Source: https://www.nature.com/articles/s41578-018-0076-x?error=cookies_not_supported&code=4d21063b-e6e6-4964-9558-8d7498fdc86f
Timestamp: 2019-04-25 04:56:57+00:00

Document:
The global demand for data storage and processing has increased exponentially in recent decades. To respond to this demand, research efforts have been devoted to the development of non-volatile memory and neuro-inspired computing technologies. Chalcogenide phase-change materials (PCMs) are leading candidates for such applications, and they have become technologically mature with recently released competitive products. In this Review, we focus on the mechanisms of the crystallization dynamics of PCMs by discussing structural and kinetic experiments, as well as ab initio atomistic modelling and materials design. Based on the knowledge at the atomistic level, we depict routes to improve the parameters of phase-change devices for universal memory. Moreover, we discuss the role of crystallization in enabling neuro-inspired computing using PCMs. Finally, we present an outlook for future opportunities of PCMs, including all-photonic memories and processors, flexible displays with nanopixel resolution and nanoscale switches and controllers.
Gu, M., Zhang, Q. & Lamon, S. Nanomaterials for optical data storage. Nat. Rev. Mater. 1, 16070 (2016).
Big data needs a hardware revolution [editorial]. Nature 554, 145–146 (2018).
Does AI have a hardware problem? [editorial]. Nat. Electron. 1, 205–205 (2018).
Wong, H.-S. P. & Salahuddin, S. Memory leads the way to better computing. Nat. Nanotechnol. 10, 191–194 (2015).
Wuttig, M. & Yamada, N. Phase-change materials for rewriteable data storage. Nat. Mater. 6, 824–832 (2007).
Waser, R. & Aono, M. Nanoionics-based resistive switching memories. Nat. Mater. 6, 833–840 (2007).
Kent, A. D. & Worledge, D. C. A new spin on magnetic memories. Nat. Nanotechnol. 10, 187–191 (2015).
Scott, J. F. & de Araujo, C. A. P. Ferroelectric memories. Science 246, 1400–1405 (1989).
Pan, F., Gao, S., Chen, C., Song, C. & Zeng, F. Recent progress in resistive random access memories: materials, switching mechanisms, and performance. Mater. Sci. Eng. R 83, 1–59 (2014).
Mead, C. Neuromorphic electronic systems. Proc. IEEE 78, 1629–1636 (1990).
Merolla, P. A. et al. A million spiking-neuron integrated circuit with a scalable communication network and interface. Science 345, 668–673 (2014).
Service, R. F. The brain chip. Science 345, 614–616 (2014).
Yang, J. J., Strukov, D. B. & Stewart, D. R. Memristive devices for computing. Nat. Nanotechnol. 8, 13–24 (2013).
Burr, G. W. et al. Neuromorphic computing using non-volatile memory. Adv. Phys. X 2, 89–124 (2016).
Zidan, M. A., Strachan, J. P. & Lu, W. D. The future of electronics based on memristive systems. Nat. Electron. 1, 22–29 (2018).
Lankhorst, M. H. R., Ketelaars, B. W. & Wolters, R. A. Low-cost and nanoscale non-volatile memory concept for future silicon chips. Nat. Mater. 4, 347–352 (2005).
Tuma, T., Pantazi, A., Le Gallo, M., Sebastian, A. & Eleftheriou, E. Stochastic phase-change neurons. Nat. Nanotechnol. 11, 693–699 (2016).
Kolobov, A. V. et al. Understanding the phase-change mechanism of rewritable optical media. Nat. Mater. 3, 703–708 (2004).
Li, X.-B., Chen, N.-K., Wang, X.-P. & Sun, H.-B. Phase-change superlattice materials toward low power consumption and high density data storage: microscopic picture, working principles, and optimization. Adv. Funct. Mater. 28, 1803380 (2018).
Kwon, D.-H. et al. Atomic structure of conducting nanofilaments in TiO2 resistive switching memory. Nat. Nanotechnol. 5, 148–153 (2010).
Prezioso, M. et al. Training and operation of an integrated neuromorphic network based on metal-oxide memristors. Nature 521, 61–64 (2015).
Liu, S. et al. Eliminating negative-SET behavior by suppressing nanofilament overgrowth in cation-based memory. Adv. Mater. 28, 10623–10629 (2016).
Yang, Y. & Huang, R. Probing memristive switching in nanoionic devices. Nat. Electron. 1, 274–287 (2018).
Mangin, S. et al. Current-induced magnetization reversal in nanopillars with perpendicular anisotropy. Nat. Mater. 5, 210–215 (2006).
Torrejon, J. et al. Neuromorphic computing with nanoscale spintronic oscillators. Nature 547, 428–431 (2017).
Zhang, S. et al. Electric-field control of nonvolatile magnetization in Co40Fe40B20/Pb(Mg(1/3)Nb(2/3))0.7Ti0.3O3 structure at room temperature. Phys. Rev. Lett. 108, 137203 (2012).
