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

8. 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

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 for spin-torque switching
MTJ is operated by spin polarized current passing through MTJ
Injection efficiency W
~Nat
~L2
Scaling promise: spin-torque MRAM needs a smaller current for smaller dimensions

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
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) 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
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

17. Magnetic Domain Wall Motion memory

18. 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

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

25. DWM at ~107 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 t=5 nm W L W, nm N, bit n, 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
3.3E+06

28. W, cm
N, bit
n, bit/cm2 R I V
L, cm
P, 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
0.0001 3
W, cm
N, bit
n, bit/cm2 R I V
L, um
P, 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
333
W, nm
N, bit
n, 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
3.33E+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!