Introduction to Magnetic Random-Access Memory

Bernard Dieny has conducted research in magnetism for 30 years. He played a key role in the pioneering work on spin-valves at IBM Almaden Research Center in 1990-1991. In 2001, he co-founded SPINTEC in Grenoble, France, a public research laboratory devoted to spin-electronic phenomena and components. Dieny is co-inventor of 70 patents and has co-authored more than 340 scientific publications. He received an outstanding achievement award from IBM in 1992 for the development of spin-valves, the European Descartes Prize for Research in 2006, and two Advanced Research Grants from the European Research Council in 2009 and 2015. He is co-founder of two companies, one dedicated to magnetic random-access memory, Crocus Technology, the other to the design of hybrid CMOS/magnetic circuits, EVADERIS. In 2011 he was elected Fellow of the Institute of Electrical and Electronics Engineers.Ronald B. Goldfarb was leader of the Magnetics Group at the National Institute of Standards and Technology in Boulder, Colorado, USA, from 2000 to 2015. He has published over 60 papers, book chapters, and encyclopedia articles in the areas of magnetic measurements, superconductor characterization, and instrumentation. In 2004 he was elected Fellow of the Institute of Electrical and Electronics Engineers (IEEE). From 1995 to 2004 he was editor in chief of IEEE Transactions on Magnetics. He is the founder and chief editor of IEEE Magnetics Letters, established in 2010. He received the IEEE Magnetics Society Distinguished Service Award in 2016.Kyung-Jin Lee is a professor in the Department of Materials Science and Engineering, and an adjunct professor of the KU-KIST Graduate School of Converging Science and Technology, at Korea University. Before joining the university, he worked for Samsung Advanced Institute of Technology in the areas of magnetic recording and magnetic random-access memory. His current research is focused on understanding the underlying physics of current-induced magnetic excitations and exploring new spintronic devices utilizing spin-transfer torque. He is co-inventor of 20 patents and has more than 100 scientific publications in the areas of magnetic random-access memory, spin-transfer torque, and spin-orbit torques. He received an outstanding patent award from the Korea Patent Office in 2005 and an award for Excellent Research on Basic Science from the Korean government in 2010. In 2013 he was recognized by the National Academy of Engineering of Korea as a leading scientist in spintronics, "one of the top 100 technologies of the future."

• About the Editors xiPreface A Perspective on Nonvolatile Magnetic Memory Technology xiiiChapter 1 Basic Spintronic Transport Phenomena 1Nicolas Locatelli and Vincent Cros1.1 Giant Magnetoresistance 21.1.1 Basics of Electronic Transport in Magnetic Materials 21.1.2 A Simple Model to Describe GMR: The “Two-Current Model” 51.1.3 Discovery of GMR and Early GMR Developments 71.1.4 Main Applications of GMR 81.2 Tunneling Magnetoresistance 91.2.1 Basics of Quantum Mechanical Tunneling 101.2.2 First Approach to Tunnel Magnetoresistance: Jullière’s Model 111.2.3 The Slonczewski Model 141.2.3.1 The Model 141.2.3.2 Experimental Observations 151.2.3.3 About the TMR Angular Dependence 151.2.4 More Complex Models: The Spin Filtering Effect 161.2.4.1 Incoherent Tunneling Through an Amorphous (Al2O3) Barrier 161.2.4.2 Coherent Tunneling Through a Crystalline MgO Barrier 171.2.5 Bias Dependence of Tunnel Magnetotransport 191.3 The Spin-Transfer Phenomenon 201.3.1 The Concept and Origin of the Spin-Transfer Effect 201.3.1.1 The “In-Plane” Torque 201.3.1.2 The “Out-of-Plane” Torque 231.3.2 Spin-Transfer-Induced Magnetization Dynamics 231.3.2.1 A Simple Analogy 241.3.2.2 Toward MRAM Based on Spin-Transfer Torque 251.3.3 Main Events Concerning Spin-Transfer Advances 26References 27Chapter 2 Magnetic Properties of Materials for Mram 29Shinji Yuasa2.1 Magnetic Tunnel Junctions for MRAM 292.2 Magnetic Materials and Magnetic Properties 312.2.1 Ferromagnet and Antiferromagnet 312.2.2 Demagnetizing Field and Shape Anisotropy 332.2.3 Magnetocrystalline Anisotropy, Interface Magnetic Anisotropy, and Perpendicular Magnetic Anisotropy 352.2.4 Exchange Bias 362.2.5 Interlayer Exchange Coupling and Synthetic Antiferromagnetic Structure 372.2.6 Spin-Valve Structure 382.3 Basic Materials and Magnetotransport Properties 392.3.1 Metallic Nonmagnetic Spacer for GMR Spin-Valve 392.3.2 Magnetic Tunnel Junction with Amorphous AlO Tunnel Barrier 412.3.3 Magnetic Tunnel Junction with Crystalline MgO(0 0 1) Tunnel Barrier 442.3.3.1 Epitaxial MTJ with a Single-Crystal MgO(0 0 1) Barrier 442.3.3.2 CoFeB/MgO/CoFeB MTJ with a (0 0 1)-Textured MgO Barrier for Device Applications 462.3.3.3 Device Applications of MgO-Based MTJs 48References 51Chapter 3 Micromagnetism Applied to Magnetic Nanostructures 55Liliana D. Buda-Prejbeanu3.1 Micromagnetic Theory: From Basic Concepts Toward the Equations 553.1.1 Free Energy of a Magnetic System 563.1.1.1 Exchange Energy 563.1.1.2 Magnetocrystalline Anisotropy Energy 573.1.1.3 Demagnetizing Energy 573.1.1.4 Zeeman Energy 603.1.2 Magnetically Stable State and Equilibrium Equations 613.1.3 Equations of Magnetization Motion 623.1.4 Length Scales in Micromagnetism 633.1.5 Modification Related to Spin-Transfer Torque Phenomena and Spin–Orbit Coupling 643.1.6 Thermal Fluctuations 653.1.7 Numerical Micromagnetism 663.2 Micromagnetic Configurations in Magnetic Circular Dots 673.3 STT-Induced Magnetization Switching: Comparison of Macrospin and Micromagnetism 703.4 Example of Magnetization Precessional STT Switching: Role of Dipolar Coupling 73References 76Chapter 4 Magnetization Dynamics 79William E. Bailey4.1 Landau–Lifshitz–Gilbert Equation 794.1.1 Introduction 794.1.2 Variables in the Equation 804.1.3 The Equation 814.1.3.1 Precessional Term 824.1.3.2 Relaxation Term 834.2 Small-Angle Magnetization Dynamics 844.2.1 LLG for Thin-Film, Magnetized in Plane, Small Angles 844.2.2 Ferromagnetic Resonance 854.2.3 Tabulated Materials Parameters 874.2.3.1 Bulk Values 874.2.3.2 Finite-Size Effects 884.2.4 Pulsed Magnetization Dynamics 894.3 Large-Angle Dynamics: Switching 904.3.1 Quasistatic Limit: Stoner–Wohlfarth Model 904.3.2 Thermally Activated Switching 934.3.3 Switching Trajectory 944.4 Magnetization Switching by Spin-Transfer 954.4.1 Additional Terms to the LLG 954.4.2 Full-Angle LLG with Spin-Torque 96Acknowledgments 97References 97Chapter 5 Magnetic Random-access Memory 101Bernard Dieny and I. Lucian Prejbeanu5.1 Introduction to Magnetic Random-Access Memory (MRAM) 1015.1.1 Historical Perspective 1015.1.2 Various Categories of MRAM 1025.2 Storage Function: MRAM Retention 1045.2.1 Key Role of the Thermal Stability Factor 1045.2.2 Thermal Stability Factor for In-Plane and Out-of-Plane Magnetized Storage Layer 1065.3 Read Function 1105.3.1 Principle of Read Operation 1105.3.2 STT-Induced Disturbance of the Storage Layer Magnetic State During Read 1115.4 Field-Written MRAM (FIMS-MRAM) 1125.4.1 Stoner–Wohlfarth MRAM 1125.4.2 Toggle MRAM 1155.4.2.1 Toggle Write Principle 1155.4.2.2 Improved Write Margin 1175.4.2.3 Applications of Toggle MRAM 1175.4.3 Limitation in Downsize Scalability 1185.5 Spin-Transfer Torque MRAM (STT-MRAM) 1185.5.1 Principle of STT Writing 1195.5.2 Considerations of