Park, B. H. et al. Lanthanum-substituted bismuth titanate for use in non-volatile memories. Nature 401, 682–684 (1999).
Chanthbouala, A. et al. A ferroelectric memristor. Nat. Mater. 11, 860–864 (2012).
Liu, C. et al. A semi-floating gate memory based on van der Waals heterostructures for quasi-non-volatile applications. Nat. Nanotechnol. 13, 404–410 (2018).
Wang, M. et al. Robust memristors based on layered two-dimensional materials. Nat. Electron. 1, 130–136 (2018).
Rueckes, T. et al. Carbon nanotube-based nonvolatile random access memory for molecular computing. Science 289, 94–97 (2000).
Kim, K., Chen, C. L., Truong, Q., Shen, A. M. & Chen, Y. A carbon nanotube synapse with dynamic logic and learning. Adv. Mater. 25, 1693–1698 (2013).
Ouyang, J., Chu, C.-W., Szmanda, C. R., Ma, L. & Yang, Y. Programmable polymer thin film and non-volatile memory device. Nat. Mater. 3, 918–922 (2004).
van de Burgt, Y. et al. A non-volatile organic electrochemical device as a low-voltage artificial synapse for neuromorphic computing. Nat. Mater. 16, 414–418 (2017).
Hruska, J. Intel, Micron reveal Xpoint, a new memory architecture that could outclass DDR4 and NAND. ExtremeTech https://www.extremetech.com/extreme/211087-intel-micron-reveal-xpoint-a-new-memory-architecture-that-claims-to-outclass-both-ddr4-and-nand (2015).
Choe, J. Intel 3D XPoint memory die removed from Intel OptaneTM PCM (Phase Change Memory). TechInsights http://www.techinsights.com/about-techinsights/overview/blog/intel-3D-xpoint-memory-die-removed-from-intel-optane-pcm (2017).
Fong, S. W., Neumann, C. M. & Wong, H.-S. P. Phase-change memory — towards a storage-class memory. IEEE Trans. Electron Devices 64, 4374–4385 (2017).
Hruska, J. Intel announces new optane DC persistent memory. ExtremeTech https://www.extremetech.com/extreme/270270-intel-announces-new-optane-dc-persistent-memory (2018).
Wuttig, M. Towards a universal memory. Nat. Mater. 4, 265–266 (2005).
Rao, F. et al. Reducing the stochasticity of crystal nucleation to enable subnanosecond memory writing. Science 358, 1423–1427 (2017).
Salinga, M. et al. Monatomic phase change memory. Nat. Mater. 17, 681–685 (2018).
Ovshinsky, S. Reversible electrical switching phenomena in disordered structures. Phys. Rev. Lett. 21, 1450–1453 (1968).
Siegrist, T. et al. Disorder-induced localization in crystalline phase-change materials. Nat. Mater. 10, 202–208 (2011).
Zhang, W. et al. Role of vacancies in metal-insulator transitions of crystalline phase-change materials. Nat. Mater. 11, 952–956 (2012).
Zhang, W. et al. Density functional theory guided advances in phase-change materials and memories. MRS Bull. 40, 856–865 (2015).
Raty, J.-Y. et al. Aging mechanism of amorphous phase change materials. Nat. Commun. 6, 7467 (2015).
Gabardi, S., Caravati, S., Sosso, G. C., Behler, J. & Bernasconi, M. Microscopic origin of resistance drift in the amorphous state of the phase-change compound GeTe. Phys. Rev. B 92, 054201 (2015).
Shportko, K. et al. Resonant bonding in crystalline phase-change materials. Nat. Mater. 7, 653–658 (2008).
Wang, J.-J., Xu, Y.-Z., Mazzarello, R., Wuttig, M. & Zhang, W. A review on disorder-driven metal-insulator transition in crystalline vacancy-rich GeSbTe phase-change materials. Materials 10, 862 (2017).
Jeyasingh, R. et al. Ultrafast characterization of phase-change material crystallization properties in the melt-quenched amorphous phase. Nano Lett. 14, 3419–3426 (2014).
Wong, H.-S. P. et al. Phase change memory. Proc. IEEE 98, 2201 (2010).
Raoux, S., Welnic, W. & Ielmini, D. Phase change materials and their application to nonvolatile memories. Chem. Rev. 110, 240–267 (2010).
Raoux, S. & Wuttig, M. (eds) Phase Change Materials: Science and Applications (Springer US, 2008).
Waldecker, L. et al. Time-domain separation of optical properties from structural transitions in resonantly bonded materials. Nat. Mater. 14, 991–995 (2015).
Wright, C. D. Phase-change devices: crystal-clear neuronal computing. Nat. Nanotechol. 11, 655–656 (2016).
Kuzum, D., Jeyasingh, R. G., Lee, B. & Wong, H. S. Nanoelectronic programmable synapses based on phase change materials for brain-inspired computing. Nano Lett. 12, 2179–2186 (2012).
