Materials and Devices of Zhejiang Province , Ningbo , Zhejiang 315211 , China
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13
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Cao X, Meng C, Li J, Wang J, Yuan Y, Su J, Liu C, Zhang X, Zhang H, Wang J. Characterization of interfacial barrier charging as a resistive switching mechanism in Ag/Sb 2Te 3/Ag heterojunctions. Phys Chem Chem Phys 2018; 20:18200-18206. [PMID: 29796567 DOI: 10.1039/c8cp00901e] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In this study, bipolar memristive behaviors were systematically characterized in Ag/Sb2Te3/Ag hetero-junctions. By using in situ Raman and photoluminescence spectroscopy, a direct observation of the bonding environment and band structure confirmed that resistive switches are strongly related to the electronic valence changes in Sb2Te3 and the formation of Schottky barriers at Ag/Sb2Te3 interfaces. Band movement of Sb2Te3 acquired by first-principles calculations also supports the electrostatic barrier charging as a memristive mechanism of Ag/Sb2Te3/Ag heterocells. Independent resistance-switching behaviors that can be utilized in both amorphous and crystalline Sb2Te3 lead to multiple resistance values with a large memory window (104-105) and low read voltage (∼0.2 V), giving rise to a unique multi-level memory concept. This study based on Ag/Sb2Te3/Ag hetero-junctions offers a significant understanding to promote the use of Sb2Te3 and other chalcogenide memristors as promising candidates for compatible high-density memory applications.
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Affiliation(s)
- Xinran Cao
- Shanghai Ultra-Precision Optical Manufacturing Engineering Center, Department of Optical Science and Engineering, Fudan University, Shanghai, 200433, China.
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14
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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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15
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Mantovan R, Fallica R, Mokhles Gerami A, Mølholt TE, Wiemer C, Longo M, Gunnlaugsson HP, Johnston K, Masenda H, Naidoo D, Ncube M, Bharuth-Ram K, Fanciulli M, Gislason HP, Langouche G, Ólafsson S, Weyer G. Atomic-scale study of the amorphous-to-crystalline phase transition mechanism in GeTe thin films. Sci Rep 2017; 7:8234. [PMID: 28811632 PMCID: PMC5558007 DOI: 10.1038/s41598-017-08275-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2017] [Accepted: 07/10/2017] [Indexed: 11/25/2022] Open
Abstract
The underlying mechanism driving the structural amorphous-to-crystalline transition in Group VI chalcogenides is still a matter of debate even in the simplest GeTe system. We exploit the extreme sensitivity of 57Fe emission Mössbauer spectroscopy, following dilute implantation of 57Mn (T½ = 1.5 min) at ISOLDE/CERN, to study the electronic charge distribution in the immediate vicinity of the 57Fe probe substituting Ge (FeGe), and to interrogate the local environment of FeGe over the amorphous-crystalline phase transition in GeTe thin films. Our results show that the local structure of as-sputtered amorphous GeTe is a combination of tetrahedral and defect-octahedral sites. The main effect of the crystallization is the conversion from tetrahedral to defect-free octahedral sites. We discover that only the tetrahedral fraction in amorphous GeTe participates to the change of the FeGe-Te chemical bonds, with a net electronic charge density transfer of ~ 1.6 e/a0 between FeGe and neighboring Te atoms. This charge transfer accounts for a lowering of the covalent character during crystallization. The results are corroborated by theoretical calculations within the framework of density functional theory. The observed atomic-scale chemical-structural changes are directly connected to the macroscopic phase transition and resistivity switch of GeTe thin films.
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Affiliation(s)
- R Mantovan
- Laboratorio MDM, IMM-CNR, Via Olivetti 2, 20864, Agrate Brianza (MB), Italy.
| | - R Fallica
- Laboratorio MDM, IMM-CNR, Via Olivetti 2, 20864, Agrate Brianza (MB), Italy.,Laboratory for Micro- and Nanotechnology, Paul Scherrer Institute, 5232, Villigen PSI, Switzerland
| | - A Mokhles Gerami
- Physics Department, ISOLDE/CERN, Geneva 23, Switzerland.,Dept. of Physics, K. N. Toosi University of Technology, P.O. Box 15875-4416, Tehran, Iran
| | - T E Mølholt
- Physics Department, ISOLDE/CERN, Geneva 23, Switzerland
| | - C Wiemer
- Laboratorio MDM, IMM-CNR, Via Olivetti 2, 20864, Agrate Brianza (MB), Italy
| | - M Longo
- Laboratorio MDM, IMM-CNR, Via Olivetti 2, 20864, Agrate Brianza (MB), Italy.
