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H. Liu [1]* , D. Bedau [1] , D. Backes [1] ,

Statistical and Time Resolved Studies of Switching in Magnetic Tunnel Junction based Orthogonal Spin Transfer Devices. H. Liu [1]* , D. Bedau [1] , D. Backes [1] , J. A. Katine [2] , J. Langer [3] , and A. D. Kent [1] [1] Department of Physics, New York University, New York, NY 10003 USA

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H. Liu [1]* , D. Bedau [1] , D. Backes [1] ,

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  1. Statistical and Time Resolved Studies of Switching in Magnetic Tunnel Junction based Orthogonal Spin Transfer Devices H. Liu[1]*, D. Bedau[1], D. Backes[1], J. A. Katine[2], J. Langer[3], and A. D. Kent[1] [1] Department of Physics, New York University, New York, NY 10003 USA [2] San Jose Research Center, Hitachi-GST, San Jose, California 95135 USA [3] Singulus Technologies AG, 63796 Kahl am Main, Germany *: presenter Appl. Phys. Lett. 97, 242510 (2010) March Meeting 2012, Boston Massachusetts

  2. Outline • Sample • Design • Goal: fast, reliable switching • Why orthogonal geometry? • Fast • Switching • Sample characterization • Fast switching & low energy cost • Real-time • Measurement • Most transition within 200 ps • Possible precessional switching March Meeting 2012, Boston Massachusetts

  3. Switching in collinear devices • No initial spin torque, if no thermal fluctuation. • Waiting for large thermal fluctuation. • Incubation delay (~ ns). • Unpredictable switching process. m mp Polarizing layer electron Switchable layer March Meeting 2012, Boston Massachusetts

  4. Switching in orthogonal devices A.D. Kent et al., Appl. Phys. Lett. 84, 3897(2004) -Bdemag t=T/2 t=T • Merits: • Large initial torque. • Fast switching process. • Deterministic switching. • Low power consumption. t=0 Current • Differences from collinear: • Bipolar switching. • Precessional switching. March Meeting 2012, Boston Massachusetts

  5. Sample structure Appl. Phys. Lett. 97, 242510 (2010) SAF: PtMn CoFe Ru (AF coupled) CoFeB Barrier: MgO Free layer: CoFeB (3 nm) Spacer: Cu Polarizer: CoNi/CoPd March Meeting 2012, Boston Massachusetts

  6. Typical hysteresis TMR 100 %, RA~ 5 Ωμm2 . Size: 40 nm x 80 nm ~ 105 nm x 240 nm. Shape: rectangles, ellipses and hexagons. Characterized: tens of thousands of samples. March Meeting 2012, Boston Massachusetts

  7. Magnetic field Fast switching measurements Switching only happens during the current pulse 1 2 Current Pulse Measure R Measure R’ 3 Compare R, R’ not switch 2 switched 3 Apply the same pulse 100 – 10,000 times 1 2 March Meeting 2012, Boston Massachusetts

  8. Previous Results 60 x 180 nm2, Hexagon MR = 107%, Rp = 400 Ω Hc = 14 mT • Fast switching • 100 % under 500 ps • No nano-seconds incubation delay • Low energy cost • -0.6 V, 500 ps • 400 Ω < R < 800 Ω • 225 fJ < E < 450 fJ Appl. Phys. Lett. 97, 242510 (2010) March Meeting 2012, Boston Massachusetts

  9. Bi-polar switching P->AP Switching e- e- 50 x 100 nm2, Rect. MR = 112%, Rp = 2.2 kΩ Hc = 8 mT Negative voltage favors the P state according to the STT of the RL Positive voltage favors the AP state according to the STT of the RL March Meeting 2012, Boston Massachusetts

  10. Real-time measurements e- AP P start switch March Meeting 2012, Boston Massachusetts

  11. Precessional switching P AP AP AP P P P Precess and switch to AP state Precess and remain in P state March Meeting 2012, Boston Massachusetts

  12. Conclusion • Fabricated OST-MRAM devices that incorporate magnetic tunnel junctions. • Achieved high TMR (>100%) with low RA~ 5 W mm2 and perpendicular polarizer with excellent characteristics: high spin-polarization and large perpendicular magnetic anisotropy. • Demonstrated 100% switching probability in thermally stable elements with 500 ps duration pulses (0.7 V), requiring just 450 fJ. • Can time-resolve individual switching events showing fast and precessional switching. Appl. Phys. Lett. 97, 242510 (2010) March Meeting 2012, Boston Massachusetts

  13. Thank you ! March Meeting 2012, Boston Massachusetts

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