Solids. From CD to DVD and DVD to BD, the effective laser beam cross section has been reduced by a factor of 2 and 5, respectively. and } In both, data storage is effected by fast, reversible phase changes between crystalline and amorphous states. The observed bond shortening and increased local order are highly unusual for covalent solids when, due to anharmonicity of the interatomic potential, disorder usually results in longer and weaker bonds and suggests that the local structures in the two cases are significantly different. Bond shortening in the as-deposited amorphous phase of Ge2Sb2Te5 has also been observed by high-energy x-ray scattering experiments [46.45]. "openAccess": "0", I. Petrov, R. Imamov, Z. Pinsker: Sov. Jung, K.J. Rev. Guo, Tianqi Recent years have witnessed significant progress in the understanding of the atomistic mechanism of phase change. What makes the GeTe alloys special? A. Kolobov, P. Fons, M. Krbal, R. Simpson, S. Hosokawa, T. Uruga, H. Tanida, J. Tominaga: Appl. 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. The Scaling of Phase-Change Memory Materials and Devices. The identification of materials suitable for non-volatile phase-change memory applications is driven by the need to find materials with tailored properties for different technological applications and the desire to understand the scientific basis for their unique properties. Mater. Chem. J.-P. Gaspard, A. Pellegatti, F. Marinelli, C. Bichara: Philos. Lett. A gradual upwards drift in the electrical resistance of Ge-Sb-Te alloys has been observed after switching to the amorphous state that potentially can cause problems for multilevel storage applications in PRAM. PCM is considered to be a storage class memory in which unlike flash its elements are individually addressable, have a demonstrated cyclability of over 1011 cycles, and have access times on the tens to hundreds of nanoseconds scale. It should also be noted that despite the bond shortening, the density of the amorphous phase is about 5% lower than that of the crystalline phase. Saito, Y. CONFERENCE PROCEEDINGS Papers Presentations Bhaskaran, Harish However, such a technology can succeed only if it can scale smaller in size, given the increasingly tiny memory cells that are projected for future technology nodes (i.e., generations). Li, Le Bhaskaran, Harish The liquid structure (270 atom) generated at 2300 K was equilibrated for 6 ps and then quenched in 16 ps and further equilibrated for 18 ps at 990 K. In order to generate a model of a-Ge2Sb2Te5, the liquid was then brought to 300 K in 18 ps. Zou, Hua From these studies it was concluded that electronic excitation considerably lowers the critical amorphization temperature and reduces the atomic diffusion coefficient with respect to that of the corresponding liquid phase by at least one order of magnitude. B, P. Fons, H. Osawa, A.V. S. Gabardi, S. Caravati, G.C. Kuramochi, Eiichi and In the device-relevant phase-change process, a short intense laser or current pulse melts the material that is subsequently quenched into the amorphous phase. [46.80], the concept of neural networks came into vogue. "subject": true, Download PDF Abstract: We survey the current state of phase change memory (PCM), a non-volatile solid-state memory technology built around the large electrical contrast between the highly-resistive amorphous and highly-conductive crystalline states in so-called phase change materials. It should be noted that in this work laser-crystallized and laser-amorphized states of GST were studied, that is, exactly the structures that are used in optical memory devices (the measurements were performed on real-device structures). S. Caravati, M. Bernasconi, T.D. T. Matsunaga, H. Morita, R. Kojima, N. Yamada, K. Kifune, Y. Kubota, Y. Tabata, J.-J. Shindo, S. O. Uemura, Y. Sagara, M. Tsushima, T. Kamikawa, T. Satoh: J. Non-Cryst. S. Caravati, M. Bernasconi, T. Kühne, M. Krack, M. Parrinello: Appl. Feature Flags: { The phase-change material, Ge 2 Sb 2 Te 5, is the canonical material ingredient for next-generation storage-class memory devices used in novel computing architectures, but fundamental questions remain regarding its atomic structure and physicochemical properties. (2001). Song, Y.-H. and Kolomiets, E.A. Gokirmak, Ali Using phase change memory bridge devices of variable length, we prove unambiguously that the important parameter for threshold switching is a critical electrical field and not a threshold voltage. The Science Behind PCM’s. Hayat, Hasan Outlast phase change materials can be found permanently enclosed in fibers, which are spun into yarn and then used to make thermo-regulating mattresses, sheets, and other bedding items. "metrics": true, Current crowding at the ‘‘heater’’ to phase change material contact results in … The study found square fragments dominated the structure of a GST. 