Collection of Selected Presentation Materials from Recent Talks

Spintronic Devices for Nonvolatile VLSIs
Hideo Ohno
Center for Spintronics Integrated Systems, Tohoku University
Laboratory for Nanoelectronics and Spintronics, Research Institute of ElectricalCommunication, Tohoku University
WPI-Advanced Institute for Materials Research, Tohoku University
Center for Innovative Integrated Electronic Systems, Tohoku University
Collaborators: T. Endoh, T. Hanyu, H. Sato, S. Fukami, S. Kanai, S. Ikeda, F. Matsukura and the CSIS teamWork supported by the FIRST Program from JSPSand partly by R & D for Next-Generation Information Technology of MEXT

http://www.csis.tohoku.ac.jp/1Outline

1.
2.
3.
4.
5.

Introduction
Magnetic Tunnel Junction (MTJ)
Electrical Switching of MTJ
Three-terminal Domain Wall Device
SummaryChallenges VLSI Technology FaceMPU Power Consumption（W）

PowerConsumption

Interconnection
Delay
Interconnect wiring

Active power

Logic

MemorySignal bottleneck

Standby powerby leakage current

YearLogic

MemoryLeakageCurrent

Nonvolatile working memory is in needFeatures of non-volatilefor memory device

FlashFRAM

SpinDevice

Access Speed
Non destructive Read
Write Endurance
Scalability
Operation Voltage△○×○△△○○○

○×△△

○
○

System (Memory) Hierarchy
Nonvolatile
Logic-in-Memory

current

near futurefuture

Magnetic tunnel junction based memory elements to counter dynamic andstatic power, and interconnection delay
H. Ohno et al., IEDM 2010 (invited)Non-volatile CMOS VLSIs with spintronics

600MHzNonvolatile TCAM
1Mb Array Three
MTJ/CMOS Latch(Most compact TCAM Terminal DW Cell
(Fastest nonvolatile latch)cell, 4T-2MTJ)(High endurance)(IEDM 2011）（VLSI 2011）(VLSI 2012)

First Auto Design
Tool forSpintronics CMOS
(2011）

Nonvolatile GPU(Largest ScaleSpintronics Random
Logic 500kgate/chip)（ISSCC 2013）

Nonvolatile
microcomputer(First nonvolatile
microcomputer)（ISSCC 2014）

Nonvolatile FPGAwith TSV(First 3D Spintronics
CMOS Processor)（VLSI 2012）

1.5nsec / 1Mbit
Embedded MRAM
(Fastest nonvolatile
1Mbit memory)（VLSI 2013）

On 300 mm wafers

Magnetic Tunnel Junctions (MTJs)

Domain Wall

two terminal

three terminal

Nonvolatile, fast, low voltage and high endurance

Switching Current Ic0 and Energy Barrier ∆=E/kBT
perpendicular

1
E =
M S H K  V K eff V22αγ e
IC 0 =K eff V )(µB g∝αE

Perpendicular MgO-CoFeB MTJ
JC0 = 3.8 MA/cm2(IC0 = 48 μA)
E/kBT ~ 40
TMR ratio = 110%
Ta = 350oC

40 nm

(b)
(a)

Top electrode
Cr/Au
Ru
Ta

interface perpendicularanisotropy

CoFeB
MgO
CoFeB

Ta(c)
Ru
Ta
SiO2/Si sub.

Bottom electrode

5 nm

S. Ikeda et al., Nature Mat. 9, 721 (2010)

Size dependence of IC0
Recording layer volume, Vrec (nm3)

Critical current, IC0 (µA)

20001000

2000150

IC0 (P to AP)IC0 (AP to P)

10044 nm

3000

4000

5000

76 nm
Junction size 70 nm
59 nm
53 nm

500-50-10001000

2000

3000

4000

5000

Recording layer area, Srec (nm2)
H. Sato et al. Appl. Phys. Lett. 99, 042501 (2011)

Size dependence of ∆=E/kBT
Recording volume, Vrec (nm3)

Thermal stability factor, E/kBT

8001000

2000

3000

4000

5000

Junction size
59 nm
53 nm
44 nm

6070 nm 76 nm

E ≠ KV40

200pulse current
pulse field
previous result
01000

2000

3000

4000

5000

Recording layer area, Srec (nm2)
H. Sato et al., Appl. Phys. Lett. 99, 042501 (2011).

Nucleation diameter
NucleationembryoDn (nm)DnK eff ( Dn / 2 ) t
2∆=6040

Dn ~ 40 nm

2000 10 20 30 40 50 60 70 80 90 100

Junction diameter (nm)k BTAS δW = π
Our results along with others suggest Dn ≈K eff
H. Sato et al., Appl. Phys. Lett. 99, 042501 (2011).

E and layer thickness
E K=K eff π ( Dn / 2 ) t=eff V
2E ≈ K eff π (δ W / 2 ) t
2=π AS t
34∝t

H. Sato et al., IEEE Magn. Lett. 3, 3000204 (2012).

M S2 Ki
 K eff = + K b −t2µ0 

CoFeB thickness dependence of E/kBT80

•

E/kBT

60

tCoFeB* (= trec) was determined bysubtracting magnetically dead layer(0.4 nm) at CoFeB/Ta interface.

