Femtosecond x-ray diffraction reveals a liquid–liquid phase transition in phase-change materials

Structural switch for fast switching Phase-change materials are important for computer memory. They can quickly switch from glassy to crystalline using a thermal pulse and then lock in that structure for a long time at lower temperature. Zalden et al. probed the underlying atomic structure of two phase-change materials during this switching using ultrafast x-rays and simulations (see the Perspective by Rao et al.). A liquid-liquid phase transition in both materials allowed fast switching at high temperatures. The lower-temperature glass locks in the structure, allowing for long-term memory storage. Science, this issue p. 1062; see also p. 1032 Two phase-change materials have a liquid–liquid transition that allows both fast switching and long-term stability. In phase-change memory devices, a material is cycled between glassy and crystalline states. The highly temperature-dependent kinetics of its crystallization process enables application in memory technology, but the transition has not been resolved on an atomic scale. Using femtosecond x-ray diffraction and ab initio computer simulations, we determined the time-dependent pair-correlation function of phase-change materials throughout the melt-quenching and crystallization process. We found a liquid–liquid phase transition in the phase-change materials Ag4In3Sb67Te26 and Ge15Sb85 at 660 and 610 kelvin, respectively. The transition is predominantly caused by the onset of Peierls distortions, the amplitude of which correlates with an increase of the apparent activation energy of diffusivity. This reveals a relationship between atomic structure and kinetics, enabling a systematic optimization of the memory-switching kinetics.

[1]  Wei Zhang,et al.  Reducing the stochasticity of crystal nucleation to enable subnanosecond memory writing , 2017, Science.

[2]  H. Eugene Stanley,et al.  Phase behaviour of metastable water , 1992, Nature.

[3]  I. Kaban,et al.  Viscosity of liquid Ag-In-Sb-Te: Evidence of a fragile-to-strong crossover. , 2016, The Journal of chemical physics.

[4]  Pablo G. Debenedetti,et al.  Relationship between structural order and the anomalies of liquid water , 2001, Nature.

[5]  R. S. Allgaier,et al.  Introduction to the Theory of Liquid Metals , 1972 .

[6]  M. Breitwisch,et al.  Ultra-Thin Phase-Change Bridge Memory Device Using GeSb , 2006, 2006 International Electron Devices Meeting.

[7]  H. Wong,et al.  Ultrafast terahertz-induced response of GeSbTe phase-change materials , 2014 .

[8]  Y. Tsuchiya.  Thermodynamics of the structural changes in the liquid Ge-Te system around the Te-rich eutectic composition , 2002 .

[9]  M. Wuttig,et al.  Phase-change materials for rewriteable data storage. , 2007, Nature materials.

[10]  M. Wuttig,et al.  Simultaneous calorimetric and quick-EXAFS measurements to study the crystallization process in phase-change materials. , 2012, Journal of synchrotron radiation.

[11]  M. Wuttig,et al.  Atomic force microscopy measurements of crystal nucleation and growth rates in thin films of amorphous Te alloys , 2004 .

[12]  D. Turnbull.  Under what conditions can a glass be formed , 1969 .

[13]  Peter H. Poole,et al.  Fragile-to-strong transition and polyamorphism in the energy landscape of liquid silica , 2001, Nature.

[14]  Matthias Wuttig,et al.  Measurement of crystal growth velocity in a melt-quenched phase-change material , 2013, Nature Communications.

[15]  A. Tverjanovich,et al.  Heat of structural transformation at the semiconductor-metal transition in As2Te3 liquid , 1996 .

[16]  David T. Limmer,et al.  The putative liquid-liquid transition is a liquid-solid transition in atomistic models of water. II. , 2013, The Journal of chemical physics.

[17]  Aaron M. Lindenberg,et al.  How Supercooled Liquid Phase-Change Materials Crystallize: Snapshots after Femtosecond Optical Excitation , 2015 .

[18]  M. Parrinello,et al.  Coexistence of tetrahedral- and octahedral-like sites in amorphous phase change materials , 2007, 0708.1302.

[19]  Matthias Wuttig,et al.  How fragility makes phase-change data storage robust: insights from ab initio simulations , 2014, Scientific Reports.

[20]  Matthias Wuttig,et al.  Crystallization kinetics of sputter-deposited amorphous AgInSbTe films , 2001 .

