magnetic tunnel junctions for spintronics applications

Department of Electronics, AGH University of Science and Technology

Amorphous and Nanostructered Magnetic Materials – ANMM’2015, Iasi, 21 – 24 September 2015

T. Stobiecki

Department of Electronics AGH, Poland

Magnetic Tunnel Junctions for

spintronics applications

1



Spintronics devices road map

Technology of magnetic tunnel junctions (MTJs)• sputtering

• nanofabrication (electron-litography)

Magnetization dynamics Spin Transfer Torque (STT)

• Current-Induced Magnetization Switching (CIMS) in MTJs with

in-plane and out-of-plane anisotropy STT-RAM

• New underlayer materials for MTJs with out-of-plane anisotropy

Conclusions

Motivation Green I(nformation) T(echnology)

2

Outline

Spin Diode Effect

Spin Hall Effect (SHE) in Ta,W/CoFeB



Magnetoresistance

MR ratio (RT & low H)

AMR effect

MR = 1~2%

Year

1857

1990

1995

2000

2005

2015

Lord Kelvin

TMR effect

MR = 20~70%

1985GMR effect

MR = 5~15%

T. Miyazaki, J. Moodera STT J. Slonczewski, L. Berger 19661996

Device applications

HDD head

Inductive

head

MR head

GMR head

TMR head MRAM

Memory

Giant TMR effect

MR = 200~1000%

MgO -TMR headSpin Torque

MRAM Microwave, E-control,

Spin Orbit Torque

Novel

devices

1967

A. Fert, P. Grünberg, 2007 – Nobel Prize

3


Amorphous and Nanostructered Magnetic Materials – ANMM’2015, Iasi, 21 – 24 September 2015 4

10-5

10-4

10-3

10-2

10-1

100

101

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

MTJ size (m2)

Samsung 2011

Avalanche 2010

MagIC-IBM 2010

TSMC&Qualcomm 2009

Toshiba2008 MagIC-IBM 2008

IBM2003

Everspin2010

Everspin2010Hitachi&Tohoku 2010

SONY 2005

Grandis 2010

Everspin 2010

　　　　　　　　　　　　　　　

Toshiba 2012

Wri

tin

g e

ne

rgy (

pJ/b

it)

MRAM

(Øersted field)

Spin-transfer torque (STT) - RAM

Voltage effect

STT+voltage effect

MRAM

STT-RAM

GREEN IT, Present status of writing energy for MRAM

Energy requiredfor data retention

(60 kBT)

Φ30nm Φ100nm

Target < 1 fJ/bitΦ10nm

Electric-currentbased control

after T. Nozaki AIST



Green IT

after S. Yuasa (2012)

5



Green IT

after S. Yuasa (2012)

6



Tunneling – Julliere’s model

Ferromagnetic-electrode 1 Ferromagnetic-electrode 2Insulator

7



Magnetic field switching

TMR = 100%

AP

P

8

Resistance switching by external magnetic field



TMR = 100%

Curent Induced Magnetization Switching - CIMS

Resistance switching ? → by spin polarized current from SpinTransfer Torque (STT)

„1”

„0”

AP

P

9



(001)MgO

FFT

Transmission electron Microscopy (TEM) of TMR multilayers

TEM EDX

L. Yiao, S. van Dijken Aalto Univ.

0.9nm

2.3

0.6 – 1.1

2.3

3

50

3

50

3

16

2

0.9

7

30

10

+ AF

10

details in poster P-5-39



Courtesy of

Singulus TIMARISMulti Target Module

Top: Target Drum with 10

rectangular cathodes; Drum

design ensures easy

maintenance;

Bottom: Main part of the

chamber containing LDD

equipment

Oxidation ModuleLow Energy Remote

Atomic Plasma Oxidation;

Natural Oxidation;

Soft Energy Surface

Treatment

Transport Module

(UHV wafer handler)

Soft-Etch Module

(PreClean, Surface

Treatment)

Cassette Module

(according to

Customer request)

Ultra – High – Vacuum Design: Base Pressure 5*10-9 Torr (Deposition Chamber)

High Throughput (e.g. MRAM): 9 Wafer/Hour (1 Depo-Module)

High Effective Up-time: 18 Wafer/Hour (2 Depo-Module)