40

E ≈ K eff π (δ w / 2) 2 t rec

20= π 3 As t rec / 400.0

0.5

1.0

tCoFeB* (nm)1.52.0• A linear relationship between E/kBT and trec
• The slope of 36 nm-1 ⇒ As* ≈ 19 pJ/m
H. Sato et al., IEEE Magn. Lett. 3, 3000204 (2012).

Domain patterns of CoFeB
Magneto-optical Kerr effect (MOKE) images after demagnetization
sample A (t = 1.1 nm), as-deposited

50 µm

10 K

100 K

200 K

300 K

200 K

300 K

sample B (t = 1.3 nm), annealed at 350oC

50 µm

10 K

100 K

T ≥ 100 K• Domain walls moved smoothly• Labyrinth patterns were formed

T ≤ 50 K• Domain walls were strongly pinned• Complex patterns were formed
M. Yamanouchi et al., IEEE Magn. Lett. 2, 3000304 (2011).

Domain patterns of CoFeB

As (pJ/m) at 300 K

δw (nm) at 300 K

sample A (t = 1.1 nm, As-deposited)

8.4

43

sample B (t = 1.3 nm, 350oC)

3167

M. Yamanouchi et al, IEEE Magn. Lett., 2, 300304 (2011)

Double interface structure

SingleTa(5)/Ru(5)CoFeB(1.6)
MgO
CoFeB(0.9)
Ta(5)/Ru(10)/Ta(5)Si/SiO2 sub.
(70 nmφ)E/kBTJC0 (MA/cm2)

Referencelayer

DoubleTa(5)/Ru(5)MgO
CoFeB(1.0)
Ta(0.4)
CoFeB(1.6)
MgO
CoFeB(0.9)
Ta(5)/Ru(10)/Ta(5)Si/SiO2 sub.

Single51
3.3

Double95
3.2

Recordinglayer

H. Sato, et al., Appl. Phys. Lett. 101, 022414 (2012).

Double MgO
Double-MgO MTJ (DMTJ)
annealed at Ta = 350 oC
Ru

CoFe

Ta

Ru

MnIr

CoFe(B)

CoFe
Ru

MgO

CoFe(B)MgO

CoFe(B)

MnIr(a) Co(b) Fe(c) B

CoFe
Ru
CoFe(B)

(ii)

MgO

MgO

CoFe(B)

CoFe(B)
Ru
CoFe

(iii)
(i)

CoFe(B)
MgO

MnIr

MgO

NiFe
Ta
CoFe(B)
RuTa

EELS element map

10 nm

Ru

5 nm

CoFe(B)
Ru
CoFe
MnIr

10 nm

CoFe

350

SMTJ

TMR ratio (%)

300250200

DMTJ

150100500250

H. D. Gan et al., Appl. Phys. Lett. 96 (2010) 192507.

275
300325350
Annealing temperature (oC)375

Single MgOAs-depo.

Ta = 500 oC

EELS element map

B

OFe

Amo.-Ta(5)Amo.-Ta(B)Amo.-CoFeB(4)MgO(2.1)
Amo.-CoFeB(6)bcc-CoFe(B)
MgO
bcc-CoFe(B)
Amo.-TaB

Cry.-Ta(5)Cry.-TaTMR ratio (%)

700
600
500
400
300
2001000

S. Ikeda et al., Appl. Phys. Lett. 93(2008) 082508.
S. V. Karthik et al., J. Appl. Phys. 106 (2009) 023920.

250

300

350

400450500Annealing temperature (oC)550

11 nmφ MTJ (smallest MTJ to date)

H. Sato et al. Appl. Phys. Lett. 105, 062403 (2014)

Device size dependence of ∆10080

∆

60
40
20APL 2012
series1
series2

00 10 20 30 40 50 60 70 80 90
Junction diameter (nm)Dotted line reproduces the trend wellInterface engineering to further enhance ∆H. Sato et al., Appl. Phys. Lett. 101, 022414 (2012).
H. Sato et al., IEDM 2013, p. 3.2.1.
H. Sato et al. Appl. Phys. Lett. 105, 062403 (2014)

Demagnetization coefficient N2DE = K eff t   π
2Ki
M S2K eff =+ Kb −( Nz − Nx )t2 µ0

Reported properties of nano p-MTJs[1] S. Ikeda et al., Nature Mater. 9, 721 (2010).
[2] W. Kim et al., 2011 IEDM, p24.1.1[3] M. Gajek et al, Appl. Phys. Lett. 100, 132408 (2012).
[4] E. Kitagawa et al., 2012 IEDM, p. 29.4.2.
[5] L. Thomas et al., J. Appl. Phys. 115, 172615 (2014).
[6] J. H. Kim et al., 2014 VLSI Tech., P.76.
[7] H. Sato et al., 2013 IEDM, p. 61., Appl. Phys. Lett. 2014

Interface anisotropy – junction size, Ki and ∆Size dependence of ∆/IC0H. Sato et al., Appl. Phys. Lett. 101, 022414 (2012).
H. Sato et al., IEDM 2013, p. 3.2.1.
H. Sato et al. Appl. Phys. Lett. 105, 062403 (2014)

Magnetization manipulation by

Magnetic field
write/read heads for HDD
1st generation MRAM

Spin current

http://www.hitachigst.com/

http://www.everspin.com/

L. Berger, J. Appl. Phys. 55, 1954 (1984).
J. Slonczewski, J. Magn. Magn. Mat. 159, L1 (1996).
L. Berger, Phys. Rev. B 54, 9353 (1996).