Li, Y. et al. Associative learning with temporal contiguity in a memristive circuit for large-scale neuromorphic networks. Adv. Elect. Mater. 1, 1500125 (2015).
Ovshinsky, S. R. The ovonic cognitive computer — a new paradigm. Presented at the 2004 European Phase Change and Ovonic Symposium (E/PCOS).
Wright, C. D., Wang, L., Aziz, M. M., Diosdado, J. A. V. & Ashwin, P. Phase-change processors, memristors and memflectors. Phys. Status Solidi B 249, 1978–1984 (2012).
Chua, L. O. Memristor — the missing circuit element. IEEE Trans. Circuit Theory 18, 507–519 (1971).
Chua, L. O. How we predicted the memristor. Nat. Electron. 1, 322–322 (2018).
Li, Y. et al. Ultrafast synaptic events in a chalcogenide memristor. Sci. Rep. 3, 1619 (2013).
Chen, M., Rubin, K. A. & Barton, R. W. Compound materials for reversible, phase-change optical data storage. Appl. Phys. Lett. 49, 502 (1986).
Yamada, N., Ohno, E., Nishiuchi, K., Akahira, N. & Takao, M. Rapid-phase transitions of GeTe-Sb2Te3 pseudobinary amorphous thin films for an optical disk memory. J. Appl. Phys. 69, 2849–2856 (1991).
Iwasaki, H. et al. Completely erasable phase-change optical disc. II. Application of Ag-In-Sb-Te mixed-phase system for rewritable compact disc compatible with CD-velocity and double CD-velocity. Jpn J. Appl. Phys. 32, 5241–5247 (1993).
Afonso, C. N., Solis, J., Catalina, F. & Kalpouzos, C. Ultrafast reversible phase-change in GeSb films for erasable optical storage. Appl. Phys. Lett. 60, 3123–3125 (1992).
Lencer, D. et al. A map for phase-change materials. Nat. Mater. 7, 972–977 (2008).
Wuttig, M., Deringer, V. L., Gonze, X., Bichara, C. & Raty, J.-Y. Incipient metals: functional materials with a unique bonding mechanism. Adv. Mater. 30, 1803777 (2018).
Zhu, M. et al. Unique bond breaking in crystalline phase change materials and the quest for metavalent bonding. Adv. Mater. 30, 1706735 (2018).
Lencer, D., Salinga, M. & Wuttig, M. Design rules for phase-change materials in data storage applications. Adv. Mater. 23, 2030–2058 (2011).
Meinders, E. R., Mijiritskii, A. V., van Pieterson, L. & Wuttig, M. Optical Data Storage: Phase-Change Media and Recording (Springer Netherlands, 2006).
Salinga, M. et al. Measurement of crystal growth velocity in a melt-quenched phase-change material. Nat. Commun. 4, 2371 (2013).
Kelton, K. F. & Greer, A. L. Nucleation in Condensed Matter: Applications in Materials and Biology (Elsevier, Oxford, 2010).
Kalb, J. A., Spaepen, F. & Wuttig, M. Kinetics of crystal nucleation in undercooled droplets of Sb− and Te-based alloys used for phase change recording. J. Appl. Phys. 98, 054910 (2005).
Kalb, J., Spaepen, F. & Wuttig, M. Calorimetric measurements of phase transformations in thin films of amorphous Te alloys used for optical data storage. J. Appl. Phys. 93, 2389 (2003).
Loke, D. et al. Breaking the speed limits of phase-change memory. Science 336, 1566–1569 (2012).
Lee, B. S. et al. Observation of the role of subcritical nuclei in crystallization of a glassy solid. Science 326, 980–984 (2009).
Zhang, B. et al. Element-resolved atomic structure imaging of rocksalt Ge2Sb2Te5 phase-change material. Appl. Phys. Lett. 108, 191902 (2016).
Matsunaga, T. et al. From local structure to nanosecond recrystallization dynamics in AgInSbTe phase-change materials. Nat. Mater. 10, 129–134 (2011).
Jones, R. O. Density functional theory: its origins, rise to prominence, and future. Rev. Mod. Phys. 87, 897–923 (2015).
Massobrio, C., Du, J., Bernasconi, M. & Salmon, P. S. (eds) Molecular Dynamics Simulations of Disordered Materials: From Network Glasses to Phase-Change Memory Alloys (Springer International Publishing, Switzerland, 2015).
Caravati, S., Bernasconi, M., Kühne, T. D., Krack, M. & Parrinello, M. Coexistence of tetrahedral- and octahedral-like sites in amorphous phase change materials. Appl. Phys. Lett. 91, 171906 (2007).
Akola, J. & Jones, R. Structural phase transitions on the nanoscale: the crucial pattern in the phase-change materials Ge2Sb2Te5 and GeTe. Phys. Rev. B 76, 235201 (2007).