Breakdown, Write, Read Voltage Distributions 1225.5.3 Influence of STT Write Pulse Duration 1235.5.4 In-Plane STT-MRAM 1245.5.4.1 Critical Current for Switching 1245.5.4.2 Minimization of Critical Current for Writing 1255.5.5 Out-of-Plane STT-MRAM 1285.5.5.1 Benefit of Out-of-Plane Configuration in Terms of Write Current 1305.5.5.2 Trade-off Between Strong Perpendicular Anisotropy and Low Gilbert Damping 1315.5.5.3 Benefit from Magnetic Metal/Oxide Perpendicular Anisotropy 1315.5.5.4 Downsize Scalability of Perpendicular STT-MRAM 1335.6 Thermally-Assisted MRAM (TA-MRAM) 1355.6.1 Trade-off Between Retention and Writability; General Idea of Thermally-Assisted Writing 1355.6.2 Self-Heating in MTJ Due to High-Density Tunneling Current 1365.6.3 In-Plane TA-MRAM 1365.6.3.1 Write Selectivity Due to a Combination of Heating and Field 1365.6.3.2 Reduced Power Consumption, Thanks to Low Write Field and Field Sharing 1385.6.4 TA-MRAM with Soft Reference: Magnetic Logic Unit (MLU) 1405.6.4.1 Principle of Reading with Soft Reference 1415.6.4.2 Content-Addressable Memory 1435.6.5 Thermally-Assisted STT-MRAM 1445.6.5.1 In-Plane STT Plus TA-MRAM 1445.6.5.2 Out-of-Plane STT Plus TA-MRAM 1455.7 Three-Terminal MRAM Devices 1505.7.1 Field versus Current-Induced Domain Wall Propagation 1505.7.2 Principle of Writing 1525.7.3 Advantages and Drawbacks of Three-Terminal Devices 1535.8 Comparison of MRAM with Other Nonvolatile Memory Technologies 1535.8.1 MRAM in the International Technology Roadmap for Semiconductors (ITRS) 1535.8.2 Comparison of MRAM and Redox-RAM 1555.8.3 Main Applications of MRAM 1555.9 Conclusion 157Acknowledgments 157References 158Chapter 6 Magnetic Back-end Technology 165Michael C. Gaidis6.1 Magnetoresistive Random-Access Memory (MRAM) Basics 1656.2 MRAM Back-End-of-Line Structures 1666.2.1 Field-MRAM 1666.2.2 Spin-Transfer Torque (STT) MRAM 1686.2.3 Other Magnetic Memory Device Structures 1696.3 MRAM Process Integration 1696.3.1 The Magnetic Tunnel Junction 1696.3.1.1 Substrate Preparation 1716.3.1.2 Film Deposition and Anneal 1726.3.1.3 Device Patterning 1746.3.1.4 Dielectric Encapsulation 1796.3.2 Wiring and Packaging 1836.3.2.1 Ferromagnetic Cladding 1846.3.2.2 Packaging 1866.3.3 Processing Cost Considerations 1866.4 Process Characterization 1876.4.1 200–300 mm Wafer Blanket Magnetic Films 1876.4.1.1 Current-in-Plane Tunneling (CIPT) 1886.4.1.2 Kerr Magnetometry 1896.4.2 Parametric Test of Integrated Magnetic Devices 1896.4.2.1 Magnetoresistance versus Resistance and Resistance versus Reciprocal Area 1906.4.2.2 Breakdown Voltage 1926.4.2.3 Device Spreads 194Acknowledgments 195References 195Chapter 7 Beyond Mram: Nonvolatile Logic-in-memory Vlsi 199Takahiro Hanyu, Tetsuo Endoh, Shoji Ikeda, Tadahiko Sugibayashi, Naoki Kasai, Daisuke Suzuki, Masanori Natsui, Hiroki Koike, and Hideo Ohno7.1 Introduction 1997.1.1 Memory Hierarchy of Electronic Systems 1997.1.2 Current Logic VLSI: The Challenge 2017.2 Nonvolatile Logic-in-Memory Architecture 2037.2.1 Nonvolatile Logic-in-Memory Architecture Using Magnetic Flip-Flops 2057.2.2 Nonvolatile Logic-in-Memory Architecture Using MTJ Devices in Combination with CMOS Circuits 2077.3 Circuit Scheme for Logic-in-Memory Architecture Based on Magnetic Flip-Flop Circuits 2097.3.1 Magnetic Flip-Flop Circuit 2097.3.2 M-Latch 2117.4 Nonvolatile Full Adder Using MTJ Devices in Combination with MOS Transistors 2147.5 Content-Addressable Memory 2177.5.1 Nonvolatile Content-Addressable Memory 2177.5.2 Nonvolatile Ternary CAM Using MTJ Devices in Combination with MOS Transistors 2207.6 MTJ-based Nonvolatile Field-Programmable Gate Array 224References 227Appendix Units for Magnetic Properties 231Index 233