Sputtering deposition (industrial process)

11



TMR & RA vs. MgO barrier thickness

W. Skowronski , T. Stobiecki, et al. J. Appl. Phys. (2010), 093917A. Zaleski, W. Skowroński , et al. Appl. Phys. (2012), 033903

12



Nanofabrication by electron-beam lithography

-1.0 -0.5 0.0 0.5 1.0

100

150

200

250

300

Resis

tance [O

hm

]

Voltage [V]

Nanopillar 3 step: e-beam litography, ion etching, lift-off

e-litography by RAITH system

13



Microsystem Ion sys 500 – Ar+ etching

Ta

RuCoFeB

MgO

Mass spectrometer

Nanofabrication by electron-beam lithography



dt

dmmHm

dt

dmeff

Magnetization dynamics LLG

precession damping

L(andau) L(ifszic) G(ilbert) dynamics

15



Spin Transfer Torque (STT)

Unpolarized

electrons

Polarized

electrons

Transmitted

electrons

Polarizer P Free layer M

Local magnetizationConduction Electrons Transfer of transverse

moment m

=

Torque

(Spin Torque ST)

ST tends to align M (anti-)parallel to P

Electron

flow

16



dt

dmmHm

dt

dmeff Mm

VolMMmm

VolM SS

)(||

precession dampingSTT

Spin Transfer Torque (STT)

17

Z

X=X’

Y

ZZ’ Y

Y’

Tunnel barrier

Free layer

Reference layer

θθ

𝝉⊥

𝝉∥

𝒎

𝑴

V >

0

𝐞−



STT – CIMSSpin Transfer Torque Curent Induced Magnetization Switching

I = ICritical

1,0 1,5 2,0 2,5

2

4

6

8

10

Pow

er

(nV

/Hz

0.5)

Frequency (GHz)

DC current

-0.1 mA

-0.5 mA

-1 mA

-1.5 mA

-1.7 mA

-1.8 mA

W.Skowroński, T.Stobiecki et al. APEX 5, 063005 (2012)

18



Zero-magnetic field STO

• Use of:– Perpendicular anisotropy of thin CoFeB on MgO

– Needed Ferromagnetic coupling between FL and RL (0.9 nm

MgO)

• In-plane STT-induced oscillations

W.Skowroński, T.Stobiecki et al. APEX 5, 063005 (2012)

19



out-of-plane component

-1.0 -0.5 0.0 0.5 1.0

-2

-1

0

1

2 1 nm MgO

0.9 nm MgO

(1

0-19 N

m)

I (mA)

W.Skowroński, T.Stobiecki et al. PRB 87, 094419 (2013) Heiliger, Stiles PRL 100, 186805, (2008)

-1.0 -0.5 0.0 0.5 1.0

-2

-1

0

1

2

(

10-1

9 Nm

)

I (mA)

||

||

ab initio calculations

Perpendicular torque is about 10 times smaller than torque in plane ||

in-plane component



CIMS – critical current Jc0 in MTJ with in-plane

anisotropy• MTJ with 0.96 nm MgO

barrier and CoFeB free layer2.3 nm

0

0 ln2

1τ

τ

VMH

TkJJ P

SC

Bcc

3536

P APAP PStability factor

exp2

Tk

VMH

B

SC

W.Skowroński, T.Stobiecki et al. JAP 107, 093917 (2010)

-1.0 -0.5 0.0 0.5 1.0

400

600

800

1000

P P

AP 1 ms

2.7 ms

7.3 ms

19.8 ms

53.7 ms

b)

R

esis

tan

ce (

Oh

m)

Voltage (V)

AP



MTJ with perpendicular anisotropy

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0 5Ta/10Ru/3Ta/0.75-1.25 FeCoB/1.28 MgO/5Ta/5Ru

5Ta/10Ru/3Ta/1.28 MgO/1.00-1.70 FeCoB/5Ta/5Ru

td = 0.75 nm

td = 1.07 nm

M/A

[em

u/c

m2]*

10

-5

FeCoB nominal thickness [nm]

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6 5Ta/10Ru/3Ta/0.75-1.25 FeCoB/1.28 MgO/5Ta/5Ru

5Ta/10Ru/3Ta/1.28 MgO/1.00-1.70 FeCoB/5Ta/5Ru

K*t

eff

ective [

mJ/m

2]