Xu, M., Cheng, Y., Sheng, H. & Ma, E. Nature of atomic bonding and atomic structure in the phase-change Ge2Sb2Te5 glass. Phys. Rev. Lett. 103, 195502 (2009).
Bouzid, A., Ori, G., Boero, M., Lampin, E. & Massobrio, C. Atomic-scale structure of the glassy Ge2Sb2Te5 phase change material: a quantitative assessment via first-principles molecular dynamics Phys. Rev. B 96, 224204 (2017).
Mazzarello, R., Caravati, S., Angioletti-Uberti, S., Bernasconi, M. & Parrinello, M. Signature of tetrahedral Ge in the Raman spectrum of amorphous phase-change materials. Phys. Rev. Lett. 104, 085503 (2010).
Deringer, V. L. et al. Bonding nature of local structural motifs in amorphous GeTe. Angew. Chem. Int. Ed. 53, 10817–10820 (2014).
Mitrofanov, K. V. et al. Ge L3-edge X-ray absorption near-edge structure study of structural changes accompanying conductivity drift in the amorphous phase of Ge2Sb2Te5. J. Appl. Phys. 115, 173501 (2014).
Hirata, A., Ichitsubo, T., Guan, P. F., Fujita, T. & Chen, M. W. Distortion of local atomic structures in amorphous Ge-Sb-Te phase change materials. Phys. Rev. Lett. 120, 205502 (2018).
Kohara, S. et al. Structural basis for the fast phase change of Ge2Sb2Te5: ring statistics analogy between the crystal and amorphous states. Appl. Phys. Lett. 89, 201910 (2006).
Kühne, T., Krack, M., Mohamed, F. & Parrinello, M. Efficient and accurate Car-Parrinello-like approach to Born-Oppenheimer molecular dynamics. Phys. Rev. Lett. 98, 066401 (2007).
Hutter, J., Iannuzzi, M., Schiffmann, F. & VandeVondele, J. cp2k:atomistic simulations of condensed matter systems. Wiley Interdiscip. Rev. Comput. Mol. Sci. 4, 15–25 (2014).
CPMD. http://www.cpmd.org, copyright IBM Corp. 1990–2015, copyright MPI für Festkörperforschung Stuttgart 1997–2001.
Hegedüs, J. & Elliott, S. R. Microscopic origin of the fast crystallization ability of Ge-Sb-Te phase-change memory materials. Nat. Mater. 7, 399–405 (2008).
Lee, T. H. & Elliott, S. R. Ab initio computer simulation of the early stages of crystallization: application to Ge2Sb2Te5 phase-change materials. Phys. Rev. Lett. 107, 145702 (2011).
Skelton, J. M., Pallipurath, A. R., Lee, T.-H. & Elliott, S. R. Atomistic origin of the enhanced crystallization speed and n-type conductivity in bi-doped Ge-Sb-Te phase-change materials. Adv. Funct. Mater. 24, 7291–7300 (2014).
Kalikka, J., Akola, J., Larrucea, J. & Jones, R. O. Nucleus-driven crystallization of amorphous Ge2Sb2Te5: a density functional study. Phys. Rev. B 86, 144113 (2012).
Kalikka, J., Akola, J. & Jones, R. O. Simulation of crystallization in Ge2Sb2Te5: a memory effect in the canonical phase-change material. Phys. Rev. B 90, 184109 (2014).
Kalikka, J., Akola, J. & Jones, R. O. Crystallization processes in the phase change material Ge2Sb2Te5: unbiased density functional/molecular dynamics simulations. Phys. Rev. B 94, 134105 (2016).
Branicio, P. S. et al. Atomistic insights into the nanosecond long amorphization and crystallization cycle of nanoscale Ge2Sb2Te5: an ab initio molecular dynamics study. Phys. Rev. Mater. 2, 043401 (2018).
Bai, K., Tan, T. L., Branicio, P. S. & Sullivan, M. B. Time-temperature-transformation and continuous-heating-transformation diagrams of GeSb2Te4 from nanosecond-long ab initio molecular dynamics simulations. Acta Mater. 121, 257–265 (2016).
Akola, J. & Jones, R. O. Speeding up crystallization. Science 358, 1386–1386 (2017).
Wang, W.-J. et al. Fast phase transitions induced by picosecond electrical pulses on phase change memory cells. Appl. Phys. Lett. 93, 043121 (2008).
Zheng, Y. et al. Direct observation of metastable face-centered cubic Sb2Te3 crystal. Nano Res. 9, 3453–3462 (2016).
Caravati, S., Bernasconi, M. & Parrinello, M. First-principles study of liquid and amorphous Sb2Te3. Phys. Rev. B 81, 014201 (2010).
Guo, Y.-R. et al. Structural signature and transition dynamics of Sb2Te3 melt upon fast cooling. Phys. Chem. Chem. Phys. 20, 11768–11775 (2018).
