Observation and modeling of polycrystalline grain formation in Ge2Sb2Te5

The relationship between the polycrystalline nature of phase change materials (such as Ge2Sb2Te5) and the intermediate resistance states of phase change memory (PCM) devices has not been widely studied. A full understanding of such states will require knowledge of how polycrystalline grains form, how they interact with each other at various temperatures, and how the differing electrical (and thermal) characteristics within the grains and at their boundaries combine through percolation to produce the externally observed electrical (and thermal) characteristics of a PCM device. We address the first of these tasks (and introduce a vehicle for the second) by studying the formation of fcc polycrystalline grains from the as-deposited amorphous state in undoped Ge2Sb2Te5. We perform ex situ transmission electron microscopy membrane experiments and then match these observations against numerical simulation. Ramped-anneal experiments show that the temperature ramp-rate strongly influences the median grain size. By...

[1]  Simone Raoux,et al.  Crystallization properties of ultrathin phase change films , 2008 .

[2]  V. Weidenhof,et al.  Structural transformations of Ge2Sb2Te5 films studied by electrical resistance measurements , 2000 .

[3]  A. Yelon,et al.  Interpretation and consequences of Meyer–Neldel rule for conductivity of phase change alloys , 2010 .

[4]  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 .

[5]  In situ X-ray diffraction study of crystallization process of GeSbTe thin films during heat treatment , 2005 .

[6]  Matthias Wuttig,et al.  Kinetics of crystal nucleation in undercooled droplets of Sb- and Te-based alloys used for phase change recording , 2005 .

[7]  E. Rimini,et al.  Amorphous-to-crystal transition of nitrogen- and oxygen-doped Ge2Sb2Te5 films studied by in situ resistance measurements , 2004 .

[8]  Jingsong Wei,et al.  Theoretical explanation of different crystallization processes between as-deposited and melt-quenched amorphous Ge2Sb2Te5 thin films , 2003 .

[9]  Martin Laurenzis,et al.  Electrical percolation characteristics of Ge2Sb2Te5 and Sn doped Ge2Sb2Te5 thin films during the amorphous to crystalline phase transition , 2005 .

[10]  Wei Zhang,et al.  In situ dynamic HR-TEM and EELS study on phase transitions of Ge2Sb2Te5 chalcogenides. , 2008, Ultramicroscopy.

[11]  A. Pirovano,et al.  Phase change mechanisms in Ge2Sb2Te5 , 2007 .

[12]  Andrea L. Lacaita,et al.  Unified mechanisms for structural relaxation and crystallization in phase-change memory devices , 2009 .

[13]  Yeonwoong Jung,et al.  Extremely low drift of resistance and threshold voltage in amorphous phase change nanowire devices , 2010 .

[14]  Mechanism of the isotermic amorphous-to-crystalline phase transition in Ge:Sb:Te ternary alloys , 2001 .

[15]  Nucleation, growth, and phase transformation mechanism of Ge2Sb2Te5 thin films , 2009 .

[16]  S. G. Bishop,et al.  Observation of the Role of Subcritical Nuclei in Crystallization of a Glassy Solid , 2009, Science.

[17]  D. Ielmini,et al.  Reliability Impact of Chalcogenide-Structure Relaxation in Phase-Change Memory (PCM) Cells—Part II: Physics-Based Modeling , 2009, IEEE Transactions on Electron Devices.

[18]  Kailash Gopalakrishnan,et al.  Overview of candidate device technologies for storage-class memory , 2008, IBM J. Res. Dev..

[19]  Daniele Ielmini,et al.  Statistics of Resistance Drift Due to Structural Relaxation in Phase-Change Memory Arrays , 2010, IEEE Transactions on Electron Devices.

[20]  Hideki Horii,et al.  A microscopic model for resistance drift in amorphous Ge2Sb2Te5 , 2011 .

[21]  Charlie Chung-Ping Chen,et al.  3-D Thermal-ADI: a linear-time chip level transient thermal simulator , 2002, IEEE Trans. Comput. Aided Des. Integr. Circuits Syst..

[22]  Matthias Wuttig,et al.  Atomic force microscopy study of laser induced phase transitions in Ge2Sb2Te5 , 1999 .