CoFeB effective thickness [nm]

KV = -5.33*10

5 [J/m

3]

KS = 3.40*10

-4 [J/m

2]

tt = 0.64 nm

KV = -5.30*10

5 [J/m

3]

KS = 0.78*10

-4 [J/m

2]

tt = 0.15 nm

Kv

Ks

Kefft = KVt + KS

details in oral presentation O-4-02



0 2 4 6 8 10 12 14 16 18 20-2,0

-1,6

-1,2

-0,8

-0,4

0,0

0,4

0,8

1,2

1,6

2,0

Jc [M

A/c

m2

]

ln (tp/to)

effS

B

C VHMe

I

0

Critical current

2eff a SH H M M in plane

4eff a SH H M

M out of plane

Perpendicular magnetization reduces the critical switching current several times!

CIMS critical current in MTJs with

perpendicular anisotropy

Jc0 = 7MA/cm2

Jc0 = -15MA/cm2

Jc0 = 1.3MA/cm2

Jc0 = -1.2MA/cm2

Stability factor= 63

M. Frankowski, T.Stobiecki et.al JAP, 117,223908 (2015)



Influence of under layer materials on perpendicular magnetic anisotropy and VCMA effect

W. Skowroński, T. Nozaki et al. Phys. Rev. B 91, 184410 (2015)

Under layer: X (5 nm)

(CoFe)80B20 (0.88 nm)

MgO (2.5 nm)

Ta (5 nm)

(CoFe)80B20 Ref.

Ta (5 nm)

Ru (5 nm)

X: Ag, Ir, CuN, Zr, Nb, W 100 150 200 250 300 350 400 450 5000

20

40

60

80

Ag

Ir

CuN

Zr

Nb

W

Slo

pe

of

vo

lta

ge

eff

ec

t (f

J/V

m)

Annealing temperature (oC)

100 200 300 400 500

-5

0

5

10 Ag

Ir

CuN

Zr

Nb

W

Hp

erp

,eff (

kO

e)

Annealing temperature (C)

• Ir buffer shows the largest anisotropy change with the high PMA of Ki,0=1.9 mJ/m2, but low annealing stability

• W buffer exhibits high annealing stability up to 450 oC with keeping high PMA and VCMA effect of about 50 fJ/Vm

200 250 300 350 400 450

0

10

20

30

40

50

60

Annealing Temperature (oC)

TM

R (

%)

Ag

Ir

CuN

Zr

Nb

W



Mixing RF current with oscillatingresistancegive DC component

Spin Diode Effect induced by Magnetic Field or STT

𝛿𝜃

0

10

5

10

-1

0

1

0 200 400 600

Vdc

Time

RF current

Oscillatingresistance

Spin diode DC voltage

𝛿𝑅

𝑅(𝜃0)

2 m

Bottom Top

BiasT

V

280 nm

520 nm

STT

A. Tulapurkar et al. Nature 438 , 339–342 (2005).



107

108

109

-6

-4

-2

0

2

4

VD

C[m

V]

Frequency [Hz]

Microwave losses sources and callibration



1. VNA losses analysis in microwave circuit elements

107

108

109

-6

-4

-2

0

2

4

VD

C[m

V]

Frequency [Hz]10

710

810

9

-6

-4

-2

0

2

4

VD

C (

mV

)

Frequency (Hz)

Before callibration After callibration

2. Impedance mismatch

Microwave losses sources and callibration

VNA callibration

10M 100M 1G0

50

100

Tra

nsfe

red

pow

er

(%)

Frequency (Hz)

Reflection coefficient

Delivered power to sample



𝑉𝑜𝑢𝑡 = 𝑉𝑑𝑐+ 𝑉𝑎𝑐= 𝛿𝑅𝑐𝑜𝑠 𝜔𝑡 + 𝛽 ×𝑉

𝑅 𝜃0cos 𝜔𝑡

=𝑉𝛿𝑅

2𝑅(𝜃0)𝑐𝑜𝑠𝛽 + cos(2𝜔𝑡 + 𝛽)