Zhu, M. et al. One order of magnitude faster phase change at reduced power in Ti-Sb-Te. Nat. Commun. 5, 4086 (2014).
Rao, F. et al. Direct observation of titanium-centered octahedra in titanium-antimony-tellurium phase-change material. Nat. Commun. 6, 10040 (2015).
Dronskowski, R. & Blöchl, P. E. Crystal orbital Hamilton populations (COHP): energy-resolved visualization of chemical bonding in solids based on density-functional calculations. J. Phys. Chem. 97, 8617–8624 (1993).
Deringer, V. L., Tchougreeff, A. L. & Dronskowski, R. Crystal orbital Hamilton population (COHP) analysis as projected from plane-wave basis sets. J. Phys. Chem. A 115, 5461–5466 (2011).
Maintz, S., Deringer, V. L., Tchougréeff, A. L. & Dronskowski, R. Analytic projection from plane-wave and PAW wavefunctions and application to chemical-bonding analysis in solids. J. Comput. Chem. 34, 2557–2567 (2013).
Maintz, S., Deringer, V. L., Tchougreeff, A. L. & Dronskowski, R. LOBSTER: a tool to extract chemical bonding from plane-wave based DFT. J. Comput. Chem. 37, 1030–1035 (2016).
Nascimento, M. L. F. & Zanotto, E. D. Mechanisms and dynamics of crystal growth, viscous flow, and self-diffusion in silica glass. Phys. Rev. B 73, 024209 (2006).
Wuttig, M. & Salinga, M. Phase-change materials: fast transformers. Nat. Mater. 11, 270–271 (2012).
Orava, J., Greer, A. L., Gholipour, B., Hewak, D. W. & Smith, C. E. Characterization of supercooled liquid Ge2Sb2Te5 and its crystallization by ultrafast-heating calorimetry. Nat. Mater. 11, 279–283 (2012).
Ronneberger, I., Zhang, W., Eshet, H. & Mazzarello, R. Crystallization properties of the Ge2Sb2Te5 phase-change compound from advanced simulations. Adv. Funct. Mater. 25, 6407–6413 (2015).
Ronneberger, I., Zhang, W. & Mazzarello, R. Crystal growth of Ge2Sb2Te5 at high temperatures. MRS Commun. 8, 1018–1023 (2018).
Laio, A. & Parrinello, M. Escaping free-energy minima. Proc. Natl Acad. Sci. USA 99, 12562–12566 (2002).
ten Wolde, P., Ruiz-Montero, M. J. & Frenkel, D. Simulation of homogeneous crystal nucleation close to coexistence. Faraday Discuss. 104, 93–110 (1996).
Zhang, W. et al. How fragility makes phase-change data storage robust: insights from ab initio simulations. Sci. Rep. 4, 6529 (2014).
Hegedus, J. & Elliott, S. R. Computer-simulation design of new phase-change memory materials. Phys. Status Solidi A 207, 510–515 (2010).
Sosso, G. C., Miceli, G., Caravati, S., Behler, J. & Bernasconi, M. Neural-network interatomic potential for the phase change material GeTe. Phys. Rev. B 85, 174103 (2012).
Sosso, G. et al. Fast crystallization of the phase change compound GeTe by large-scale molecular dynamics simulations. J. Phys. Chem. Lett. 4, 4241–4246 (2013).
Sosso, G. C., Behler, J. & Bernasconi, M. Breakdown of Stokes-Einstein relation in the supercooled liquid state of phase change materials. Phys. Status Solidi B 249, 1880–1885 (2012).
Sosso, G., Colombo, J., Behler, J., Del Gado, E. & Bernasconi, M. Dynamical Heterogeneities in the supercooled liquid state of the phase change compound GeTe. J. Phys. Chem. B 118, 13621 (2014).
Zipoli, F. & Curioni, A. Reactive potential for the study of phase-change materials: GeTe. New J. Phys. 15, 123006 (2013).
Zipoli, F., Krebs, D. & Curioni, A. Structural origin of resistance drift in amorphous GeTe. Phys. Rev. B 93, 115201 (2016).
Gabardi, S. et al. Atomistic simulations of the crystallization and aging of GeTe nanowires. J. Phys. Chem. C 121, 23827–23838 (2017).
Rupp, M. Machine learning for quantum mechanics in a nutshell. Int. J. Quant. Chem. 115, 1058–1073 (2015).
Behler, J. First principles neural network potentials for reactive simulations of large molecular and condensed systems. Angew. Chem. Int. Ed. 56, 12828–12840 (2017).
Deringer, V. L. et al. Realistic atomistic structure of amorphous silicon from machine-learning-driven molecular dynamics. J. Phys. Chem. Lett. 9, 2879–2885 (2018).
Deringer, V. L. & Csányi, G. Machine learning based interatomic potential for amorphous carbon. Phys. Rev. B 95, 094203 (2017).