| | - H P Gunnlaugsson
- Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavík, Iceland
| | - K Johnston
- Physics Department, ISOLDE/CERN, Geneva 23, Switzerland
| | - H Masenda
- School of Physics, University of the Witwatersrand, Johannesburg, 2050, South Africa
| | - D Naidoo
- School of Physics, University of the Witwatersrand, Johannesburg, 2050, South Africa
| | - M Ncube
- School of Physics, University of the Witwatersrand, Johannesburg, 2050, South Africa
| | - K Bharuth-Ram
- Durban University of Technology, Durban, 4000, South Africa.,School of Chemistry and Physics, University of KwaZulu-Natal, Durban, 4000, South Africa
| | - M Fanciulli
- Laboratorio MDM, IMM-CNR, Via Olivetti 2, 20864, Agrate Brianza (MB), Italy.,Dipartimento di Scienza dei Materiali, Università di Milano Bicocca, Milano, Italy
| | - H P Gislason
- Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavík, Iceland
| | - G Langouche
- KU Leuven, Instituut voor Kern-en Stralings Fysika, B-3001, Leuven, Belgium
| | - S Ólafsson
- Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavík, Iceland
| | - G Weyer
- Department of Physics and Astronomy, Aarhus University, Aarhus C, Denmark
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16
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Velea A, Opsomer K, Devulder W, Dumortier J, Fan J, Detavernier C, Jurczak M, Govoreanu B. Te-based chalcogenide materials for selector applications. Sci Rep 2017; 7:8103. [PMID: 28808294 PMCID: PMC5556072 DOI: 10.1038/s41598-017-08251-z] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2017] [Accepted: 07/10/2017] [Indexed: 11/18/2022] Open
Abstract
The implementation of dense, one-selector one-resistor (1S1R), resistive switching memory arrays, can be achieved with an appropriate selector for correct information storage and retrieval. Ovonic threshold switches (OTS) based on chalcogenide materials are a strong candidate, but their low thermal stability is one of the key factors that prevents rapid adoption by emerging resistive switching memory technologies. A previously developed map for phase change materials is expanded and improved for OTS materials. Selected materials from different areas of the map, belonging to binary Ge-Te and Si-Te systems, are explored. Several routes, including Si doping and reduction of Te amount, are used to increase the crystallization temperature. Selector devices, with areas as small as 55 × 55 nm2, were electrically assessed. Sub-threshold conduction models, based on Poole-Frenkel conduction mechanism, are applied to fresh samples in order to extract as-processed material parameters, such as trap height and density of defects, tailoring of which could be an important element for designing a suitable OTS material. Finally, a glass transition temperature estimation model is applied to Te-based materials in order to predict materials that might have the required thermal stability. A lower average number of p-electrons is correlated with a good thermal stability.
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Affiliation(s)
- A Velea
- Imec, Kapeldreef 75, 3001, Heverlee, Belgium.
- National Institute of Materials Physics, Atomistilor 405A, P.O. Box M.G. 7, Magurele, 077125, Ilfov, Romania.
| | - K Opsomer
- Imec, Kapeldreef 75, 3001, Heverlee, Belgium
| | - W Devulder
- Imec, Kapeldreef 75, 3001, Heverlee, Belgium
| | - J Dumortier
- Ghent University, dept. Solid State Sciences, Krijgslaan 281 (S1), 9000, Ghent, Belgium
| | - J Fan
- Imec, Kapeldreef 75, 3001, Heverlee, Belgium
| | - C Detavernier
- Ghent University, dept. Solid State Sciences, Krijgslaan 281 (S1), 9000, Ghent, Belgium
| | - M Jurczak
- Imec, Kapeldreef 75, 3001, Heverlee, Belgium
| | - B Govoreanu
- Imec, Kapeldreef 75, 3001, Heverlee, Belgium
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17
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Lee TH, Elliott SR. The Relation between Chemical Bonding and Ultrafast Crystal Growth. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2017; 29. [PMID: 28417576 DOI: 10.1002/adma.201700814] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2017] [Revised: 03/07/2017] [Indexed: 05/09/2023]
Abstract
Glasses are often described as supercooled liquids, whose structures are topologically disordered like a liquid, but nevertheless retain short-range structural order. Structural complexity is often associated with complicated electron-charge distributions in glassy systems, making a detailed investigation challenging even for short-range structural order, let alone their atomic dynamics. This is particularly problematic for lone-pair-rich, semiconducting materials, such as phase-change materials (PCMs). Here, this study shows that analytical methods for studying bonding, based on the electron-charge density, rather than a conventional atomic pair-correlation-function approach, allows an in-depth investigation into the chemical-bonding network, as well as lone pairs, of the prototypical PCM, Ge2 Sb2 Te5 (GST). It is demonstrated that the structurally flexible building units of the amorphous GST network, intimately linked to the presence of distinctly coexisting weak covalent and lone-pair interactions, give rise to cooperative structural-ordering processes, by which ultrafast crystal growth becomes possible. This finding may universally apply to other PCMs.