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 memory … E‐mail: xilin_zhou@sutd.edu.sg, robert_simpson@sutd.edu.sg Search for more papers by this author. Two CDD slice – separated by a black dashed line – one for each of the two 3c–4e bonds, are shown on the right. Hayat, Hasan (et al.) Electron. Sosso, J. Behler, M. Bernasconi: Phys. (Reprinted from [46.20] by permission from Macmillan Publishers Ltd, copyright (2004)). Chalcogenide phase-change materials (PCMs) are currently at the forefront of this endeavor. Song, Sannian With the commercial realization of phase-change memory, the field of phase-change materials is primed for further progress. The fundamental mechanism for Phase-Change Memory was invented in the 1960s by Stanford Robert Ovshinsky. 2015. 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. […] after switching from a highly resistive state, structural changes result in the preservation of a conductive state even when the current is totally removed. Cryan, Martin J. Nakamura: Sci. Zhang: Phys. Copyright © Materials Research Society 2014, Hostname: page-component-546c57c664-xrkbf X. Yu, J. Robertson: Sci. and Phys. The electronic excitation was modeled by removing electrons from the high lying valence band states according to the strength of the excitation, where the authors used a jellium background charge to compensate for the loss of charged carriers. Mater. Kolobov, T. Fukaya, M. Krbal, T. Yagi, J. Tominaga: Nat. The electrical and thermal proper- ties of phase change materials are surveyed witha focus on the scalability of the materials and their impact on device design. Not affiliated Phys. The photo-induced amorphization of Ge2Sb2Te5 upon exposure to 600 ps pulses was first studied using in-situ x-ray absorption spectroscopy [46.62]. The rock-salt like arrangement of atoms in the crystalline phase requires the formation of six bonds by each participating atom while at the same time, the number of valence electrons located on Ge and Sb atoms is lower. T. Matsunaga, N. Yamada, Y. Kubota: Acta Cryst. In this Review, we focus on the mechanisms of the spontaneous structural relaxation – aging – of amorphous PCMs, which causes the well-known resistance drift issue that significantly reduces the device accuracy needed for phase-change memory and computing applications. Going from DVD to the dual-layer BD another increase by a factor of 11 has been accomplished. Lett. Sui, Yongxing Lett. Rep. (2015), doi: A.V. PCM has been successfully used in optical memory devices such as DVD-RAM since the 1990s and recently commercial production of electronic nonvolatile phase-change random access memory (PRAM ) has been launched by two of the world’s leading memory makers Samsung and Micron. Solids, M. Paesler, D. Baker, G. Lucovsky, A. Edwards, P. Taylor: J. Phys. The local structure around the Ge species is very similar to that of the binary GeTe, which possesses a rhombohedral structure with subsets of three shorter and three longer bonds. Ríos, Carlos B, T. Chattopadhyay, J. Boucherle, H. Von Schnering: J. Phys. "crossMark": true, Rev. Various designs of PCM devices with their respective advantages and integration challenges are presented. carbon nanotube memory 8, 9), or in the resistance of the storage media itself (phase change RAM 10). [46.20] were the first to go beyond simple measurements and proposed structural models. * Views captured on Cambridge Core between September 2016 - 1st January 2021. Even though flash memory represents today the leading technology, to allow its scalability down to the 16 nm technology node and beyond, new architectures are necessary. (c) Zooms into vicinities of the atoms that participate in the formation of three-center bonds. Richardson Jr., J.-H. Chung, T. Egami: Appl. Welnic et al. Data are stored not as charge but as a physical structural difference in the … As a result, two Sb atoms (shown in magenta in Fig. Phys. 2015. X-ray diffraction structural studies made by Betts et al. 2014. Lam, Chung A natural PCM is water/ice. Data Storage (2003). Problems with conventional submicron lithography and flexible substrates were avoided by using a Si-based block co-polymer for patterning in lieu of conventional optical lithography [46.78]. Combined photoemission and inverse photoemission studies [46.37] also favored the 4(Ge):2(Te) coordination. Wright, C. David Scherer, Torsten and This sequence is sometimes referred to as the Petrov sequence. and Pellizzer, Fabio. Ge atoms are shown in green and Te atoms are shown in orange. The cycling endurance of phase-change memory is one of the last hurdles to overcome to enable its adoption in the larger market for persistent memory products. Phase change materials have a large electrical contrast; for Fig. Phys. Comparison of optics, recording densities, recording capacities and disk structures used for CD, DVD, and BD. Raman scattering and far-infrared absorption spectra for a-GeTe [46.36] were equally interpreted in terms of the presence of GeTe4 tetrahedra. Pennycook, Stephen J. An example of Ge2Sb2Te5 based synapses exhibiting the spike-timing-dependent plasticity required for neuromorphic computing was reported in 2012 [46.82]. Jurado, Zoila Dronskowski, Richard The material can be reversibly switched back to the highly resistive state by application of a current pulse of either polarity exceeding a threshold value. When the temperature dips down to … In this chapter, a detailed description of these materials is provided starting with the global and local structures of the two phases, which were extensively studied both experimentally and using ab initio computer simulations, and followed by the discussion of possible atomistic mechanisms of the phase-change process, with special accent on the role of electronic excitation. ACTA Lab, Singapore University of Technology and Design, 8 Somapah Road, 487372 Singapore. 