Solids. Rev. "comments": true, Shamoto, K. Kodama, S. Iikubo, T.U. T. Matsunaga, N. Yamada, Y. Kubota: Acta Cryst. In optical memory, the phase-change material is heated with a laser source and it is the contrast in optical reflectivity between the amorphous and crystalline phases that is used to store information. 14 August 2014. In particular, they found the Ge-Te bond to be 2.62 Å and the Sb-Te bond to be 2.84 Å (as compared to 2.83 and 2.94 Å, respectively in the crystalline phase), that is, the bonds are shorter in the amorphous phase. 2015. Ge atoms are shown in green and Te atoms are shown in orange. Its recrystallization time is 20 nanoseconds, allowing bitrates of up to 35 Mbit /s to be written and direct overwrite capability up to 10 6 cycles. Phys. Silva, Helena Feature Flags: { Gerlach, J. W. Wiemer, Claudia Rep. (2015), doi: A.A. Burkov, L. Balents: Phys. T. Matsunaga, R. Kojima, N. Yamada, K. Kifune, Y. Kubota, Y. Tabata, M. Takata: Inorg. Phase‐Change Memory Materials by Design: A Strain Engineering Approach. In this phase, Ge and Te atoms are sixfold coordinated to each other with subsets of three shorter (2.83 Å) and three longer (3.15 Å) bonds often described as a Peierls distortion [46.5] due to the reduced coupling between the orthogonal p-type orbitals that constitute the basis for bonding in GeTe. B, T. Chattopadhyay, J. Boucherle, H. Von Schnering: J. Phys. Phase change memory (PCM) is a type of non-volatile RAM that stores data by changing the state of the material used, meaning it changes back and forth between amorphous and crystalline states on a microscopic level. 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. However, since the 1990s, phase-change materials became widely used in optical memory devices and still currently serve as the information storage medium in CDs, DVDs and Blu-Ray disks . Electrical cell designs for the large-scale integration of phase-change devices have reached commercial development. 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. A natural PCM is water/ice. SPIE Digital Library Proceedings. S.R. Solids, M. Paesler, D. Baker, G. Lucovsky, A. Edwards, P. Taylor: J. Phys. Data Storage Mater. PCM is considered an emerging technology. Nanotech. Phys. The Ge-Te bond length (2.59 Å) was also found to be consistent with the 4(Ge):2(Te) bonding geometry [46.35]. Mat. Phase change materials and phase change memory, Institute Nanospectroscopy for Energy Material Design and Optimization, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany; [email protected], Electrical Engineering, Stanford University, USA; [email protected], Physikalisches Institut and Jülich Aachen Research Alliance – Fundamentals of Future Information Technology, RWTH Aachen University, Germany; [email protected], Electrical Engineering, Stanford University, USA; [email protected], Issue 8: New Materials for Post-Si Computing. Phys. Gupta, S K Most interestingly, the minimum value of the white-line intensity during the amorphization process is significantly higher than that corresponding to the static liquid state [46.63] suggesting that Ge2Sb2Te5 does not melt in the conventional sense upon its transformation from the crystalline to the amorphous phase [46.62]. These devices are not solid state. Solids. A rather special situation is created when Ge bonds to a chalcogen. Lett. 2. Recently, however, the potential has been demonstrated for using phase‐change devices as the basis for new forms of brain‐like computing, by exploiting their multilevel resistance capability to provide electronic mimics of biological synapses. Phys. K.V. A phase-change materialabsorbs and/or releases large amount of energy in the process, r… 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. Phase-change memory (PCM) is a form of computer random-access memory ( RAM ) that stores data by altering the state of the matter from which the device is fabricated. This memory is a transistor NVM with no transistor under the resistive element, but since the 2015 press release, it has been common belief that it is actually based on a phase-change material (PCM) memory. B. M. Xu, Y. Cheng, H. Sheng, E. Ma: Phys. Vacancies present in the structure deserve a dedicated paragraph. Simon, Ulrich Kolobov, P. Fons, T. Nakano, S. Murakami: Adv. Saito, Y. Mazzarello, Riccardo In the past, research on phase change materials mainly focused on adjusting their physical properties by adding additional chemical elements into the alloys. However, this resulted in very complex compositions that were difficult to create and maintain in memory devices of only a few nanometers in size. Singh, J About 60% of Ge atoms were found to be fourfold coordinated but only 34% were tetrahedrally bonded. 2015. As a result, two Sb atoms (shown in magenta in Fig. A.H. Edwards, A.C. Pineda, P.A. If long-range order is lost, the system will be unable to achieve resonant bonding [46.23]. Rarey, Jonathan E‐mail: [email protected], [email protected] Search for more papers by this author. Reprinted with permission), (a) Schematic of the formation of a tetrahedral Ge configuration. 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. Fourier transformed EXAFS spectra for Ge (a), Sb (b), and Te (c) K-edges for laser crystallized and laser amorphized Ge2Sb2Te5. © 2020 Springer Nature Switzerland AG. The threshold switching effect of phase change memory devices is typically parameterized by the threshold voltage at which this breakdown occurs. While in the crystalline phase the central Ge atom has covalent like interactions with four Te neighbors, in the amorphous phase, it is covalently bonded to only three Te atoms [46.59]. Lett. S. Hosokawa, Y. Hari, T. Kouchi, I. Ono, H. Sato, M. Taniguchi, A. Hiraya, Y. Takata, N. Kosugi, M. Watanabe: J. Phys.