Mocanu, F. C. et al. Modeling the phase-change memory material Ge2Sb2Te5 with a machine-learned interatomic potential. J. Phys. Chem. B 122, 8998–9006 (2018).
Ciocchini, N., Cassinerio, M., Fugazza, D. & Ielmini, D. Evidence for non-Arrhenius kinetics of crystallization in phase change memory devices. IEEE Trans. Electron Devices 60, 3767–3774 (2013).
Chen, Y. et al. Unraveling the crystallization kinetics of supercooled liquid GeTe by ultrafast calorimetry. Cryst. Growth Des. 17, 3687–3693 (2017).
Chen, B., de Wal, D., ten Brink, G. H., Palasantzas, G. & Kooi, B. J. Resolving crystallization kinetics of GeTe phase-change nanoparticles by ultrafast calorimetry. Cryst. Growth Des. 18, 1041–1046 (2018).
Debenedetti, P. G. & Stillinger, F. H. Supercooled liquids and the glass transition. Nature 410, 259–267 (2001).
Angell, C. A. Formation of glasses from liquids and biopolymers. Science 267, 1924–1935 (1995).
Kelton, K. F. Kinetic and structural fragility-a correlation between structures and dynamics in metallic liquids and glasses. J. Phys. Condens. Matter 29, 023002 (2017).
Shelby, R. M. & Raoux, S. Crystallization dynamics of nitrogen-doped Ge2Sb2Te5. J. Appl. Phys. 105, 104902 (2009).
Lee, T. H., Loke, D. & Elliott, S. R. Microscopic mechanism of doping-induced kinetically constrained crystallization in phase-change materials. Adv. Mater. 27, 5477–5483 (2015).
Cho, J.-Y. et al. The phase-change kinetics of amorphous Ge2Sb2Te5 and device characteristics investigated by thin-film mechanics. Acta Mater. 94, 143–151 (2015).
Orava, J., Hewak, D. W. & Greer, A. L. Fragile-to-strong crossover in supercooled liquid Ag-In-Sb-Te studied by ultrafast calorimetry. Adv. Funct. Mater. 25, 4851–4858 (2015).
Orava, J., Weber, H., Kaban, I. & Greer, A. L. Viscosity of liquid Ag-In-Sb-Te: evidence of a fragile-to-strong crossover. J. Chem. Phys. 144, 194503 (2016).
Kalb, J., Spaepen, F., Leervad Pedersen, T. P. & Wuttig, M. Viscosity and elastic constants of thin films of amorphous Te alloys used for optical data storage. J. Appl. Phys. 94, 4908–4912 (2003).
Kalb, J., Spaepen, F. & Wuttig, M. Atomic force microscopy measurements of crystal nucleation and growth rates in thin films of amorphous Te alloys. Appl. Phys. Lett. 84, 5240 (2004).
Eising, G., Van Damme, T. & Kooi, B. J. Unraveling crystal growth in GeSb phase-change films in between the glass-transition and melting temperatures. Cryst. Growth Des. 14, 3392–3397 (2014).
Orava, J., Greer, A. L., Gholipour, B., Hewak, D. W. & Smith, C. E. Ultra-fast calorimetry study of Ge2Sb2Te5 crystallization between dielectric layers. Appl. Phys. Lett. 101, 091906 (2012).
Li, Z., Si, C., Zhou, J., Xu, H. & Sun, Z. Yttrium-doped Sb2Te3: a promising material for phase-change memory. ACS Appl. Mater. Interfaces 8, 26126–26134 (2016).
Cheng, Y. & Ma, E. Atomic-level structure and structure-property relationship in metallic glasses. Prog. Mater. Sci. 56, 379–473 (2011).
Greer, A. L. New horizons for glass formation and stability. Nat. Mater. 14, 542–546 (2015).
Mattsson, J. et al. Soft colloids make strong glasses. Nature 462, 83–86 (2009).
Bruns, G. et al. Nanosecond switching in GeTe phase change memory cells. Appl. Phys. Lett. 95, 043108 (2009).
Im, D. H. et al. A unified 7.5nm dash-type confined cell for high performance PRAM device. Presented at the 2008 IEEE International Electron Devices Meeting (IEDM).
Behrndt, K. H. Formation of amorphous films. J. Vac. Sci. Technol. 7, 385–398 (1970).
Hauser, J. J. Hopping conductivity in amorphous antimony. Phys. Rev. B 9, 2623–2626 (1974).
Sohn, S. et al. Nanoscale size effects in crystallization of metallic glass nanorods. Nat. Commun. 6, 8157 (2015).
Raoux, S., Jordan-Sweet, J. L. & Kellock, A. J. Crystallization properties of ultrathin phase change film. J. Appl. Phys. 103, 114310 (2008).
Simpson, R. E. et al. Toward the ultimate limit of phase change in Ge2Sb2Te5. Nano Lett. 10, 414–419 (2010).
