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Introduction to Spintronics: Modeling and Circuit Design Richard Dorrance Yuta Toriyama

EE201C: Winter 2012. Introduction to Spintronics: Modeling and Circuit Design Richard Dorrance Yuta Toriyama. Outline. Spintronics Primer What is it? Why should I care? How does it work? Magnetic Tunnel Junctions (MTJs) Modeling Statistical Variation Circuit Design with MTJs

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Introduction to Spintronics: Modeling and Circuit Design Richard Dorrance Yuta Toriyama

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  1. EE201C: Winter 2012 Introduction to Spintronics:Modeling and Circuit DesignRichard DorranceYuta Toriyama

  2. Outline • Spintronics Primer • What is it? • Why should I care? • How does it work? • Magnetic Tunnel Junctions (MTJs) • Modeling • Statistical Variation • Circuit Design with MTJs • Magnetic Random Access Memories • Magnetic Flip-Flops

  3. Spintronics? What’s that? • Electrons: • Mass • Charge • Velocity • Spin • Most modern electronics exploit charge • Spintronics exploits electron spin

  4. That’s Nice! But why should I care? • Spintronics has existed since the mid-1930s! • You use it every single day is these devices: • Hard Drives • Radiation Hardened Memories • Polarized LEDs • Next-Generation Devices • Spin-FETs • Universal Memories • Terahertz Lasers • Energy-Efficient LEDs

  5. Spintronic Operation • Spin Injector • Ferromagnetic layers tend to spin-polarize a current • Spin Detector • Ferromagnetic layers tend to scatter anti-parallel currents

  6. Spin Valves and Magnetic Tunnel Junctions Parallel Antiparallel • A Spin Valve combines a spin injector and a detector • Practical Spin Valve: Magnetic Tunnel Junction • Two ferromagnetic layers separated by a thin insulator

  7. MTJ Characteristics

  8. Current-Driven Excitation of Magnetic Multilayers J. C. Slonczewski J. Magn. Magn. Mater., 1996

  9. Landau–Lifshitz–Gilbert Equation Describes the precessionalmotion of magnetization in a solid

  10. Modified Landau–Lifshitz–Gilbert Equation

  11. A Statistical Study of Magnetic Tunnel Junctions for High-Density Spin Torque Transfer-MRAM R. Beach, et al. IEDM ’08, Dec. 2008

  12. TMR vs. RP Variation of RP and TMR approximately Gaussian

  13. Thermal Stability

  14. Write Bit Error Rate

  15. Write Threshold

  16. Read Disturbance

  17. Breakdown Voltages

  18. 2 Mb SPRAM with Bit-by-BitBi-Directional Current Write andParallelizing-Direction Current Read T. Kawahara, et al. ISSCC ‘07, Feb. 2007

  19. Spin-Transfer Torque Writing

  20. Spin-Transfer Torque Reading

  21. Selection of Read Direction

  22. Reducing Read Disturbance

  23. Reading with Reduced Bitline Voltages

  24. Chip Summary

  25. Magnetic Flip Flops forSpace Applications K.J. Hass, et al. IEEE Trans. Magn., Oct.2008

  26. Field Induced Magnetic Switching

  27. Writing: Current Steering Circuit

  28. Reading: Dual-MTJ Latch

  29. Recovery from a Cosmic Particle Strike

  30. References • J. C. Slonczewski, “Current-Driven Excitation of Magnetic Multilayers,” J. Magn. Magn. Mater., vol. 159, pp. L1 – L7, 1996. • R. Beach, et al., “A Statistical Study of Magnetic Tunnel Junctions for High-Density Spin Torque Transfer-MRAM (STT-MRAM),” IEDM 2008, pp. 1-4, Dec. 2008. • T. Kawahara, et al., “2 Mb SPRAM (SPin-Transfer Torque RAM) With Bit-by-Bit Bi-Directional Current Write and Parallelizing-Direction Current Read,” ISSCC’ 07, pp. 480-481, 617, Feb. 2007. • K.J. Hass, et al., “Magnetic Flip Flops for Space Applications,” IEEE Trans. Magn., vol. 42, no. 10, pp. 2751-2753, Oct. 2006.

  31. Questions?

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