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Affiliation(s)
- Tae Hoon Lee
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
| | - Stephen R Elliott
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
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18
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Guo S, Xu L, Zhang J, Hu Z, Li T, Wu L, Song Z, Chu J. Enhanced Crystallization Behaviors of Silicon-Doped Sb2Te Films: Optical Evidences. Sci Rep 2016; 6:33639. [PMID: 27640336 PMCID: PMC5027526 DOI: 10.1038/srep33639] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2016] [Accepted: 08/31/2016] [Indexed: 11/09/2022] Open
Abstract
The optical properties and structural variations of silicon (Si) doped Sb2Te (SST) films as functions of temperature (210–620 K) and Si concentration (0–33%) have been investigated by the means of temperature dependent Raman scattering and spectroscopic ellipsometry experiments. Based upon the changes in Raman phonon modes and dielectric functions, it can be concluded that the temperature ranges for intermediates and transition states are estimated to 150, 120, 90, and 0 K, corresponding to ST, SST25%, SST28%, and SST33% films, respectively. The phenomenon also can be summarized by the thermal evolutions of interband electronic transition energies (En) and partial spectral weight integral (I). The disappearance of intermediate (INT) state for SST33% film between amorphous (AM) and hexagonal (HEX) phases can be attributed to the acceleratory crystallization of HEX phase by Si introduction. It illustrates that the risk of phase separation (Sb and Te) during the cyclic phase-change processes decreases with the increasing Si concentration. The enhanced crystallization behaviors can optimize the data retention ability and the long term stability of ST by Si doping, which are important indicators for phase change materials. The performance improvement has been analyzed qualitatively from the optical perspective.
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Affiliation(s)
- Shuang Guo
- Department of Electronic Engineering, East China Normal University, Shanghai 200241, China
| | - Liping Xu
- Department of Electronic Engineering, East China Normal University, Shanghai 200241, China
| | - Jinzhong Zhang
- Department of Electronic Engineering, East China Normal University, Shanghai 200241, China
| | - Zhigao Hu
- Department of Electronic Engineering, East China Normal University, Shanghai 200241, China
| | - Tao Li
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Liangcai Wu
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Zhitang Song
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Junhao Chu
- Department of Electronic Engineering, East China Normal University, Shanghai 200241, China
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19
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Kaes M, Salinga M. Impact of defect occupation on conduction in amorphous Ge2Sb2Te5. Sci Rep 2016; 6:31699. [PMID: 27526783 PMCID: PMC4985640 DOI: 10.1038/srep31699] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2016] [Accepted: 07/27/2016] [Indexed: 11/08/2022] Open
Abstract
Storage concepts employing the resistance of phase-change memory (PRAM) have matured in recent years. Attempts to model the conduction in the amorphous state of phase-change materials dominating the resistance of PRAM devices commonly invoke a connection to the electronic density-of-states (DoS) of the active material in form of a "distance between trap states s". Here, we point out that s depends on the occupation of defects and hence on temperature. To verify this, we numerically study how the occupation in the DoS of Ge2Sb2Te5 is affected by changes of temperature and illumination. Employing a charge-transport model based on the Poole-Frenkel effect, we correlate these changes to the field- and temperature-dependent current-voltage characteristics of lateral devices of amorphous Ge2Sb2Te5, measured in darkness and under illumination. In agreement with our calculations, we find a pronounced temperature-dependence of s. As the device-current depends exponentially on the value of s, accounting for its temperature-dependence has profound impact on device modeling.
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Affiliation(s)
- Matthias Kaes
- I.Physikalisches Institut (IA), RWTH Aachen University, Sommerfeldstrasse 14, 52074 Aachen, Germany
| | - Martin Salinga
- I.Physikalisches Institut (IA), RWTH Aachen University, Sommerfeldstrasse 14, 52074 Aachen, Germany
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