Ultrafast Switching in Magnetic Tunnel Junction based Orthogonal Spin Transfer Devices

1. Ultrafast Switching in Magnetic Tunnel Junction basedOrthogonal 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] SingulusTechnologies AG, 63796 Kahl am Main, Germany *: presenter Appl. Phys. Lett. 97, 242510 (2010) Match Meeting 2011, Dallas TX

2. Outline • Sample • Design • To obtain fast switching • Why orthogonal geometry + MTJ? • Sample • Characteristic • Sample structure • Coercive field and energy barrier • Switching • Measurement • Fast switching • Unique behavior Match Meeting 2011, Dallas TX

3. Switching in collinear devices • Initially: • No spin torque, if no thermal fluctuation • Waiting for large thermal fluctuation • Incubation delay (~ns) • Unpredictable switching process • During the switching process: • In – plane: complicated trajectory • Perpendicular: fastest motion(precession) doesn’t contribute to switching m mp Polarizing layer electron Switchable layer Match Meeting 2011, Dallas TX

4. -Bdemag Switching in orthogonal devices A.D. Kent, APL(2004) t=T/2 t=T t=0 • Merits: • Large initial torque. • Deterministic dynamics. • Fast switching. • Low power consumption. Current B • Differences from collinear: • Bi – polar switching. • Non – monotonic switching probability distributions Match Meeting 2011, Dallas TX

5. Sample structure SAF: PtMn CoFe Ru (AF coupled) CoFeB Barrier: MgO Free layer: CoFeB (3 nm) Space: Cu Polarizer: CoNi/CoPd Size: 40 nm x 80 nm ~ 80 nm x 240 nm Shape: rectangles, ellipses and hexagons. Match Meeting 2011, Dallas TX

6. Hysteresis Match Meeting 2011, Dallas TX

7. Energy barrier Match Meeting 2011, Dallas TX

8. Magnetic field Fast switching measurements Switching only happen during the current pulse 1 2 Current Pulse Measure R Measure R’ 3 Compare R, R’ not switch 2 switched 3 2 1 Apply the same pulse 100 – 10,000 times Match Meeting 2011, Dallas TX

9. Fast switching • 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 Match Meeting 2011, Dallas TX

10. Bi–polar and non–monotonic • Bi – polar switching: • Appears for both P-> AP and AP-> P switching • The torque originates from the perpendicular polarizer • Heating is not the main mechanism since SP is different for different polarities • Non – monotonic switching: • Clearly appears in P -> AP switching with Vp > 0 and AP -> P switching with Vp< 0 • Qualitatively consistent with the deterministic switching Match Meeting 2011, Dallas TX

11. Summary • We have fabricated OST-MRAM devices that incorporate a magnetic tunnel junction. • 100% switching probability is reached for pulses shorter than 500 ps requiring an energy < 450 fJ. • Due to the perpendicular polarizer switching is possible for both pulse polarities. • Precessionalswitching has been observed in the non-monotonicbehavior of the switching probability versus pulse amplitude. Match Meeting 2011, Dallas TX

12. Thank you ! Match Meeting 2011, Dallas TX

13. Material hysteresis Match Meeting 2011, Dallas TX

14. Spin Torque • Spin torque – the amount of transverse angular momentum transferred in unit time. e mp electron m magnetization Match Meeting 2011, Dallas TX

15. Spin Transfer Devices Memory 1 Memory 2 Oscillator / Memory Kent et al., APL (2004) Ebelset al., Nat. Mat (2007) Lee et al., APL (2009) Papusoi et al., APL(2009) Beaujour et al., SPIE(2009) Mangin et al., Nat. Mat. (2006) Mangin et al., APL (2009) Sun, PRB (2000) Bedau et al., APL (2010) Match Meeting 2011, Dallas TX