Spin torque MRAM
Spin torque oscillator
Race-track memory

Electric field

R. Takemura et al., VLSI Circ. Dig. p.84 (2009)

Switching Energy

Spin-transfer switching
VIt = 0.25 (V) × 30 (µ A) × 1 (ns)= 8 (fJ)

Electric field switching
CV 2 =S × d × ε × E 230 (nm) 2) × 5 (nm) × 9.8 ε 0 × (5 (MV/cm)) 2= π(2= 0.08 (fJ)28

Electric-field control of magnets
Ferromagnetic transition

Ferromagnetic semiconductor (In,Mn)As50

22.5 K

Magnetization direction

Ferromagnetic Semiconductor (Ga,Mn)As2KR Hall (Ω)

2500V+1.5 MV/cm-1.5 MV/cm0V-25-50-1.0-0.500.5

1.0

B (mT)
H. Ohno et al., Nature 408, 944 (2000)

D. Chiba et al., Nature 455, 515 (2008)

Magnetization switching by anisotropy(1) perpendicular to in-plane and back(2) controlling in-plane anisotropies

Electric-field effects on metals
Room temperature

30 µeV/m2 per V/nm
Electric-field modulation of anisotropy in CoFeB
M. Endo, S. Kanai, S. Ikeda, F. Matsukura, and H, Ohno, Appl. Phys. Lett. 96, 212503 (2010).
See also; FePt, FePd: M. Weisheit et al., Science (2007). Fe/Au: T. Maruyama et al., Nature Nanotechnology (2009).

Electrical switching of perpendicular CoFeB

70 nmφS. Kanai et al., Appl. Phys. Lett. 101, 122403 (2012)Electrical switching of perpendicular CoFeB

under constant magnetic field
S. Kanai, et al., Appl. Phys. Lett. 101, 122403 (2012)
S. Kanai, et al., Appl. Phys. Lett. 103, 072408 (2013)
See also Y. Shiota et al. Nature Materials, 2011 for ultrathin FeCo
W. G. Wang et al. Nature Materials 2012 for electric-field assisted switching1.0tE = 1.3 ns 0.7 V⇒0.5 V

0.8
0.6
0.4

Vpulse = 0.5 V

0.2tE = 0 ns (only STT)

0.0024681012tE + tSTT (ns)1.0

Vpulse (V)Switching probability

Electrical switching plus STT

0.7 V

0.5 V

0.5tE + tSTT

0.0-0.5 tE=0.8 ns0Time

S. Kanai, et al., Appl. Phys. Lett. 104, 212406 (2014)

Remaining challenges
 Toggle: read before write Scaling: E=KV, ∆Ki=E/S
 Configuration: two terminal vs. three Switching probability
 Pulse: shape and timing control

Two and three terminal devices

Domain Wall

two terminal

three terminal

Nonvolatile, fast, low voltage and high enduranceDepinning probability of DW by ns pulses
0.5

0.0

1.00

N = 100

DW

1020

30

40

50

100

1.0

Exp.

10-2
10-4

Error rate

Current density (×1012 A/m2)

Current density, u (m/s)

10-6

0.5
DW-10

100.0

02

4

Calc.

10-8

68Pulse duration (ns)10tp = 2 ns
RT

10-12
0.0 0.2 0.4 0.6 0.8 1.0

Current density, j (1012 A/m2)

 Critical current density shows constant down to ~2 ns.
 Error rate decreases above a threshold more steeply than MTJs.
S. Fukami, H.O. et al., Nat. Commun. 4, 2293 (2013).

A New Paradigm in VLSIWhenever power consumption of LSI increased to hit a limit of heat dissipation,a paradigm shift in LSI technology has taken place by bringing in new technology.
Use of electron
charge only

Use of electron chargeand spin(magnetization)

Power Consumption

Power limitof a LSI198019902005

2015

YearSummarySpintronics devices are an indispensable ingredient indeveloping CMOS VLSI with low power and high performance.
Two terminal device
Size dependence of energy barrier of perpendicular
CoFeB-MgO MTJ between 30 and 11 nm; size
dependence of demagnetization.
Size dependence of ∆/IC0 suggests additional reduction ofdissipative path as size reduces.
Electric-field manipulation of magnetization
Three terminal device
Depinning probability that determines error rate wasexplored and shown to follow a function steeper than thatknown for MTJs.