Introduction to Magnetic Random-Access Memory

Magnetic random-access memory (MRAM) is poised to replace traditional computer memory based on complementary metal-oxide semiconductors (CMOS). MRAM will surpass all other types of memory devices in terms of nonvolatility, low energy dissipation, fast switching speed, radiation hardness, and durability. Although toggle-MRAM is currently a commercial product, it is clear that future developments in MRAM will be based on spin-transfer torque, which makes use of electrons spin angular momentum instead of their charge. MRAM will require an amalgamation of magnetics and microelectronics technologies. However, researchers and developers in magnetics and in microelectronics attend different technical conferences, publish in different journals, use different tools, and have different backgrounds in condensed-matter physics, electrical engineering, and materials science. This book is an introduction to MRAM for microelectronics engineers written by specialists in magnetic materials and devices. It presents the basic phenomena involved in MRAM, the materials and film stacks being used, the basic principles of the various types of MRAM (toggle and spin-transfer torque; magnetized in-plane or perpendicular-to-plane), the back-end magnetic technology, and recent developments toward logic-in-memory architectures. It helps bridge the cultural gap between the microelectronics and magnetics communities.

Magnetic random-access memory (MRAM) is poised to replace traditional computer memory based on complementary metal-oxide semiconductors (CMOS). MRAM will surpass all other types of memory devices in terms of nonvolatility, low energy dissipation, fast switching speed, radiation hardness, and durability. Although toggle-MRAM is currently a commercial product, it is clear that future developments in MRAM will be based on spin-transfer torque, which makes use of electrons' spin angular momentum instead of their charge. MRAM will require an amalgamation of magnetics and microelectronics technologies. However, researchers and developers in magnetics and in microelectronics attend different technical conferences, publish in different journals, use different tools, and have different backgrounds in condensed-matter physics, electrical engineering, and materials science.This book is an introduction to MRAM for microelectronics engineers written by specialists in magnetic materials and devices. It presents the basic phenomena involved in MRAM, the materials and film stacks being used, the basic principles of the various types of MRAM (toggle and spin-transfer torque; magnetized in-plane or perpendicular-to-plane), the back-end magnetic technology, and recent developments toward logic-in-memory architectures. It helps bridge the cultural gap between the microelectronics and magnetics communities.

ABOUT THE EDITORS xiPREFACE xiiiCHAPTER 1 BASIC SPINTRONIC TRANSPORT PHENOMENA 1Nicolas Locatelli and Vincent Cros1.1 Giant Magnetoresistance 21.2 Tunneling Magnetoresistance 91.3 The Spin-Transfer Phenomenon 20CHAPTER 2 MAGNETIC PROPERTIES OF MATERIALS FOR MRAM 29Shinji Yuasa2.1 Magnetic Tunnel Junctions for MRAM 292.2 Magnetic Materials and Magnetic Properties 312.3 Basic Materials and Magnetotransport Properties 39CHAPTER 3 MICROMAGNETISM APPLIED TO MAGNETIC NANOSTRUCTURES 55Liliana D. Buda-Prejbeanu3.1 Micromagnetic Theory: From Basic Concepts Toward the Equations 553.2 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 73CHAPTER 4 MAGNETIZATION DYNAMICS 79William E. Bailey4.1 Landau-Lifshitz-Gilbert Equation 794.2 Small-Angle Magnetization Dynamics 844.3 Large-Angle Dynamics: Switching 904.4 Magnetization Switching by Spin-Transfer 95CHAPTER 5 MAGNETIC RANDOM-ACCESS MEMORY 101Bernard Dieny and I. Lucian Prejbeanu5.1 Introduction to Magnetic Random-Access Memory (MRAM) 1015.2 Storage Function: MRAM Retention 1045.3 Read Function 1105.4 Field-Written MRAM (FIMS-MRAM) 1125.5 Spin-Transfer Torque MRAM (STT-MRAM) 1185.6 Thermally-Assisted MRAM (TA-MRAM) 1355.7 Three-Terminal MRAM Devices 1505.8 Comparison of MRAM with Other Nonvolatile Memory Technologies 1535.9 Conclusion 157CHAPTER 6 MAGNETIC BACK-END TECHNOLOGY 165Michael C. Gaidis6.1 Magnetoresistive Random-Access Memory (MRAM) Basics 1656.2 MRAM Back-End-of-Line Structures 1666.3 MRAM Process Integration 1696.4 Process Characterization 187CHAPTER 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 1997.2 Nonvolatile Logic-in-Memory Architecture 2037.3 Circuit Scheme for Logic-in-Memory Architecture Based on Magnetic Flip-Flop Circuits 2097.4 Nonvolatile Full Adder Using MTJ Devices in Combination with MOS Transistors 2147.5 Content-Addressable Memory 2177.6 MTJ-based Nonvolatile Field-Programmable Gate Array 224APPENDIX 231INDEX 233