T.Stobiecki Katedra Elektroniki AGH

Magnetic Tunnel Junction (MTJ)or

Tunnel Magnetoresistance (TMR)or

Junction Magneto- Resistance (JMR)

11 wykład 13.12.2004

Spin Polarization, Density of States

Ferromagnetic metal (Fe)

nn

nnP

Spin Polarization Density of states 3d

Ni 33 %

Co 42 %

Fe 45 %

Ni80 Fe20 48 %

Co84 Fe16 55 %

CoFeB 60%

Material Polarizations

Normal metal (Cu)

E F

M a jor ity Sp in M ino rity Spin

E

DOS

nn

)()( FF EnEn )()( FF EnEn

N

E F

M a jo rity Sp in M ino rity Sp in

E

DOS

nn

Tunneling in FM/I/FM junction

II

III

nn

nnP

IIII

IIIIII

nn

nnP

III

III

M

MM

PP

PP

I

IITMR

1

2

R

RRTMR

IIIIIIM

nnnnI

IIIIIIM

nnnnI

II

I I

FM I (PI) FM II (PII)

Barrier

eV N

E F

M a jo rity Sp in M ino rity Sp in

E

DOS

nn

N

E F

M a jo rity Sp in M ino rity Sp in

E

DOS

nn

E F

M a jori ty Sp in M ino rity Spin

E

DOS

Nnn

Type of MTJs

Standard junction

FM

I

FM

FM

I

FM

I

FM

Spin valve junction(SV- MTJ)

Double barrier junction

B

AF

FM

I

FM

Application-Oriented Properties of S-V MTJ

• Tunnel Magnetoresistance -TMR

• Resistance area product -RxA

• Interlayer coupling field HS

• Exchange bias field HEXB

• Coercive field pinned HCP

and free HCF layer

• Switching field HSF

Magnetic

Materials

• I (Al-O,MgO..)

• FM (Co, CoFe, NiFe)

• AF (MnIr, PtMn, NiO)

• Buffer (Ta,Cu, NiFe)

Treatment

• Annealing

• Field cooling

Preparation

• Sputtering deposition

• Oxidation

SV-MTJ

Electric

Magnetic and Electric Parameters

B

AF

FM II (Pinned)

I

FM I (Free)Interlayer coupling

HSExchange coupling

HEXB

HSF switching fields

HS

HEXBHCP

HCF

HSF

R

RRTMR

Applications of SV-MTJ

M-RAM

SPIN-LOGIC READ HEADS

SENSORS

SV-MTJ

SV-MTJ Based MRAM

Bit lines

Word lines

IB

IW

Writing “0”

Writing “1”

IB

Memory Cell

Reading current IR

Memory Matrix

SV-MTJ

IW

Writing - rotation of the free layer

Reading - detection of a resistance of a junction

SV- MTJ as MRAM component must fulfill requirements - Thermal stability- Magnetic stability - Single domain like switching behaviour- Reproducibility of RxA, TMR and Asteroids

Hy/

H(0

)

1

-1

-1 10

0

Critical switching fields Hx , Hy (S-W) asteroid

Motorola: S.Tehrani et al. PROCEEDINGS OF THE IEEE, VOL. 91, NO. 5, MAY 2003

Features of M-RAM - Non-volatility of FLASH with fast programming, no program endurance limitation

- Density competitive with DRAM, with no refresh

- Speed competitive with SRAM

- Nondestructive read

- Resistance to ionization radiation

- Low power consumption (current pulses)

• Single 3.3 V power supply

• Commercial temperature range (0°C to 70°C)

• Symmetrical high-speed read and write with fast access time (15, 20 or 25 ns)

• Flexible data bus control — 8 bit or 16 bit access

• Equal address and chip-enable access times

• All inputs and outputs are transistor-transistor logic (TTL) compatible

• Full nonvolatile operation with 10 years minimum data retention

Motorola: S.Tehrani et al. PROCEEDINGS OF THE IEEE, VOL. 91, NO. 5, MAY 2003

SV-MTJ Based Spin Logic Gates

Siemens & Univ. Bielefeld: R. Richter et al. J. Magn.Magn. Mat. 240 (2002) 127–129

SV- MTJ as spin logic gates must fulfill requirements  - Thermal stability- Magnetic stability - Centered minor loop- Single domain like switching behaviour- Reproducibility of R, TMR

RMTJ2

Logic Inputs

Logic Output

Programing Inputs

SV-MTJs

RMTJ3

RMTJ1

RMTJ4

(+, ) IB

(+, ) IA

IS

ISVO UT

VOUT= IS(RMTJ3 + RMTJ3 – RMTJ1 – RMTJ2)

Logic Inputs MTJ 3, MTJ 4

0

2 VOUT

(0,0) (1,1)(1,0)(0,1) (0,0) (1,1)(1,0)(0,1)

MTJ 1 MTJ 2 MTJ 1 MTJ 2

NAND NOR

„1"

„0"

Lo

gic

Ou

tpu

t

-2 VOUT

Features of Spin Logic Gates

- Programmable logic functions (reconfigurable computing)

- Non-volatile logic inputs and outputs

- Fast operation (up to 5 GHz)