Caldwell, M. A., Raoux, S., Wang, R. Y., Philip Wong, H. S. & Milliron, D. J. Synthesis and size-dependent crystallization of colloidal germanium telluride nanoparticles. J. Mater. Chem. 20, 1285 (2010).
Chen, B., ten Brink, G. H., Palasantzas, G. & Kooi, B. J. Size-dependent and tunable crystallization of GeSbTe phase-change nanoparticles. Sci. Rep. 6, 39546 (2016).
Lee, S.-H., Jung, Y. & Agarwal, R. Size-dependent surface-induced heterogeneous nucleation driven phase-change in Ge2Sb2Te5 nanowires. Nano Lett. 8, 3303–3309 (2008).
Wu, W. et al. Crystallization characteristic and scaling behavior of germanium antimony thin films for phase change memory. Nanoscale 10, 7228–7237 (2018).
Zhang, W. & Ma, E. Phase-change memory: single-element glass to record data. Nat. Mater. 17, 654–655 (2018).
Yu, S. & Chen, P.-Y. Emerging memory technologies recent trends and prospects. IEEE Solid State Circuits Mag. 8, 43–56 (2016).
Kim, I. S. et al. High performance PRAM cell scalable to sub-20nm technology with below 4F2 cell size, extendable to DRAM applications [abstract 19.3]. Presented at the 2010 VLSI Technology Symposium.
Kim, W. et al. ALD-based confined PCM with a metallic liner toward unlimited endurance [abstract 4.2]. Presented at the 2016 IEEE International Electron Devices Meeting (IEDM).
Pedersen, T. et al. Mechanical stresses upon crystallization in phase change materials. Appl. Phys. Lett. 79, 3597 (2001).
Xie, Y. et al. Self-healing of a confined phase change memory device with a metallic surfactant layer. Adv. Mater. 30, 1705587 (2018).
Wu, Q. et al. Increasing the atomic packing efficiency of phase-change memory glass to reduce the density change upon crystallization. Adv. Electron. Mater. 4, 1800127 (2018).
Lung, H.-L. Toward the unlimited cycling endurance of phase-change memory. Presented at the 2017 European Phase Change and Ovonic Symposium (E\PCOS).
Ahn, C. Energy-efficient phase-change memory with graphene as a thermal barrier. Nano Lett. 15, 6809–6814 (2015).
Kim, C. Fullerene thermal insulation for phase change memory. Appl. Phys. Lett. 92, 013109 (2008).
Xiong, F. Self-aligned nanotube-nanowire phase change memory. Nano Lett. 13, 464–469 (2013).
Xiong, F., Liao, A. D., Estrada, D. & Pop, E. Low-power switching of phase-change materials with carbon nanotube electrodes. Science 332, 568–570 (2011).
Ahn, E. C., Wong, H.-S. P. & Pop, E. Carbon nanomaterials for non-volatile memories. Nat. Rev. Mater. 3, 18009 (2018).
Adler, D., Henisch, H. K. & Mott, S. N. The mechanism of threshold switching in amorphous alloys. Rev. Mod. Phys. 50, 209–220 (1978).
Adler, D., Shur, M. S., Silver, M. & Ovshinsky, S. R. Threshold switching in chalcogenide-glass thin films. J. Appl. Phys. 51, 3289–3309 (1980).
Redaelli, A. et al. Electronic switching effect and phase change transition in chalcogenide materials. IEEE Electron Device Lett. 25, 684 (2004).
Zalden, P. et al. Picosecond electric-field-induced threshold switching in phase-change materials. Phys. Rev. Lett. 117, 067601 (2016).
Anbarasu, M., Wimmer, M., Bruns, G., Salinga, M. & Wuttig, M. Nanosecond threshold switching of GeTe6 cells and their potential as selector devices. Appl. Phys. Lett. 100, 143505 (2012).
Ielmini, D., Lacaita, A. L. & Mantegazza, D. Recovery and drift dynamics of resistance and threshold voltages in phase-change memories. IEEE Trans. Electron Devices 54, 308–315 (2007).
Singh, S., Ediger, M. D. & de Pablo, J. J. Ultrastable glasses from in silico vapour deposition. Nat. Mater. 12, 139–144 (2013).
Kim, S. et al. A phase change memory cell with metallic surfactant layer as a resistance drift stabilizer [abstract 30.7]. Presented 2013 IEEE International Electron Devices Meeting (IEDM).
Koelmans, W. W. et al. Projected phase-change memory devices. Nat. Commun. 6, 8181 (2015).
Ambrogio, S. et al. Equivalent-accuracy accelerated neural network training using analogue memory. Nature 558, 60–67 (2018).
Sebastian, A. et al. Tutorial: brain-inspired computing using phase-change memory devices. J. Appl. Phys. 124, 111101 (2018).
Hebb, D. O. The Organization of Behavior: A Neuropsychological Theory (Wiley, 1949).
