spintronic memories. magnetic domain wall motion memory magnetic race-track memory stuart parkin,...
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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 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
Selection criteria for new technology entries candidates
“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
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
Spin torque transfer MRAM
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
MRAM Scaling issue
0123456789
10
10 100 1000
L, nm
I, m
A
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
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
MTJ for spin-torque switching
MTJ is operated by spin polarized current passing through MTJ
NIc ~
~Nat
~L2
Scaling promise: spin-torque MRAM needs a smaller current for smaller dimensions
Injection efficiency
MRAM and ST-MRAM Scaling
Reciprocal Scaling Relations
MRAM and ST-MRAM Scaling
0.0001
0.001
0.01
0.1
1
10
100
1 10 100 1000
L, nm
I, m
A
electromagnetic WRITE
Spin-torque WRITE
Switching time vs. current
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
NIc ~
“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
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
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
Magnetic Domain Wall Motion memory
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
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
DWM at ~107 has been demonstrated
Domain wall velocity as a function of domain wall width
Benakli et al.,
JAP 103 (2008)
Seagate Group
Planar Configuration
W
t=5 nm
L
W, nm N, bitn, bit/cm2 R I V L, cm
P, W/cm2
J, A/cm2
100 2.0E+05 5.0E+09 4.0E+06 5.0E-03 20000 1 4.8E+06 1.0E+09
10 2.0E+06 5.0E+11 4.0E+07 5.0E-04 20000 1 3.3E+06 1.0E+09
12
~ W
LN
WLW
N
A
Nn
4~
W, nm N, bitn,
bit/cm2 R I V L, um P, W/cm2 J, A/cm2
100 2.10E+01 4.77E+09 4.00E+02 5.00E-03 2 1 4.76E+06 1.00E+09
10 2.01E+02 4.98E+11 4.00E+03 5.00E-04 2 1 3.33E+06 1.00E+09
W, cm N, bitn,
bit/cm2 R I V L, umP,
W/cm2 J, A/cm2
1.00E-05 2.10E+01 4.77E+09 4.00E+02 5.00E-05 0.02 1 476 1.00E+07
1.00E-06 2.01E+02 4.98E+11 4.00E+03 5.00E-06 0.02 1 333 1.00E+07
W, cm N, bitn,
bit/cm2 R I V L, cmP,
W/cm2 J, A/cm2
1.00E-05 2.10E+01 4.77E+09 4.00E+02 5.00E-06 0.00 1.00E-04 5 1.00E+06
1.00E-06 2.01E+02 4.98E+11 4.00E+03 5.00E-07 0.00 0.0001 3 1.00E+06
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
There is a considerable interest in DWM
IBM Samsung Hitachi Seagate Canon
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!