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Spintronic Memories. Magnetic Domain Wall Motion memory Magnetic race-track memory Stuart Parkin, Magnetic race-track – a novel storage class spintronic.

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Presentation on theme: "Spintronic Memories. Magnetic Domain Wall Motion memory Magnetic race-track memory Stuart Parkin, Magnetic race-track – a novel storage class spintronic."— Presentation transcript:

1 Spintronic Memories

2 Magnetic Domain Wall Motion memory Magnetic race-track memory Stuart Parkin, Magnetic race-track – a novel storage class spintronic memory, Intern J. Mod. Physics B 22 (2008) 117 Spin torque transfer MRAM Should we consider storage-class memories in ERD? Does is belong to PIDS or to ERD? MRAM has been transferred from ERD to PIDS in 2003

3 Selection criteria for new technology entries candidates

4 Minimum Requirement Criteria The minimum requirements criteria for a new technology to be considered as a candidate for ERD chapter is sufficient research activity, e.g. the technology is explored by several research groups, or There is an extensive research activity of one group There are at least 2 publications in peer-reviewed journals

5 General Loose Criteria Potential for scaling Roadmap Driver On-chip integrated solutions Potential for embedded applications Outstanding research issues exist Guidelines for the research community and government funding agencies Not in production Innovation phase

6 Spin torque transfer MRAM

7 Conventional MRAM MRAM element is operated by magnetic field generated from current lines in the proximity of MTJ Wireless communication Proximity effects – crosstalk Scaling issue, Heat, reliability etc. FM free layer FM pinned layer

8 MRAM Scaling issue Scaling issue: Conventional MRAM needs a larger current for smaller dimensions T. Kawahara et al, 2Mb SPRAM (Spin- Transfer Torque RAM)…, IEEE J. Solid- State Circ. 43 (2008) 109 Hitachi group

9 Spin-torque switching Injected spin-polarized electrons interact with the magnetic moment of a free layer and transfer their angular momentum If sufficient current is applied, the exerted spin torque switches the free layer either parallel or anti-parallel to the pinned layer depending on the direction of flow of the current Attractive for memory array applications, does not have the magnetic half-select problem smaller switching current Spin torque transfer RAM (ST-RAM) MTJ for spin-torque switching

10 MTJ is operated by spin polarized current passing through MTJ ~N at ~L 2 Scaling promise: spin-torque MRAM needs a smaller current for smaller dimensions Injection efficiency

11 MRAM and ST-MRAM Scaling Reciprocal Scaling Relations

12 MRAM and ST-MRAM Scaling

13 Switching time vs. current

14 Outstanding research issues Theory: Critical current issue I c needs to be decreased From 10 7 A/cm 2 to 10 5 A/cm 2 New material structures MTJ current needs to be increased New MTJ design Injection efficiency Although the presence of spin torque has been unambiguously observed, its quantitative behavior in MTJ, especially its bias dependence has yet to be understood in detail J. C. Sankey et al., Nature Physics 4 (2008) 67 IBM group

15 New concepts are needed Nano-current-channel (NCC) injection FeSiO layer with columnar NCC structure Current can pass through NCC only Provide magnetic nucleation points and induce the free layer switching through the growth of the nucleation points

16 General Loose Criteria Discussion: Spin torque transfer MRAM Potential for scaling Roadmap Driver On-chip integrated solutions Potential for embedded applications Outstanding research issues exist Guidelines for the research community and government funding agencies Not in production Innovation phase Does is belong to PIDS or to ERD? MRAM has been transferred from ERD to PIDS in 2003

17 Magnetic Domain Wall Motion memory

18 Current-driven magnetic domain wall (DW) motion DWM DWM occurs in a submicron-size ferromagnetic stripe Charge carriers become polarized by the interaction between conduction electrons and local magnetic moments Exert torque on the magnetic moments within DW Sensed by TMR or GMR device

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21 Magnetic Race-track Memory A proposal for a novel storage-class memory, in which magnetic domains are used to store information in a magnetic race-track Shift register scheme A solid state memory with storage capacity same/better than HDD Improved performance and reliability The magnetic race track is comprised of tall columns of magnetic material arranged perpendicularly to the Si surface The domains are moved up and down by current pulses ~ns pulses Sensing by magnetic tunnel junction device

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25 DWM at ~10 7 has been demonstrated

26 Domain wall velocity as a function of domain wall width Benakli et al., JAP 103 (2008) Seagate Group

27 Planar Configuration W t=5 nm L W, nmN, bit n, bit/cm2RIVL, cm P, W/cm2 J, A/cm2 1002.0E+055.0E+094.0E+065.0E-032000014.8E+061.0E+09 102.0E+065.0E+114.0E+075.0E-042000013.3E+061.0E+09

28 W, nmN, bit n, bit/cm2RIVL, umP, W/cm2J, A/cm2 1002.10E+014.77E+094.00E+025.00E-03214.76E+061.00E+09 102.01E+024.98E+114.00E+035.00E-04213.33E+061.00E+09 W, cmN, bit n, bit/cm2RIVL, um P, W/cm2J, A/cm2 1.00E-052.10E+014.77E+094.00E+025.00E-050.0214761.00E+07 1.00E-062.01E+024.98E+114.00E+035.00E-060.0213331.00E+07 W, cmN, bit n, bit/cm2RIVL, cm P, W/cm2J, A/cm2 1.00E-052.10E+014.77E+094.00E+025.00E-060.001.00E-0451.00E+06 1.00E-062.01E+024.98E+114.00E+035.00E-070.000.000131.00E+06

29 Main Issue Due to the high current densities, strong heating occurs DW transformations have been shown to originate not only from spin torque effects but also from thermal excitations For applications, it is a key requirement to devise ways for efficient cooling

30 There is a considerable interest in DWM IBM Samsung Hitachi Seagate Canon

31 Outstanding research issues The capacity of spin-polarized current to move a domain wall was experimental established, but The mechanisms responsible for that motion remain under debate Current density needs to be decreased!


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