Burr, G. W. et al. Experimental demonstration and tolerancing of a large-scale neural network (165 000 synapses) using phase-change memory as the synaptic weight element. IEEE Trans. Electron Devices 62, 3498–3507 (2015).
Suri, M. et al. Addition of HfO2 interface layer for improved synaptic performance of phase change memory (PCM) devices. Solid State Electron. 79, 227–232 (2013).
Boybat, I. et al. Neuromorphic computing with multi-memristive synapses. Nat. Commun. 9, 2514 (2018).
Skelton, J. M., Loke, D., Lee, T. & Elliott, S. R. Ab initio molecular-dynamics simulation of neuromorphic computing in phase-change memory materials. ACS Appl. Mater. Interfaces 7, 14223–14230 (2015).
Le Gallo, M. et al. Mixed-precision in-memory computing. Nat. Electron. 1, 246–253 (2018).
Wuttig, M., Bhaskaran, H. & Taubner, T. Phase-change materials for non-volatile photonic applications. Nat. Photon. 11, 465–476 (2017).
Ríos, C., Hosseini, P., Wright, C. D., Bhaskaran, H. & Pernice, W. H. On-chip photonic memory elements employing phase-change materials. Adv. Mater. 26, 1372–1377 (2014).
Ríos, C. et al. Integrated all-photonic non-volatile multi-level memory. Nat. Photon. 9, 725–732 (2015).
Zhang, Q. et al. Broadband nonvolatile photonic switching based on optical phase change materials: beyond the classical figure-of-merit. Opt. Lett. 43, 94–97 (2018).
Cheng, Z., Ríos, C., Pernice, W. H. P., Wright, C. D. & Bhaskaran, H. On-chip photonic synapse. Sci. Adv. 3, e1700160 (2017).
Feldmann, J. et al. Calculating with light using a chip-scale all-optical abacus. Nat. Commun. 8, 1256 (2017).
Hosseini, P., Wright, C. D. & Bhaskaran, H. An optoelectronic framework enabled by low-dimensional phase-change films. Nature 511, 206–211 (2014).
Ríos, C., Hosseini, P., Taylor, R. A. & Bhaskaran, H. Color depth modulation and resolution in phase-change material nanodisplays. Adv. Mater. 28, 4720–4726 (2016).
Polking, M. J. et al. Controlling localized surface plasmon resonances in GeTe nanoparticles using an amorphous-to-crystalline phase transition. Phys. Rev. Lett. 111, 037401 (2013).
Li, P. et al. Reversible optical switching of highly confined phonon-polaritons with an ultrathin phase-change material. Nat. Mater. 15, 870–875 (2016).
Wang, Q. et al. Optically reconfigurable metasurfaces and photonic devices based on phase change materials. Nat. Photon. 10, 60–65 (2015).
Sa, B. & Sun, Z. Electron interactions and Dirac fermions in graphene-Ge2Sb2Te5 superlattices. J. Appl. Phys. 115, 233714 (2014).
Kulju, S., Akola, J., Prendergast, D. & Jones, R. O. Tuning electronic properties of graphene heterostructures by amorphous-to-crystalline phase transitions. Phys. Rev. B 93, 195443 (2016).
Song, W.-D., Shi, L.-P., Miao, X.-S. & Chong, C.-T. Synthesis and characteristics of a phase-change magnetic material. Adv. Mater. 20, 2394–2397 (2008).
Li, Y. & Mazzarello, R. Magnetic contrast in phase-change materials doped with Fe impurities. Adv. Mater. 24, 1429–1433 (2012).
Zhang, W., Ronneberger, I., Li, Y. & Mazzarello, R. Magnetic properties of crystalline and amorphous phase-change materials doped with 3d impurities. Adv. Mater. 24, 4387–4391 (2012).
Skelton, J. M. & Elliott, S. R. In silico optimization of phase-change materials for digital memories: a survey of first-row transition-metal dopants for Ge2Sb2Te5. J. Phys. Condens. Matter 25, 205801 (2013).
The authors acknowledge Y.-X. Zhou and J.-J. Wang for their help with figure preparations and R. Feng for useful discussions. W.Z. thanks the support of the National Natural Science Foundation of China (61774123 and 51621063), 111 Project 2.0 (BP2018008), the Youth Thousand Talents Program of China, the Young Talent Support Plan, Xi’an Jiaotong University and the International Joint Laboratory for Micro/Nano Manufacturing and Measurement Technologies. R.M. and M.W. acknowledge funding from Deutsche Forschungsgemeinschaft within SFB 917 ‘Nanoswitches’. E.M. is supported at Johns Hopkins University by the US Department of Energy, Office of Basic Energy Sciences, Department of Materials Sciences and Engineering (DOE-BES-DMSE) under grant DE-FG02-13ER46056.
W.Z. researched the data and wrote the manuscript. R.M., M.W. and E.M. edited the manuscript. All authors made a substantial contribution to the discussion of content.

References: V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V.