Contents
1. History of Phase Change Memories…………………………………………………….1
Chung am
1.1 The Discovery of Phase Change Materials………………………………………1
1.2 Early Electronic Computers and Memory Systems …………………………..2
1.3 Pioneers in Phase Change Memory ………………………………………………..4
1.4 Early Attempts with Phase Change Memory……………………………………9
1.5 Rebirth of Phase Change Memory………………………………………………..10
References …………………………………………………14
Part I: Material Science: Theory and Experiment
2. Density Functional Theory Calculations
for Phase Change Materials………………………………………………………………17
Wojciech Wełnic
2.1 Introduction ………………………………………………………………………………17
2.2 The Theorem of Hohenberg and Kohn………………………………………….18
2.4 The Local Density Approximation ……………………………………………….22
2.5 Beyond Density Functional Theory………………………………………………23
2.6 Application of DFT in the Field of Phase Change Materials…………….24
2.6.1 Structure Determination……………………………………………………25
2.6.2 Electronic Properties………………………………………………………..29
References ………………………………………………………………………………………..36
3. Nature of Glasses ……………………………………………………………………………..39
Punit Boolchand, Matthieu Micoulaut, and Ping Chen
3.1 Introduction ………………………………………………………………………………39
3.2 Thermodynamics of the Glass Transition………………………………………41
3.3 Glass Transition from Dynamics ………………………………………………….43
3.4 Glass Forming Tendency…………………………………………………………….44
3.4.1 Compositional Trends of the Glass Transition Temperature ….46
3.5 Calorimetric Measurement of the Glass Transition
Temperature and Related Thermal Properties ………………………………..48
3.6 Three Generic Classifications of Glasses and Glass
Transitions ………………………………………………………………………………..51
3.7 Elastic Phases in Ionic and Super-ionic Glasses…………………………….. 54
3.8 Ideal Glasses and Self-organization of Networks…………………………… 54
3.9 Does the View Below the Glass Transition Temperature
Correlate with the View above the Glass Transition Temperature? ….. 56
3.10 Glass Formation in Hydrogen Bonded Networks…………………………… 57
3.11 Epilogue …………………………………………………………………………………..59
References ……………………………………………………………………………………….. 59
4. Structure of Amorphous Ge-Sb-Te Solids…………………………………………. 63
Stephen lliott
4.1 Introduction ………………………………………………………………………………63
4.2 Structural Order in Amorphous Materials …………………………………….. 64
4.2.1 Short-range Order ……………………………………………………………64
4.2.2 Medium-range Order ……………………………………………………….65
4.2.3 Long-range Structure……………………………………………………….66
4.3 Experimental Structural Probes…………………………………………………… 67
4.4 Structural Modeling……………………………………………………………………68
4.5 The Structure of Amorphous Phase-change Materials ……………………. 69
4.5.1 Experimental Studies………………………………………………………. 69
4.5.2 Simulational Studies ………………………………………………………..72
4.6 Summary ………………………………………………………………………………….78
References ………………………………………………………………………………………..79
5. Experimental Methods for Material Selection
in Phase-change Recording……………………………………………………………….81
Liesbeth van Pieterson
5.1 Introduction ………………………………………………………………………………81
5.2 Reversible Switching………………………………………………………………….82
5.3 Phase-change Materials ……………………………………………………………… 84
5.3.1 Crystallization by Nucleation and Growth …………………………. 86
5.3.2 Crystallization Dominated by Crystal Growth ……………………. 88
5.4 Archival Life Stability……………………………………………………………….. 89
5.5 Crystallization Rate …………………………………………………………………… 91
5.6 Material Optimization ……………………………………………………………….. 93
5.7 Outlook…………………………………………………………………………………….97
References ………………………………………………………………………………………..98
6. Scaling Properties of Phase Change Materials ………………………………… 99
Simone Raoux
6.1 Introduction ………………………………………………………………………………99
6.2 Thin Films of Phase Change Materials……………………………………….. 100
6.2.1 Crystallization Temperature as a Function of Film Thickness… 101
6.2.2 Crystallization Rate as a Function of Film Thickness ………… 105
6.2.3 Change in Optical Constants and Electrical and
Thermal Parameters as a Function of Film Thickness …………108
6.2.4 Limits of Storage Density in Thin Films …………………………..109
6.3 Phase Change Nanowires ………………………………………………………….111
6.4 Phase Change Nanoparticles ……………………………………………………..114
6.5 Scaling in Time – Switching Speed of Phase Change Materials ……..118
