Phys. for Phase-Change Memory Zhen Li, y Chen Si, y Jian Zhou, , y Huibin Xu, y , z and Zhimei Sun , y , z y School of Materials Science and Engineering, Beihang University, Beijing 100191, China This structure can be viewed as a rock-salt structure slightly distorted along the ⟨ 111 ⟩  direction with a subsequent shear relaxation. Their ability to switch, reversibly and extremely quickly, between the crystalline and amorphous phases, combined with the high stability of both phases, makes them ideally suitable for … 2016. Schematic of the formation of a vacancy and twofold coordinated Te atoms as a result of Sb substitution in GeTe [46.59]. The proposal that the bonding in the crystalline state of GST is resonant while in the amorphous state it is purely covalent [46.23, 46.24, 46.25] implicitly suggested that the underlying mechanism of the phase transition consisted of the establishment – or destruction – of resonance bonding between the covalently bonded fragments. Math. T. Matsunaga, R. Kojima, N. Yamada, K. Kifune, Y. Kubota, M. Takata: Appl. In addition, interesting magnetic responses from iPCM were observed [46.76, 46.77] that were not present in composite material of the same average composition, making iPCM-based structures promising for spintronic and topotronic applications. Kang, J. Lee, Y. Kwon, S. Kim, J. Kim, Y.-J. } and (b) Evolution of CDD clouds during the in-silico amorphization process using DFT simulations substantiating the schematic shown in the upper panel. Phase-change materials are Te-containing alloys, typically lying along the GeTe-Sb2Te3 quasibinary tie line. Subsequent electron diffraction studies [46.31, 46.32] obtained similar radial distribution functions. Rep. (2015), doi: A.V. Sharma, J.P. de NeufvilleL: J. Non-Cryst. Feature Flags: { Reprinted with permission). Kolobov, J. Tominaga, N. Yamada: Appl. Comparison of optics, recording densities, recording capacities and disk structures used for CD, DVD, and BD. A similar approach was used to explain the existence of Ge(3):Te(3) configurations in [46.58], where the authors also considered the formation of Ge-Te bonds that involved the lone-pair electrons of Te. © 2020 Springer Nature Switzerland AG. A major development in energy efficiency was realized by the spatial separation of GeTe and Sb2Te3 into atomically thin layers. About 60% of Ge atoms were found to be fourfold coordinated but only 34% were tetrahedrally bonded. Raman scattering and far-infrared absorption spectra for a-GeTe [46.36] were equally interpreted in terms of the presence of GeTe4 tetrahedra. What makes the GeTe alloys special? [46.48] were the first to apply ab-initio simulations based on density functional theory for phase-change materials, using the spinel structure (in which Ge atoms are tetrahedrally coordinated) to model the amorphous phase. Mu, Jianwei A fragment of the amorphous structure showing an ABAB cube [46.51]. Nash, Geoffrey R. S.J. Lam, Chung Recent years have witnessed significant progress in the understanding of the atomistic mechanism of phase change. A.V. While it is generally believed that the role of light in the phase-change process is to heat the material above the melting point – which is likely to be correct for longer pulses – exposure to shorter pulses is different. Sui, Yongxing The structure of Ge2Sb2Te5 was described as a layered structure with the stacking sequence along the c-axis of Te-Sb-Te-Ge-Te-Te-Ge-Te-Sb-Te. If, on the other hand, the melt is cooled fast enough so that the structure cannot follow the change in temperature, the disordered phase is frozen; one obtains a supercooled liquid and subsequently a glass. Kolobov et al. Amorphous Ge2Sb2Te5 has subsequently been studied using EXAFS by other groups [46.42, 46.43, 46.44] and similar results were obtained although in addition the presence of Ge-Ge bonds was also reported. Corresponding Author. Li, Xun Solids. The change in beam cross-section is displayed at the bottom. Analysis of electron-diffraction results led the authors to conclude that the studied crystals possessed a hexagonal cell with space group $$P\overline{3}m1$$ and the lattice constants $$a={\mathrm{4.20}}\pm{\mathrm{0.02}}$$ and $$c={\mathrm{16.96}}\pm{\mathrm{0.06}}\,{\mathrm{\AA}}$$ and $$a={\mathrm{4.21}}\pm{\mathrm{0.02}}$$ and $$c={\mathrm{23.65}}\pm{\mathrm{0.08}}\,{\mathrm{\AA}}$$ for Ge2Sb2Te5 and GeSb4Te7, respectively. and Reprinted with permission), (a) Schematic of the formation of a tetrahedral Ge configuration. The electrical current passes through the phase change material between the top electrode and heater. They have been long used in optical data storage in the form of DVD and Blu-Ray disks and recently have also emerged as a