M. Harder, et al., Phys. Rev. B 84, 054423 (2011)T. Nozaki, et al., Nat. Phys. 8, 491 (2012),S. Ziętek, P. Ogrodnik, T. Stobiecki, J. Barnaś et al., Phys. Rev. B 91, 014430 (2015)

timeindependent

timedependent

Spin diode effect theory



𝑉𝑑𝑐=𝑉𝛿𝑅

2𝑅(𝜃0)𝑐𝑜𝑠𝛽



=𝑉𝛿𝑅


timeindependent

timedependent

M. Harder, et al., Phys. Rev. B 84, 054423 (2011)T. Nozaki, et al., Nat. Phys. 8, 491 (2012),S. Ziętek, P. Ogrodnik, T. Stobiecki, J. Barnaś et al., Phys. Rev. B 91, 014430 (2015)




𝑅 𝜃 = 𝑅𝑃+𝑅𝐴𝑃− 𝑅𝑃

21 − 𝑐𝑜𝑠 𝜃

GMR/TMR angular dependence

𝑈 = 𝐾||𝑠𝑖𝑛2 𝜃 − 𝑀𝑠 𝐻𝑒𝑥𝑡 ∙ 𝑒𝑀 −

𝑀𝑠

2𝜇0 𝑒𝑀𝑇 𝑁 𝑒𝑀 + 𝐻𝑐𝑜𝑢𝑝 𝑒𝑧

Stationary point specified by total magnetic energy

Uniaxialanisotropy

Zeemanenergy

Shapeanisotropy



=𝑉𝛿𝑅


Exchange coupling

anisotropy








GMR angular dependence


𝑀𝑠

2𝜇0 𝑒𝑀𝑇 𝑁 𝑒𝑀 + 𝐻𝑐𝑜𝑢𝑝 𝑒𝑧 + 𝐻𝑂𝑒 𝑒𝑧 ∙ 𝑒𝑀


Uniaxialanisotropy

Zeemanenergy

Shapeanisotropy



=𝑉𝛿𝑅


Exchange coupling

anisotropy

To calculate 𝛿𝜃 we use the LLG equation

𝑑𝑀

𝑑𝑡= −𝛾𝑒𝑀 ×𝐻𝑒𝑓𝑓 +

𝛼

𝑀𝑠𝑀 ×

𝑑𝑀

𝑑𝑡

Resistance changes in around the stationary point

𝛿𝑅 =Δ𝑅

2sin(𝜃0)𝛿𝜃

Oersted Field

component








GMR angular dependence


𝑀𝑠

2𝜇0 𝑒𝑀𝑇 𝑁 𝑒𝑀 + 𝐻𝑐𝑜𝑢𝑝 𝑒𝑧 + 𝐻𝑂𝑒 𝑒𝑧 ∙ 𝑒𝑀


Uniaxialanisotropy

Zeemanenergy

Shapeanisotropy



=𝑉𝛿𝑅


Exchange coupling

anisotropy

Resistance changes in around the stationary point

𝛿𝑅 =Δ𝑅

2sin(𝜃0)𝛿𝜃

Oersted Field

component

𝐴 = 𝜂

4𝑀𝑠

2Γ− 1 2𝛾𝑒2𝐼𝐻𝑂𝑒Δ𝑅 𝐻𝑒𝑥𝑡 +

𝑀𝑠

𝜇0𝑁𝑥 − 𝑁𝑦

Γ = 1 + 𝛼 2 2

Final expression for spin diode voltage

𝑽𝑫𝑪 = 𝑨 𝒔𝒊𝒏𝟐 𝜽𝝎𝟐−𝝎𝟎

𝟐 ∙𝒄𝒐𝒔 𝝍 − 𝝈𝝎∙𝒔𝒊𝒏 𝝍

𝝎𝟐−𝝎𝟎𝟐 𝟐

+𝝈𝟐𝝎𝟐

To calculate 𝛿𝜃 we use the LLG equation

𝑑𝑀

𝑑𝑡= −𝛾𝑒𝑀 ×𝐻𝑒𝑓𝑓 +

𝛼

𝑀𝑠𝑀 ×

𝑑𝑀

𝑑𝑡






1.8 2.0 2.2 2.4 2.6-50

0

50

Hco

up (

Oe)

Cu layer thickness (nm)

107

108

109

1010

-10

-5

0

5

107

108

109

1010

-10

-5

0

5

107

108

109

1010

-10

-5

0

5

196 Oe

61 Oe

32 Oe

Vd

c (

mV

)