References. ……………………………………………………………………………………..120
7. Crystallization Kinetics…………………………………………………………………..125
Johannes A. Kalb
7.1 Theory ……………………………………………………………………………………125
7.1.1 Homogeneous Crystal Nucleation ……………………………………125
7.1.2 Heterogeneous Crystal Nucleation …………………………………..133
7.1.3 Crystal Growth………………………………………………………………135
7.2 Measurements………………………………………………………………………….138
7.2.1 Crystallization Parameters Around the Glass
Transition Temperature ………………………………………………….138
7.2.2 Crystallization Parameters Close to the Melting
Temperature………………………………………………………………….142
References ………………………………………………………………………………………145
8. Short and Long-Range Order in Phase Change Materials ………………..149
Paul Fons
8.1 Historical Background………………………………………………………………149
8.1.1 Glass Formation Process…………………………………………………150
8.2 Long-Range Order……………………………………………………………………151
8.2.1 GeTe ……………………………………………………………………………152
8.2.2 Ge-Sb-Te Alloys……………………………………………………………154
8.3 Short-Range Order……………………………………………………………………160
8.3.1 X-ray Absorption …………………………………………………………..160
8.3.2 Short Range Order in Sb-Te Alloys………………………………….170
References ………………………………………………………………………………………171
9. Optical and Electrical Properties of Phase Change Materials……………175
Bong-Sub Lee and Stephen G. Bishop
9.1 Introduction …………………………………………………………………………….175
9.2 Optical Constants and Optical Bandgap ………………………………………176
9.2.1 Determination of the Optical Constants and
Absorption Coefficient …………………………………………………..176
9.2.2 Optical Bandgap ……………………………………………………………179
9.2.3 Infrared Absorption: Band Tails and Free Carrier
Absorption ……………………………………………………………………181
9.2.4 Effects of Composition and Preparation Conditions……………182
9.3 Photo-induced Effects ……………………………………………………………… 184
9.3.1 Photo-induced Current and Optical Nonlinearity ………………. 184
9.3.2 Photo-Oxidation …………………………………………………………… 185
9.4 Conductivity and Phase Transformation …………………………………….. 186
9.4.1 Temperature-dependence of Resistivity …………………………… 186
9.4.2 Intermediate States: Percolation and Multilevel Recording … 187
9.4.3 Effects of Composition and Processing Conditions……………. 188
9.5 Electronic Transport Properties and Band Structure …………………….. 189
9.5.1 Characterization of Transport Properties………………………….. 189
9.5.2 Hexagonal Ge2Sb2Te5 ……………………………………………………. 191
9.5.3 Face-centered-cubic Ge2Sb2Te5 ………………………………………. 193
9.5.4 Amorphous Ge2Sb2Te5 ………………………………………………….. 194
9.6 Perspective for the Future…………………………………………………………. 194
References ………………………………………………………………………………………195
10. Development of Materials for Third Generation Optical
Storage Media ……………………………………………………………………………….199
Noboru Yamada
10.10 Materials for Blue Laser and Multi-layer Applications……………….. 219
10.11 Secrets of Present Phase-change Materials II…………………………….. 222
10.12 Conclusions………………………………………………………………………….. 223
References ……………………………………………………………………………………… 224
11. Novel Deposition Methods ……………………………………………………………… 227
Delia J. Milliron, Qiang Huang and Yu Zhu
11.1 Chemical Vapor Phase Deposition …………………………………………….. 227
11.2 Electrodeposition…………………………………………………………………….. 233
11. 3 Solution-phase Deposition …………………………………………………. 238
11.4 Nanomaterials…………………………………………………………………………. 241
11.5 Conclusions ……………………………………………………………………………. 243
References ………………………………………………………………………………………244
Part II: Applications: Optical, Solid State Memory
and Reconfigurable Logic
12. Optical Memory: From 1st to 3rd Generation and its Future……………251
Luping Shi
12.1 Introduction …………………………………………………………………………….251
12.2 Three Generations of Optical Media …………………………………………..252
12.2.1 The First Generation: Compact Discs (CDs) ……………………..253
12.2.2 The Second Generation: Digital Versatile Disks (DVDs) ……253
12 .2.3 The Third Generation: Blu-ray Discs (BDs)………………………256
12.3 The Basic Principle of Optical Recording ……………………………………257
12.4 Phase-change Optical Recording and Related Technologies…………..260
12.4.1 Phase-Change Optical Storage…………………………………………260
12.4.2 Techniques for Phase-Change Optical Storage…………………..270
12.5 The Future of Optical Storage ……………………………………………………279
References ………………………………………………………………………………………282
13.