- Low power consumption

- Compatibility to M-RAM

SV-MTJ Based Read Heads

SV-MTJ as a read sensor for high density (> 100Gb/in2) must fulfill requirements  - Resistance area product (RxA) < 6 -m2 - High TMR at low RxA

Experiments on SV -MTJsA MTJs

3 6 10 30 50

Substrate Si (100)

Cu 25 nm

MnIr 12 nm

CoFe t nm

Al2O3 1.4 nm

NiFe 3 nm

Ta 5 nm

Cu 30 nm

Ta 3 nm

Au 25 nm

0 10 30 60 100

Substrate Si (100)

SiO2

Ta 5 nm

Cu 10 nm

Ta 5 nm

NiFe 2 nm

Cu 5 nm

MnIr 10 nm

CoFe 2.5 nm

Al2O3 1.4 nm

CoFe 2.5 nm

NiFe x nm

Ta 5 nm

B MTJs

A structure prof. G. Reiss laboratory University BielefeldB structure prof. T. Takahasi laboratory, Tohoku University

10 mm

Junction

Junction

Junctions size (180180) m2

Effect of Annealing on TMRAs deposited Annealed

-150 -100 -50 0 50 100 1500

2

4

6

8

10

12

14

TMR = 13.4 %

TM

R [%

]

H [kA/m]

100 150 200 250 300 3500

5

10

15

20

25

30

35

40

TM

R [%

]

Annealing temperature (oC)

100 nm (10 sec) 100 nm (13 sec) 100 nm (16 sec) 10 nm (10 sec) 10 nm (13 sec) 10 nm (16 sec)

-120 -80 -40 0 40 80 1200

10

20

30

40

50

TMR = 48 %

TM

R [%

]

H [kA/m]

10 mm

H=80 kA/m

annealing 1 hour in vacuum 10-6 hPa

Interlayer and Exchange Coupling Fields

A MTJs B MTJsExchange coupling fields Interlayer coupling fields

-100 -75 -50 -25 0 25 50-3

-2

-1

0

1

2

3

Ke

rr r

ota

tion

[min

]

H [kA/m]

3nm 6nm 10nm 30nm 50nm

-3000 -2500 -2000 -1500 -1000 -500 0 500 1000 1500-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Ke

rr r

ota

tion

[min

]

H [A/m]

10 nm 30 nm 60 nm 100 nm

-100 -75 -50 -25 0 25 500

10

20

30

40

50

3nm 6nm 10nm 30nm 50nm

TM

R [

%]

H [Oe]

-3000 -2000 -1000 0 1000 2000 3000

0

10

20

30

40

TM

R[%

]

H [Oe]

10 nm 100 nm

Interlayer and Exchange Coupling Fields

FFS tM

JsH

0

PP

EXBEXB tM

JH

0

Temperature Dependence of TMR

)()()( TGTGTdG APP

AP

APP

G

GGTMR

P. Wiśniowski, M.Rams,... Temperature dependence of tunnel magnetoresistance of IrMn based MTJ, phys. stat. sol (2004)

-40 -30 -20 -10 0 10 20

0

10

20

30

40

50

30K 50K 70K100K150K200K250K300K

TM

R [

%]

H [Oe]

t=10nm (3000 C)

-20 -15 -10 -5 0 5 10 15 200

10

20

30

40

50

60t=100nm (2700 C)

TM

R[%

]

H [Oe]

30k 50k 70k 100k 150k 200k 250k 300k

Total Conductance

)()]()(1)[()( 21 TGTPTPTGTG SITAP )()]()(1)[()( 21 TGTPTPTGTG SITP

)()()(2)()()( 21 TPTPTGTGTGTdG TAPP

)sin(/)( 0 CTCTGTGT )1()1()()( 2/3202

2/310121 TbPTbPTPTP

Varies slightly with T Varies with T as magnetization does Bloch law

Negligible

Dominant

)()]cos()()(1)[(),,( 212121 TGTPTPTGTG SIT

AP

APP

G

GGTMR

Polarization, Bloch Law )()()(2)( 21 TPTPTGTdG T

][102.9[%]45

][100.1[%]482/36

202

2/36101

KbP

KbP100 nm

AP

P

1. Set H= – 2000 Oe

2. Cooling H= 500 Oe

3. Measured M (T)1. Set H= – 2000 Oe

2. Cooling H= –500 Oe

3. Measured M (T)

)1()( 2/30 BTMTM

][1099.6

][1076.62/36

2/36

KB

KB

Spin Independent ConductanceTAPPSI GGGG 2/)(

NTGSI

66.1

][1021.3 6

SKN

33.1

][100.2 6

SKN

Hopping conductance, low level of defects

Hopping conductance, high level of defects

TIMARIS: Tool status

Tool #1 – process optimization on 200 mm wafers since mid of March 03

Tool #2 – The Worlds 1st 300 mm MRAM System is Ready for Process in August 03

Multi (10) Target Module

Oxidation / Pre-clean Module

Transport Module

Clean room

Sputtering System

Metal depo.

Plasma Oxidation

LL １ : wafer-in

LL ２ : Bridge Reactive

sputter : surface smooth

Measurements R-VSMMOKE

Sample

H coilsy

H coilsx

MOKE with Orthogonal Coils