[21]  F. Hellman,et al.  Specific heat and thermal conductivity of low-stress amorphous Si–N membranes , 2004 .

[22]  Valerio Pruneri,et al.  Time-domain separation of optical properties from structural transitions in resonantly bonded materials. , 2014, Nature materials.

[23]  Caroline Vigreux,et al.  Effect of composition on the properties of Te–Ge thick films deposited by co-thermal evaporation , 2010 .

[24]  B. L. Henke,et al.  X-Ray Interactions: Photoabsorption, Scattering, Transmission, and Reflection at E = 50-30,000 eV, Z = 1-92 , 1993 .

[25]  M. Asheghi,et al.  Thermal Boundary Resistance Measurements for Phase-Change Memory Devices , 2010, IEEE Electron Device Letters.

[26]  M. Stolpe,et al.  Microscopic evidence of the connection between liquid-liquid transition and dynamical crossover in an ultraviscous metallic glass former , 2018, Physical Review Materials.

[27]  C. Angell,et al.  Formation of Glasses from Liquids and Biopolymers , 1995, Science.

[28]  R. Takahashi,et al.  Relationship between Peierls distortion and medium-range order in Liquid Group-V elements and liquid Group-IV-VI compounds , 2010 .

[29]  Pierre-Yves Chewvalier.  A thermodynamic evaluation of the Ge-In, Ge-Pb, Ge-Sb, Ge-Tl and Ge-Zn systems , 1989 .

[30]  Matthias Wuttig,et al.  Resonant bonding in crystalline phase-change materials. , 2008, Nature materials.

[31]  M. O'Keefe,et al.  Intensity of diffracted intensities , 2006 .

[32]  C. Angell,et al.  Water II is a "strong" liquid , 1993 .

[33]  Matthias Wuttig,et al.  Incipient Metals: Functional Materials with a Unique Bonding Mechanism , 2017, Advanced materials.

[34]  A. Barnes,et al.  Neutron and x-ray diffraction studies of liquids and glasses , 2005 .

[35]  Tobias Van Damme,et al.  Unraveling Crystal Growth in GeSb Phase-Change Films in between the Glass-Transition and Melting Temperatures , 2014 .

[36]  S. Sastry,et al.  Liquid–liquid critical point in supercooled silicon , 2011, 1103.3473.

[37]  S. Bennington,et al.  Pressure-induced suppression of the Peierls distortion of liquid As and GeX (X=S,Se,Te) , 2009 .

[38]  M. Wuttig,et al.  Atomic structure of amorphous and crystallized Ge15Sb85 , 2010 .

[39]  M. Wuttig,et al.  Characteristic Ordering in Liquid Phase‐Change Materials , 2008 .

[40]  Garrett J. Coleman,et al.  Glass Transitions, Semiconductor-Metal Transitions, and Fragilities in Ge-V-Te (V = As, Sb) Liquid Alloys: The Difference One Element Can Make , 2016, 1610.08164.

[41]  N. Mott,et al.  Localized States in Disordered Lattices , 1967, May 1.

[42]  Determination of specific heat with a simple inverse approach , 2003 .

[43]  Mehdi Asheghi,et al.  Ultrafast characterization of phase-change material crystallization properties in the melt-quenched amorphous phase. , 2014, Nano letters.

[44]  Martin Hilbert,et al.  The World’s Technological Capacity to Store, Communicate, and Compute Information , 2011, Science.

[45]  K. Goodson,et al.  Measurement of the Thermal Conductivity and Heat Capacity of Freestanding Shape Memory Thin Films Using the 3ω Method , 2008 .

[46]  K. Binder.  Simulations clarify when supercooled water freezes into glassy structures , 2014, Proceedings of the National Academy of Sciences.

[47]  A. Lindenberg,et al.  Ultrafast sub-threshold photo-induced response in crystalline and amorphous GeSbTe thin films , 2013 .

[48]  P. Debenedetti,et al.  Metastable liquid–liquid transition in a molecular model of water , 2014, Nature.

[49]  Matthias Wuttig,et al.  Calorimetric measurements of phase transformations in thin films of amorphous Te alloys used for optical data storage , 2003 .

[50]  Jaehyun Park,et al.  Maxima in the thermodynamic response and correlation functions of deeply supercooled water , 2017, Science.

