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!