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]. It may also be called memory metal, memory alloy, smart metal, smart alloy, or muscle wire. The role of electronic excitation in the phase-change process was also investigated theoretically [46.64]. Subsequently these studies were extended [46.50]. It is interesting to note that the obtained values of the fraction of Ge-Ge bonds were similar to the concentration of tetrahedral Ge sites, suggesting a correlation between the two. Campi, Davide 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. Phase change RAM (PCRAM) and resistive RAM are somewhat simpler to construct than MRAM. T. Matsunaga, R. Kojima, N. Yamada, K. Kifune, Y. Kubota, M. Takata: Appl. 2015. At the same time, the bonding localized along the longer bonds is significantly lower clear demonstrating a pronounced bonding energy difference between the short and long bonds. The P-RAM uses the fact that the chalcogenide glass changes between two states, polycrystalline and amorphous by the passage of current which produces heat as it passes through a cell. Phase-change alloys are a class of important materials for data-storage applications. Wei, Shuai This work, however, only reported the obtained numerical values and stayed short of drawing further conclusions. Vacancies were also argued to account for the p-type conductivity of the crystalline phase of GeTe [46.29]. Solid-State Circuits Conf. Here, we report the obse … B, T. Nonaka, G. Ohbayashi, Y. Toriumi, Y. Mori, H. Hashimoto: Thin Solid Films. Sullivan, Lindsay More recently, a large-scale 165000 synapse neural network based upon phase-change materials was fabricated and in a prototypical use applied to the recognition of handwriting [46.83]. Cond. Yuhan Chen, Liang Sun, Yuxing Zhou, Getasew M. Zewdie, Volker L. Deringer, Riccardo Mazzarello, Wei Zhang, Chemical understanding of resistance drift suppression in Ge–Sn–Te phase-change memory materials, Journal of Materials Chemistry C, 10.1039/C9TC04810C, (2019). Solids. Data Storage Mater. Charact. [citation needed]Parts made of shape-memory alloys can be lightweight, solid-state alternatives to conventional actuators such as hydraulic, pneumatic, and motor-based … B, P. Jovari, I. Kaban, J. Steiner, B. Beuneu, A. Schops, M.A. The chapter is concluded by a brief description of the present and emerging applications of this class of chalcogenide materials. In this work, a novel approach using Sb2Te3 templates is proposed to boost the crystallization speed of GST by five times faster. Reprinted with permission), (a) Schematic of the formation of a tetrahedral Ge configuration. Koike, J. The stable phase of Ge2Sb2Te5 was subsequently re-examined by Kooi et al. If you should have access and can't see this content please, Ferroelectric Random Access Memories: Fundamentals and Applications, Phase Change Materials: Science and Application. J. Tominaga, A.V. K. Shportko, S. Kremers, M. Woda, D. Lencer, J. Robertson, M. Wuttig: Nat. Rep. M. Hada, W. Oba, M. Kuwahara, I. Katayama, T. Saiki, J. Takeda, K.G. Longo, Massimo Phase change materials store information in their amorphous and crystalline phases, which can be reversibly switched by the application of an external voltage. As a consequence, this kind of memory materials was named interfacial phase-change memory (iPCM ). 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. J. Appl. B. T. Matsunaga, P. Fons, A.V. Wang, Di Part of Springer Nature. Nowak, Rebecca Although the ideas behind neuron-based computing date back to the 1940s with the advent the theory of threshold computing [46.79], the development of electrical devices capable of carrying out such operations in a physical system came much later. Feng, Songlin Han, H.-B. The distortion of the Ge atom location was subsequently confirmed experimentally using scattering measurements [46.21, 46.22]. Carrillo, Santiago García-Cuevas Nanotech. Kolobov, P. Fons, J. Tominaga: Sci. Starting with the liquid phase, they found the existence of four-membered rings (4-rings), analogous to the ABAB blocks of [46.51], even at temperatures as high as 1073 K. They found that the concentration of 4-rings increased as the temperature decreased and this increase was found to be correlated with the size of the maximal cluster of connected square rings. Lett. Rev. These authors performed EXAFS studies on as-deposited and thermally crystallized layers of GeTe and GST and obtained the bond lengths characteristic of the two states. Mitrofanov, A.V. ST holds a license to the patents that resulted from that original development and has built onto that ground-breaking work for more than 15 years, developing the embedded PCM solution (ePCM) that is today integrated into our 28nm FD-SOI technology platform. "metricsAbstractViews": false, 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. Query parameters: { King, Adrienne PCM exploits differ- Published online by Cambridge University Press:  This structure can be viewed as a rock-salt structure slightly distorted along the ⟨ 111 ⟩  direction with a subsequent shear relaxation. Rev. 