[51]  C. Angell,et al.  Phase change alloy viscosities down to T g using Adam-Gibbs-equation fittings to excess entropy data: A fragile-to-strong transition , 2015 .

[52]  Ralf Busch,et al.  Structural evolution on medium-range-order during the fragile-strong transition in Ge15Te85 , 2017 .

[53]  Behrad Gholipour,et al.  Characterization of supercooled liquid Ge2Sb2Te5 and its crystallization by ultrafast-heating calorimetry. , 2012, Nature materials.

[54]  J. Liu.  Simple technique for measurements of pulsed Gaussian-beam spot sizes. , 1982, Optics letters.

[55]  Jan Siegel,et al.  Dynamics of ultrafast reversible phase transitions in GeSb films triggered by picosecond laser pulses , 1999 .

[56]  H. Philipp.  Optical Properties of Silicon Nitride , 1973 .

[57]  Daniel W. Hewak,et al.  Fragile‐to‐Strong Crossover in Supercooled Liquid Ag‐In‐Sb‐Te Studied by Ultrafast Calorimetry , 2015 .

[58]  Marcin Sikorski,et al.  Photon-in photon-out hard X-ray spectroscopy at the Linac Coherent Light Source , 2015, Journal of synchrotron radiation.

[59]  Matthias Wuttig,et al.  Calorimetric measurements of structural relaxation and glass transition temperatures in sputtered films of amorphous Te alloys used for phase change recording , 2007 .

[60]  Y. Sakaguchi,et al.  X-ray diffraction measurements for liquid As2Se3 up to the semiconductor-metal transition region , 1992 .

[61]  D. Herbert,et al.  Localized states in disordered systems , 1971 .

[62]  John Ziman,et al.  A theory of the electrical properties of liquid metals , 1965 .

[63]  Eric Pop,et al.  Low-Power Switching of Phase-Change Materials with Carbon Nanotube Electrodes , 2011, Science.

[64]  H. Saitoh,et al.  Semiconductor-Metal Transition Induced by the Structural Transition in Liquid Ge 15 Te 85 , 1993 .

[65]  Matthias Wuttig,et al.  Mechanical stresses upon crystallization in phase change materials , 2001 .

[66]  M. Stolpe,et al.  Breakdown of the Stokes-Einstein relation above the melting temperature in a liquid phase-change material , 2018, Science Advances.

[67]  J. Richard,et al.  Specific heat measurement of thin suspended SiN membrane from 8 K to 300 K using the 3ω-Völklein method. , 2013, The Review of scientific instruments.

[68]  Simone Raoux,et al.  Thermal conductivities and phase transition temperatures of various phase-change materials measured by the 3ω method , 2009 .

[69]  I. Kaban,et al.  Structural, electronic and kinetic properties of the phase-change material Ge2Sb2Te5 in the liquid state , 2016, Scientific Reports.

[70]  W. Matz,et al.  Investigation of the structure of molten Ge15Te85 in dependence on temperature , 1985 .

[71]  Matthias Wuttig,et al.  Aging mechanisms in amorphous phase-change materials , 2015, Nature Communications.

[72]  H.-S. Philip Wong,et al.  Phase Change Memory , 2010, Proceedings of the IEEE.

[73]  Siegfried Selberherr,et al.  Using six moments of Boltzmann’s transport equation for device simulation , 2001 .

[74]  W. J. Wang,et al.  Breaking the Speed Limits of Phase-Change Memory , 2012, Science.

[75]  A. Barnes,et al.  D4c: A very high precision diffractometer for disordered materials , 2002 .

[76]  J. Gaspard,et al.  Structure of covalently bonded materials: From the Peierls distortion to Phase-Change Materials , 2016 .

[77]  I. Kaban,et al.  Experimental and ab initio molecular dynamics study of the structure and physical properties of liquid GeTe , 2017 .

[78]  T. Araki,et al.  Spectroscopic observation of oxidation process in InN , 2004 .

[79]  Volker L. Deringer,et al.  A Quantum‐Mechanical Map for Bonding and Properties in Solids , 2018, Advanced materials.

[80]  Noboru Yamada,et al.  From local structure to nanosecond recrystallization dynamics in AgInSbTe phase-change materials. , 2011, Nature materials.

[81]  H. Eugene Stanley,et al.  Supercooled and glassy water , 2003 .