Junji Tominaga
13.1 Introduction …………………………………………………………………………….285
13.2 Diffraction Limit and Near-Field Optics ……………………………………..286
13.3 Small Aperture and Non-propagating Photons……………………………..288
13.4 Super-resolution Near-field Structure (Super-RENS)
Principle to Retrieve Non-propagating Light ……………………………….290
13.5 Origin of the Strong Scattered Signals for 4th Generation
Super-RENS Disks …………………………………………………………………..292
13.6 Beyond Super-RENS………………………………………………………………..296
References ………………………………………………………………………………………297
14. Phase Change Memory Device Modeling …………………………………………299
Daniele Ielmini
14.1 Introduction …………………………………………………………………………….299
14.2 Device Operation……………………………………………………………………..300
14.3 Modeling of Electrical Conduction in the Amorphous Phase………….302
14.4 Threshold Switching in the Amorphous Chalcogenide ………………….306
14.5 Modeling the Electrical Conduction in the Crystalline
Chalcogenide …………………………………………………………………………..308
14.6 Electro-thermal Modeling of the Programming Characteristics ………309
14.7 Modeling the Amorphous to Crystalline Phase Transformation ……..314
14.8 Modeling the Structural Relaxation in the Amorphous Phase…………320
14.9 Summary and Outlook………………………………………………………………325
References ………………………………………………………………………………………327
15. Phase Change Random Access Memory Advanced
Prototype Devices and Scaling ……………………………………………………….. 331
Yi-Chou Chen
15.1 Introduction ……………………………………………………………………………. 331
15.2 Device Scaling by Reducing the Electrode Contact Area ……………… 332
15.2.1 The Heater Structure……………………………………………………… 333
15.2.2 The Edge Contact Structure……………………………………………. 337
15 .2.3 μTrench Structure…………………………………………………………. 338
15.2.4 The Ring Structure………………………………………………………… 338
15.3 Device Scaling by Reducing the Phase Change Material Volume …..339
15.3.1 The Pillar Structure……………………………………………………….. 340
15.3.2 The Line Structure………………………………………………………… 341
15.3.3 The Bridge Structure …………………………………………………….. 342
15.4 Other Prototype Devices…………………………………………………………… 343
15.4.1 Scaling Both the Material and the Contact ……………………….. 344
15.4.2 Multi-level Cell ……………………………………………………………. 345
15.4.3 Confined Structure…………………………………………………………345
15.5 Advanced Device Testing…………………………………………………………. 347
15.6 Summary ………………………………………………………………………………..349
References ………………………………………………………………………………………350
16. Phase Change Memory Cell Concepts and Designs …………………………. 355
Roberto Bez, Robert J. Gleixner, Fabio Pellizzer,
Agostino Pirovano and Greg Atwood
16.1 Introduction ……………………………………………………………………………. 355
16.2 Technology Overview ……………………………………………………………… 356
16.3 Phase Change Memory Cell Electrical Characterization……………….. 361
16.4 Phase Change Memory Cell Reliability ……………………………………… 368
16.4.1 Data Retention Characterization……………………………………… 369
16.4.2 Retention Behavior with Device Scaling………………………….. 376
16.4.3 Cycling Endurance ……………………………………………………….. 377
16.5 Summary and Outlook……………………………………………………………… 378
References ………………………………………………………………………………………379
17. Phase Change Random Access Memory Integration ……………………….. 381
Matthew J. Breitwisch
17.1 Introduction ……………………………………………………………………………. 381
17.2 Phase Change Random Access Memory Design Basics ……………….. 382
17.3 Review of Desired Phase Change Memory Cell Characteristics…….. 386
17.4 The Access Device …………………………………………………………………..390
17.5 Device Design Considerations ………………………………………………….. 393
17.5.1 The Mushroom Cell without or with Bottom
Ring Electrode ………………………………………………………………393
17.5.2 The Pillar Cell………………………………………………………………. 397
17 .5.3 The μ ll…………………………………………………………..399
17.5.4 The Pore Cell ………………………………………………………………..399
17.6 Multi-Level Phase Change Random Access Memory ……………………403
17.7 Concluding Remarks ………………………………………………………………..406
References ………………………………………………………………………………………406
18. Reconfigurable Logic ……………………………………………………………………..409
James Lyke
18.1 Introduction …………………………………………………………………………….409
18.2 Digital System Basics……………………………………………………………….410
18.3 Simple Configurable Digital Systems …………………………………………414
18.4 Considerations in Computation Architectures………………………………419
18.5 Multi-valued Systems ……………………………………………………………….420
18.6 Threshold Logic……………………………………………………………………….422
18.7 Artificial Neural Networks ………………………………………………………..425
18.8 Other Analog-domain Programmable Systems …………………………….426
18.9 Conclusions …………………………………………………………………………….429
References ………………………………………………………………………………………429
Author Bios ………………………………………………………..431
Index ………………………………………………………………….437