Frequency (Hz)

AF „0” F

Vdc vs. Frequency at H = const

S. Zietek, T.Stobiecki, Appl.Phys.Lett. 107 (2015)



Optimization efficiency of spin diode effectSD efficiency for different Cu layer thickness

AMR [1] GMR [2] TMR [3]

Magnetoresistance [%] ~3% ~10% ~100%

Efficiency [V/W] 0.15 V/W ~0.3 - 2 V/W 11-1000V/W

Advantages / disadvantages

• Low efficiency• Cheap

fabrication

• Cheap fabrication• Relatively good

efficiency• Current in plain

• High efficiency• Complex fabrication

process• Easy to breakdown

[3] W. Skowroński, T. Stobiecki et al. Appl. Phys. Lett. 105, 072409 (2014)

[1] A. Yamaguchi, et al. Appl. Phys. Lett. 90, 182507 (2007)

[2] J. Kleinlein, et al., Appl. Phys. Lett. 104, 153507 (2014)



Spin-Orbit/Spin Hall Effect of Tungsten and Tantalum

Ta 5 nm

MgO 5 nmCoFeB 1.4 nm

SiO2

W 4 nm

MgO 5 nmCoFeB 1.3 nm

SiO2

𝐴𝑀𝑅 =𝑅 θ − 𝑅⊥𝑅∥ − 𝑅⊥

𝑐𝑜𝑠2θ

L. Liu et al. Science 336, 555 (2012)

0 50 100 150 200 250 300 350-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9 W 4 nm

Ta 5 nm

AM

R (

%)

Field angle (deg)

0.06%

0.8%

spin currents induced STT

I𝑅𝐹

H Mθ



Cooperation and financial support

AGH Department of Electronics:

M. Czapkiewicz (micromagnetic simulations, magnetoptics)

J. Kanak (structure: XRD, AFM/MFM)

W. Skowronski (e-lithography ACMiN AGH, TMR, CIMS,Spin-diode, ST-FMR)

P. Wisniowski (MR-sensors, noise measurements and analysis)

W. Powroźnik (technical service)

M.Frankowski, PhD student (micromagnetic simulations)

M. Dąbek, PhD student (noise in sensors)

S. Ziętek PhD student (e-lithography, multiferroics)

M. Cecot, PhD student (SHE/SOT, AFM/MFM, e-lithography)

J. Chęciński, PhD student (micromagnetic simulations)

P. Rzeszut, student (LabView programming, electronic service, measurements)

ACMiN AGH: A. Żywczak (e-litography, PLD deposition, magnetic measurements)

Singulus AG: J. Wrona (sputtering deposition at Singulus AG, CIPT-capres measurements)

IFM PAN: J. Barnaś (UAM), P. Balaz (UAM, ChU Prag), J.Dubowik, H.Głowiński, P.Ogrodnik (PW), F.Stobiecki

AIST, Japan: T. Nozaki, S. Yuasa, Y.Suzuzki

EPFL, Switzerland: J-Ph. Ansermet, A.Vetro

University of Bielefeld, Germany : G. Reiss

Aalto University, Espoo, Finland: S. van Dijken

36



We acknowledge Polish National Science Center GrantNo. Harmonia-DEC-2012/04/M/ST7/00799

We acknowledge the NANOSPIN Grant no. PSPB- 045/2010 from Switzerland through the Swiss Contribution

Acknowledgments

Nanoscale spin torque devices for spin electronics



Conclusions

• Successful fabrication of MTJ nanopillars with an

ultrathin MgO barrier.

• Spin Transfer Torque (STT) effect in MTJs has been

quantitatively analysed.

• Current Induced Magnetization Switching (CIMS) and ST-

oscillations in MTJs with in-plane and out-of-plane

anisotropy have been demonstrated.

• New highly thermally stable underlayers, W and Ir with

high out of plane anisotropy and Voltage-Controled

Magnetic Anisotropy (VCMA) has been analyzed.

• The Spin Diode Effect has been demonstrated as a very

useful tool for magnetization dynamics investigations of

different spintronics devices: AMR, GMR,TMR and SHE.

38



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39

magnetic tunnel junctions for spintronics applications

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