[23]  S. G. Bishop,et al.  Thermal conductivity of phase-change material Ge2Sb2Te5 , 2006 .

[24]  S. Lombardo,et al.  Amorphous to fcc-polycrystal transition in Ge2Sb2Te5 thin films studied by electrical measurements: Data analysis and comparison with direct microscopy observations , 2009 .

[25]  A. Petford-Long,et al.  Determination of the isothermal nucleation and growth parameters for the crystallization of thin Ge2Sb2Te5 films , 2002 .

[26]  A. Pirovano,et al.  Low-field amorphous state resistance and threshold voltage drift in chalcogenide materials , 2004, IEEE Transactions on Electron Devices.

[27]  Kinam Kim,et al.  Phase-Change Behavior of Stoichiometric Ge2Sb2Te5 in Phase-Change Random Access Memory , 2007 .

[28]  S. Lombardo,et al.  Amorphous-fcc transition in Ge2Sb2Te5 , 2010 .

[29]  Young-Kook Lee,et al.  Double electrical percolation phenomenon during the crystallization of an amorphous Ge2Sb2Te5 thin film under continuous heating , 2010 .

[30]  S. Braga,et al.  Dependence of resistance drift on the amorphous cap size in phase change memory arrays , 2009 .

[31]  Shih-Hung Chen,et al.  Phase-change random access memory: A scalable technology , 2008, IBM J. Res. Dev..

[32]  J. Hosson,et al.  Electron diffraction and high-resolution transmission electron microscopy of the high temperature crystal structures of Gexsb2Te3+x (x=1,2,3) phase change material , 2002 .

[33]  Myong R. Kim,et al.  Crystallization behavior of sputter-deposited amorphous Ge2Sb2Te5 thin films , 1999 .

[34]  R. Birringer,et al.  Estimating grain-size distributions in nanocrystalline materials from X-ray diffraction profile analysis , 1998 .

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

[36]  Matthias Wuttig,et al.  Phase change materials for non-volatile electronic memories , 2008 .

[37]  Kumar Virwani,et al.  Evidence of Crystallization–Induced Segregation in the Phase Change Material Te-Rich GST , 2011 .

[38]  K. Gopalakrishnan,et al.  Phase change memory technology , 2010, 1001.1164.

[39]  Young Kook Lee,et al.  Effect of Heating Rate on the Activation Energy for Crystallization of Amorphous Ge2Sb2Te5 Thin Film , 2009 .

[40]  Simone Raoux,et al.  Crystallization dynamics of nitrogen-doped Ge2Sb2Te5 , 2009 .

[41]  J. Douglas,et al.  A general formulation of alternating direction methods , 1964 .

[42]  C. Bongiorno,et al.  Crystallization of ion amorphized Ge2Sb2Te5 thin films in presence of cubic or hexagonal phase , 2010 .

[43]  D. Ielmini,et al.  Recovery and Drift Dynamics of Resistance and Threshold Voltages in Phase-Change Memories , 2007, IEEE Transactions on Electron Devices.

[44]  C. Wright,et al.  Models for phase-change of Ge2Sb2Te5 in optical and electrical memory devices , 2004 .

[45]  Winfried W. Wilcke,et al.  Storage-class memory: The next storage system technology , 2008, IBM J. Res. Dev..

[46]  Sang Chul Lee,et al.  Thermal conductivity anisotropy and grain structure in Ge2Sb2Te5 films , 2011 .

[47]  Xiaoqian Wei,et al.  Thickness Dependent Nano-Crystallization in Ge2Sb2Te5 Films and Its Effect on Devices , 2007 .

[48]  Grain Boundaries, Phase Impurities, and Anisotropic Thermal Conduction in Phase-Change Memory , 2011, IEEE Electron Device Letters.

[49]  S. Y. Kim,et al.  Investigation of crystallization behavior of sputter-deposited nitrogen-doped amorphous Ge2Sb2Te5 thin films , 2000 .

[50]  C. Wen,et al.  Crystal morphology and nucleation in thin films of amorphous Te alloys used for phase change recording , 2005 .

[51]  In situ transmission electron microscopy study of the crystallization of Ge2Sb2Te5 , 2004 .