Magnetic Tunnel Junctions for spintronics...

Department of Electronics, AGH University of Science and Technology

The European Conference Physics of Magnetism, June 23 – 27, 2014, Poznań

T. Stobiecki

Department of Electronics AGH, Poland

Magnetic Tunnel Junctions for spintronics

applications

1



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-litography, multiferroics)

M.Banasik, gradueted student

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), J.Dubowik, H.Głowiński, P.Ogrodnik (PW), F.Stobiecki

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

University of Bielefeld, Germany : G.Reiss

Aalto University, Espoo, Finland: S. van Dijken

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Spintronics devices road map

Commercial spintronics devices • head TMR/HDD

• M-RAM, STT-RAM

Technology of magnetic tunnel junctions (MTJs) • sputtering

• nanofabrication (electron-litography)

Magentizations dynamics Spin Transfer Torque • current Induced Magnetization Switching (CIMS) in MTJs with

in plane and out of plane anizotropy STT-RAM

• spin dynamics: ST-FMR ST- Oscillator

Voltage-induced magnetic anistropy

• Static anisotropy changes – tunable sensor

• voltage induced precession

•rectification of spin polarized rf current in multiferroics PMN-PT/NiFe

Conclusions

Motivation Green I(nformation) T(echnology)

3

Outline



Magnetoresistance

MR ratio (RT & low H)

AMR effect

MR = 1~2%

Year

1857

1990

1995

2000

2005

2013

Lord Kelvin

TMR effect

MR = 20~70%

1985 GMR effect

MR = 5~15%

T. Miyazaki, J. Moodera STT J. Slonczewski, L. Berger 1996

Device applications

HDD head

Inductive

head

MR head

GMR head

TMR head MRAM

Memory

Giant TMR effect

MR = 200~1000%

MgO -TMR head Spin Torque

MRAM Microwave, E-control.

Novel

devices

1967

A. Fert, P. Grünberg, J. Barnaś

4



Green IT

after S. Yuasa (2012)

5



Green IT

after S. Yuasa (2012)

6



Tunneling – Julliere’s model

Ferromagnetic-electrode 1 Ferromagnetic-electrode 2 Insulator

7



Magnetic field switching

TMR = 100% AP

P

8



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 TIMARIS Multi Target Module

Top: Target Drum with 10

rectangular cathodes; Drum

design ensures easy

maintenance;

Bottom: Main part of the

chamber containing LDD

equipment

Oxidation Module Low 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), 093917 A. 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


The European Conference Physics of Magnetism, June 23 – 27, 2014, Poznań 14

Microsystem Ion sys 500 – Ar+ etching

Ta

Ru CoFeB

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 magnetization Conduction 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 damping STT

Spin Transfer Torque (STT)

17



Zero-magnetic field STO

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

– 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)

18



Spin Torque vs. ST-FMR

19

•MTJ sample placed in the magnetic field

and tilted by a certain degree

•amplitude modulated RF current

supplied to the MTJ through a bias tee

•small DC voltage (Vmix) measured by

voltmeter or lock-in detection

0

2

4

6

8

10

12

0

10

20

30

40

50

3 4 5 6 70

5

10

15

20

600

550

500

450

400

350

300

250

200

150

a) 1.01 nm

b) 0.95 nm

450

400

350

300

250

Vm

ix (V

)

External magnetic field (Oe)

700

650

600

550

500

Frequecy (GHz)

c) 0.76 nm

300

250

200

150

100

550

500

450

400

350

0

5

10

15

20

-1,0 -0,5 0,0 0,5 1,0

0

5

10

15

20

HEXT

MREF

a) = 70° FL1 exp

FL2 exp

FL sim

RL sim

Fre

qu

en

cy (

GH

z)

b) = 30° FL exp

RL exp

FL sim

RL sim

Field (kOe)

HEXT

MREF

Frequency



ASI

VoleMI

VRF

S

||

22

4

sin

2

1

20

Torkances and torques

•Vmix is derived from the LLGS equation

2

2

2

4

1RFmix I

I

VV

•S and A are symmetric and asymmetric

lorentzians:

dV

dT

dI

dVe ||

|| sin2

dV

dT

dI

dVe sin

2

Wang et al. PRB 79, 224416, 2009

6 7 8 9

-10

0

10

0 .25 V

0.1 V

0 V

-0.1 V

-0.25 V

V m

ix (

uV

)

Frequency (GHz)

6 7 8 9-8

-4

0

4

8

12

0.1 V

S + A fit

S

A

V m

ix (

uV

)

Frequency (GHz)



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



STT – CIMS Spin 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)

22



CIMS – critical current Jc0 in MTJ with in plane

anisotropy • MTJ with 0.96 nm MgO

barrier and CoFeB free layer 2.3 nm

0

0 ln2

1τ

τ

VMH

TkJJ P

SC

Bcc

35 36

P AP AP P Stability 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 [m

J/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 magnetisation reduces the critical switching current

about 10 times!

CIMS critical current in MTJs with

perpendicular anisotropy

Jc0 = 7MA/cm2

Jc0 = -15MA/cm2

Jc0 = 1.3MA/cm2

Jc0 = -1.2MA/cm2



Voltage-tunable magnetic field sensor

• bias voltage changes the perpendicular

magnetic anisotropy +V increase out of plane

anisotropy

• thin CoFeB layer

• Thick MgO (1.35 nm) – no STT present

W.Skowroński, P.Wiśniowski et al. APL 101, 192401, 2012

26



Voltage-induced dynamics

• MTJ with thick MgO (2nm) – high resistance, low current

• voltage-induced FMR precession in MTJ

• the resonance frequency change of 97MHz/V which corresponds to the

change in the perpendicular magnetic anisotropy of 4 kJ/m3/V

W. Skowroński, T. Stobiecki et al. MMM2013

-300 -200 -100 0 100 200

0.0

0.2

0.4

0.6

0.8

1.0

No

rma

lize

d T

MR

Field (Oe)

Bias voltage (V)

0.01

0.6

-0.6

1.0 1.5 2.0 2.5

-0.2

-0.1

0.0

0.1

0.2 -1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Voltag

e (

mV

)

Frequency (GHz)

Bias voltage (V):

27


600 Oe



θ=30⁰

θ

H


+80 V

-80 V

27 Oe

AMR =0.75%

Rectification of spin polarized rf current in PMN-PT/NiFe

frequency shift 0.25GHz



Conclusions

• Successful fabrication of MTJ nanopillars with a ultrathin

MgO barrier.

• Spin Transfer Torque (STT) effect in MTJs was

quantitavely analysed.

• Current Induced Magnetization Switching (CIMS) and

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

plane anizotropy were demonstrated.

• Voltage-Induced magnetic anisotropy – tunable sensor

and RF-signal detection were demonstrated.

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