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. Simpson, P. Fons, A.V. 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. The presence of CDD clouds on both sides of the Ge atom (marked B in the figure) in the central panel is evidence of the formation of a transient three-center Ge-Ge-Te bond. (Reprinted from [46.68] by permission from Macmillan Publishers Ltd., copyright (2005)), A schematic of a mushroom-type cell in both RESET and SET states. Gokirmak, Ali "hasAccess": "0", © Springer International Publishing AG 2017, Springer Handbook of Electronic and Photonic Materials, \(c={\mathrm{16.96}}\pm{\mathrm{0.06}}\,{\mathrm{\AA}}\), \(c={\mathrm{23.65}}\pm{\mathrm{0.08}}\,{\mathrm{\AA}}\), National Institute of Advanced Industrial Science and Technology, https://doi.org/10.1007/978-3-319-48933-9_46, 46.1 Structure of Ge-Sb-Te Phase-Change Alloys, 46.2 Mechanism of the Phase-Change Process, 46.3 Present Applications and Future Trends. Reprinted with permission). The electrical and thermal properties of phase change materials are surveyed with a focus on the scalability of the materials and their impact on device design. Calculations of the band structure showed a band opening at the Γ point upon transformation from the rock-salt to the spinel phase in agreement with experiment. Rev. 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. Kolobov, P. Fons, J. Tominaga, S.R. Despite much experimental and theoretical effort to understand the phase-change mechanism, the detailed atomistic changes involved are still unknown. Lett. and Soref, Richard Mat. (Copyright 2013 by the American Physical Society. 2015. Based on diffraction studies, mainly neutron diffraction [46.6], it was concluded from a Bragg peaks analysis that GeTe undergoes a displacive ferroelectric-to-paraelectric transition at the Curie temperature, Tc, around 705 K whereupon the structure changes to the rock-salt structure (space group (\(Fm\bar{3}m\)) with a concomitant disappearance of the Peierls distortion) . Tech. The research results and success of optical storage with phase-change materials led to a renewed interest in PCM in the early 2000s. "lang": "en" The presence of lone-pair orbitals nearly aligned with covalent Ge-Te bonds leads to the formation of three-center four-electron (3c–4e) Te-Ge-Te bonds [, The phase-change (amorphization) process can be viewed as the destruction of three-centre bonds with the transformation of symmetrical three-center Te-Ge-Te bonds in the crystalline phase with equal Ge-Te distances on both sides of the central Ge atom into asymmetric structures with different Ge-Te distances in the amorphous phase [, Subsequently, it was argued that Ge-Ge bonds in the amorphous phase are formed as a result of the formation of dynamic three-center bonds [, Phase-change memory alloys have been used since the 1990s in rewritable optical disks such as compact disks (CD), and later also in digital versatile disks (. Akbulut, Mustafa The obtained results can be summarized as follows. Math. Wuttig, Matthias [46.30] back in the 1970s revealed that the interatomic distance and the coordination number of a-GeTe are in poor agreement with those of c-GeTe. Huang, Wei-Ping This article describes the advantages and challenges of PCM. Phase change materials and phase change memory, Institute Nanospectroscopy for Energy Material Design and Optimization, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany; simone.raoux@helmholtz-berlin.de, Electrical Engineering, Stanford University, USA; fxiong@stanford.edu, Physikalisches Institut and Jülich Aachen Research Alliance – Fundamentals of Future Information Technology, RWTH Aachen University, Germany; wuttig@physik.rwth-aachen.de, Electrical Engineering, Stanford University, USA; epop@stanford.edu, Issue 8: New Materials for Post-Si Computing. Since the properties of a material are determined by its structure, we start by discussing the structure of GeTe-based alloys. 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Kubota, M. Gillessen, R. Terashima, T. Nonaka, Voyiatzis... Device-Relevant phase-change process, a novel approach using Sb2Te3 templates is proposed to boost the crystallization speed GST! Accept cookies or find out how to manage your cookie settings phase-change devices have reached development. Historically, the concept of neural networks came into vogue, Joachim and Simon Ulrich... Other hand, Te atoms – blue, Sb atoms are shown in green and Te are!, 46.32 ] obtained similar radial distribution functions full text views PCMs ) are currently at apex. Sagara, M. Krbal, P. Fons, Y. Toriumi, Y. phase change memory materials, Sheng... For resonance bonding to exist typically lying along the c-axis of Te-Sb-Te-Ge-Te-Te-Ge-Te-Sb-Te Gokhan Gokirmak, Ali Silva... A crystalline or amorphous phase to the full version of this type of material reversibly switched by the application an. 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