Spintronic Memories

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Spintronic Memories
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• 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
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Selection criteria for new technology entries
candidates
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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

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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

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Spin torque transfer MRAM
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Conventional MRAM
MRAM element is operated by magnetic field
generated from current lines in the proximity of
MTJ
FM free layer
FM pinned layer
Wireless communication Proximity effects
crosstalk Scaling issue, Heat, reliability etc.
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MRAM Scaling issue
T. Kawahara et al, 2Mb SPRAM (Spin-Transfer
Torque RAM), IEEE J. Solid-State Circ. 43
(2008) 109 Hitachi group
Scaling issue Conventional MRAM needs a larger
current for smaller dimensions
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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

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MTJ for spin-torque switching
MTJ is operated by spin polarized current passing
through MTJ
Injection efficiency
Nat
L2
Scaling promise spin-torque MRAM needs a smaller
current for smaller dimensions
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MRAM and ST-MRAM Scaling
Reciprocal Scaling Relations
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MRAM and ST-MRAM Scaling
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Switching time vs. current
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Outstanding research issues

• Theory
• Critical current issue
• Ic needs to be decreased
• From 107 A/cm2 to 105 A/cm2
• 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
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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

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General Loose Criteria Discussion Spin torque
transfer MRAM
Does is belong to PIDS or to ERD? MRAM has been
transferred from ERD to PIDS in 2003

• 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

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Magnetic Domain Wall Motion memory
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Magnetic Domain Wall Motion memory

• 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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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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DWM at 107 has been demonstrated
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Domain wall velocity as a function of domain wall
width
Benakli et al., JAP 103 (2008) Seagate Group
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Planar Configuration
t5 nm
W
L
W, nm N, bit n, bit/cm2 R I V L, cm P, W/cm2 J, A/cm2
100 2.0E05 5.0E09 4.0E06 5.0E-03 20000 1 4.8E06 1.0E09
10 2.0E06 5.0E11 4.0E07 5.0E-04 20000 1 3.3E06 1.0E09
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W, nm N, bit n, bit/cm2 R I V L, um P, W/cm2 J, A/cm2
100 2.10E01 4.77E09 4.00E02 5.00E-03 2 1 4.76E06 1.00E09
10 2.01E02 4.98E11 4.00E03 5.00E-04 2 1 3.33E06 1.00E09
W, cm N, bit n, bit/cm2 R I V L, um P, W/cm2 J, A/cm2
1.00E-05 2.10E01 4.77E09 4.00E02 5.00E-05 0.02 1 476 1.00E07
1.00E-06 2.01E02 4.98E11 4.00E03 5.00E-06 0.02 1 333 1.00E07
W, cm N, bit n, bit/cm2 R I V L, cm P, W/cm2 J, A/cm2
1.00E-05 2.10E01 4.77E09 4.00E02 5.00E-06 0.00 1.00E-04 5 1.00E06
1.00E-06 2.01E02 4.98E11 4.00E03 5.00E-07 0.00 0.0001 3 1.00E06
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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

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There is a considerable interest in DWM

• IBM
• Samsung
• Hitachi
• Seagate
• Canon

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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!