leading candidate for electronic nonvolatile memory devices. Phase change materials store information in their amorphous and crystalline phases, which can be reversibly switched by the application of an external voltage. This alignment is lost in the amorphous phase and this has a drastic effect on materials’s properties such as optical contrast and resistivity [46.26]. You, S.R. For the amorphous phase, it was found that Ge-Te and Sb-Te bonds become shorter and the structure possessed more local order than the crystalline phase as evidenced by the more intense and narrower peaks in the spectra corresponding to the amorphous phase (Fig. Kolobov, P. Fons, J. Tominaga: Phys. (Reprinted from [46.20] by permission from Macmillan Publishers Ltd, copyright (2004)). and Saltzmann, Tobias The physical properties of phase change materials that enable data storage are described, and our current knowledge of the phase change processes is summarized. P. Boolchand, B.B. A very simplified picture of the phase-change process is based on the idea that as the temperature of the melt decreases, the viscosity becomes larger, and at a certain point the structure can no longer follow the change in temperature. Lett. Phase-change random access memory (PRAM) is a new form of nonvolatile memory based on using electrical charges to change areas on a glassy material from crystalline to random. Silva, Helena Ovshinksky was the first person to discuss the cognitive computing and neural networks in the context of phase change materials [46.81]. Hosseini, Peiman Hewlett-Packard's micro-mover technology can accurately position the platter to 3 nm so densities of more than 1 Tbit (125 GB) per square inch will be possible if the technology can … Phase change materials store information in their amorphous and crystalline phases, which can be reversibly switched by the application of an external voltage. Richardson Jr., J.-H. Chung, T. Egami: Appl. Aswal, D K The animation was presented in IEDM 2006 to show how phase change memory (PCM) devices switch between its amorphous and crystalline states. A shape-memory alloy is an alloy that can be deformed when cold but returns to its pre-deformed ("remembered") shape when heated. Rev. Song, Zhitang Rev. Hjalmarson, C.J. Mater. In particular, it exhibits very good endurance on the order of 1 million cycles or more, moderate retention, and superb scalability to sub-20-nm nodes and beyond. Kolobov: Appl. Cite as. The Ge-Te bond length (2.59 Å) was also found to be consistent with the 4(Ge):2(Te) bonding geometry [46.35]. Phase Change Symp. Taguchi, N. Yamada, T. Proffen: Jpn. Phase change materials have a large electrical contrast; for Fig. Phase change memory materials store information through their reversible transitions between crystalline and amorphous states. The 4(Ge):2(Te)-coordinated structure was also suggested on the basis of EXAFS measurements around both Ge and Te K-edges [46.33, 46.34, 46.35]. pp 1-1 | Peacock: Thin Solid Films. Zhang, Jianhao Finally, potential new applications of phase change devices such as neuromorphic computing and phase change logic are outlined. A. Kolobov, P. Fons, A. Frenkel, A. Ankudinov, J. Tominaga, T. Uruga: Nat. Silva, Helena PCM is considered an emerging technology. – Phase Change Nonmagnetic Mater. Bhaskaran, Harish Rev. Phase change materials (PCMs) are substances which absorb or release large amounts of so-called “latent” heat when they go through a change in their physical state, i.e., from solid to liquid and vice versa. Abstract Ge-Sb-Te (GST)-based phase-change memory (PCM) excels in the switching performance but remains insufficient of the operating speed to replace cache memory (the fastest memory in a computer). Their results are described as follows in more detail. Shindo, S. Nanotech. Kolobov, P. Fons, J. Tominaga, S.R. In early work, it was tacitly assumed that upon exposure of the crystalline phase to an intense laser or current pulse, phase-change materials melt and are subsequently quenched into a (completely) disordered amorphous state. And challenges of PCM are addressed, and Polyester GeTe-based alloys have commercial... Distinguish you from other users and to provide an atomistic description of the amorphous.... Using Sb2Te3 templates is proposed to boost the crystallization speed of GST by five faster... Energy of the presence phase change memory materials bonds with Ge or Sb favors a tetrahedral Ge configuration 46.22 ] memory cycling -! Of defective octahedral Ge sites in the as-deposited amorphous phase temperature and the point. M. Krbal, T. Proffen, J.W by Betts et al new memory types, phase-change memory was invented the! 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