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Compact Modeling of MTJs for use in STT-MRAM

Progress Update. Compact Modeling of MTJs for use in STT-MRAM. Richard Dorrance Advisor: Prof. Dejan Marković March 12, 2010. Motivation. Magnetic Tunnel Junctions (MTJs) exhibit magnetic hysteresis Excellent potential as memory Integratable with CMOS Non-volatile

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Compact Modeling of MTJs for use in STT-MRAM

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  1. Progress Update Compact Modeling of MTJs for use in STT-MRAM Richard DorranceAdvisor: Prof. Dejan Marković March 12, 2010

  2. Motivation • Magnetic Tunnel Junctions (MTJs)exhibit magnetic hysteresis • Excellent potential as memory • Integratable with CMOS • Non-volatile • Spin-Transfer-Torque (STT) is a recently discovered phenomena • Predicted in 1996, observed in 2000 • No good compact model currently exists • Existing models oversimplify and ignore critical nonlinearities (temperature and voltage) • Problem for simulating STT-MRAM

  3. STT-MRAM

  4. Basic MTJ Structure

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

  6. Compact Model Landau–Lifshitz–Gilbert Equation Julliere’s Conductance Model

  7. Temperature Nonlinearities • Saturation Magnetization • Weiss theory of ferromagnetism • Spin-Polarization • Affects resistance and STT • Modeled by:

  8. Voltage Nonlinearities • TMR changes for an applied bias voltage • Simple fitting function

  9. Simulation Setup • Compare transient behavior of MTJ model with a commercially available Micromagnetic Simulator: • ±1 mA, 10 ns pulses (30 ns total) • Total simulation time: • Micromagnetic Simulator: 13.5 hours • Verilog-A Model: 0.750 seconds

  10. Simulation Results b(θ) not implemented

  11. Future Work • Validation/refinement of model to measured devices • Explore the use of fitted function to replace b(θ) • b(θ) currently model a simple 5-layer structure • MTJ have 20+ layers with synthetic ferromagnets • Model C-STT 3rd Magnetic Layer (Perpendicular) • easier to switch • switching has greater thermal independence

  12. References [1] J. C. Slonczewski, J. Magn. Magn. Mater., vol. 159, pp. L1 – L7, 1996. [2] A. Raghunathan, et al., Magnetics, IEEE Trans., vol. 45, pp. 3954–3957, Oct. 2009. [3] C. H. Shang, et al., Phys. Rev. B, vol. 58, pp. R2917–R2920, Aug 1998. [4] Y. Lu, et al., J. Appl. Phys. vol. 83, no. 11. AIP, 1998, pp. 6515–6517. [5] X. Kou, et al., Applied Physics Letters, vol. 88, no. 21, p. 212115, 2006. [6] P. Wiśniowski, et al., Physica Status Solidi, vol. 201, pp. 1648–1652, 2004. [7] P. Padhan, et al., Applied Physics Letters, vol. 90, no. 14, p. 142105, 2007.

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