-Cond. Estimation of kinetic parameters for the phase change memory materials by DSC measurements Alexey Sherchenkov • Sergey Kozyukhin • Alexey Babich Received: 26 November 2013/Accepted: 31 May 2014 PCM Applications and an Outlook to the Future. "languageSwitch": true While the obtained bond lengths are significantly shorter than those expected from the experimental lattice parameters and the rock-salt symmetry, they are at the same time significantly longer that the sum of the corresponding covalent radii, which suggests that the bonds are not purely covalent. B. T. Matsunaga, P. Fons, A.V. Bhaskaran, Harish On the other hand, Te atoms can form two conventional covalent bonds with Sb atoms; its lone-pair electrons cannot be used. 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. Wennberg, Maren 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. and The fundamental mechanism for Phase-Change Memory was invented in the 1960s by Stanford Robert Ovshinsky. 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. 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. Rev. "metrics": true, Lupini, Andrew R. 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). Bond shortening in the as-deposited amorphous phase of Ge2Sb2Te5 has also been observed by high-energy x-ray scattering experiments [46.45]. Phase change memory uses a semiconductor alloy that can be changed rapidly between an ordered, crystalline phase having lower electrical resistance to a disordered, amorphous phase with much higher electrical resistance. Phase-change materials are Te-containing alloys, typically lying along the GeTe-Sb 2 Te 3 quasibinary tie line. Song, Y.-H. I. Petrov, R. Imamov, Z. Pinsker: Sov. T. Matsunaga, H. Morita, R. Kojima, N. Yamada, K. Kifune, Y. Kubota, Y. Tabata, J.-J. Sun, S.B. Kolobov, P. Fons, J. Tominaga, S.R. and The uniform crystalline structure of TST film is very benefit for the endurance characteristic. An Sb atom has one unpaired valence electron on each of its three p-orbitals and can thus form three conventional covalent bonds. B. Hyot, X. Biquard, L. Poupinet: Local structure of amorphous and crystalline GeTe and GeSbTe, Proc. Li, Le View all Google Scholar citations 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. Jung, K.J. 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. The change in beam cross-section is displayed at the bottom. In August 2004, Nanochip licensed PRAM technology for use in MEMS(micro-electric-mechanical-systems) probe storage devices. Mat. Eur. Sosso, J. Behler, M. Bernasconi: Phys. 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. The distortion present in GST alloys is usually referred to as Peierls distortion [46.5]. Difference in electron charge density for GeTe at 0 K and isolated pseudo-atoms. Saltzmann, Tobias Wang, Bingyao A way to ensure six bonds is by virtue of sharing the valence electrons among several bonds with less than two electrons per bond on average through resonance bonding, a concept that is described as follows. Zou, Hua Lett. Phys. Part of Springer Nature. As a result, if the melt is cooled slowly, the equilibrium crystalline phase is formed. In the low-temperature ferroelectric phase, GeTe possesses a rhombohedral structure with the space group R3m. In the 1980s with the pioneering work of Hopfield 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. and A large fraction of Ge atoms (≈ 33%) were found on tetrahedral sites. The first model that attempted to provide an atomistic description of the phase-change process was the umbrella-flip model [46.20]. T. Matsunaga, R. Kojima, N. Yamada, K. Kifune, Y. Kubota, M. Takata: Appl. Rev. The obtained results can be summarized as follows. The first simulation of the melt-quenched amorphous Ge2Sb2Te5 was reported by Caravati et al. Lotnyk, A. Ma, Evan Akola and Jones [46.51, 46.52] performed similar simulations using significantly larger cells (460 atom as opposed to the 270 atom of [46.49]) and carried out molecular dynamics simulations over hundreds of picoseconds, times that are comparable to the experimentally observed (ca. 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. A longer pulse of lower intensity reverts the material to the crystalline phase. Ge-Sb-Te materials are used in optical DVDs and non-volatile electronic memories (phase-change random-access memory). The scaling limits of PCM are addressed, and its performance is compared to competing existing and emerging memory technologies. 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. and 2016. Rev. Phase change materials have a large electrical contrast; for Fig. Kifune, Y. Verhelle: Vibrational modes and bonding in the Issue materials for... Access options below Vibrational modes and bonding in the lens system are shown in orange through phase change memory materials reversible transitions crystalline! A rather Special situation is created when Ge bonds to a chalcogen K Aswal, D K Gupta... Stable phase of Ge2Sb2Te5 based synapses exhibiting the spike-timing-dependent plasticity required for neuromorphic computing was reported in 2012 [ ]! Kwon, S. Kremers, M. Kuwahara, I. Katayama, T. Chattopadhyay, J. Lee Y.. 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