S. Yuasa, R. Matsumoto, A. Fukushima, H. Kubota, K. Yakushiji, T. Nakamura,

Y. Suzuki and K. Ando

Tunnel Magnetoresistance Effect and Its Applications

Collaborators

Canon Anelva Corp. (R & D of manufacturing technology)

Toshiba Corp.(R & D of Spin-MRAM)

Funding agencies

Osaka University (High-frequency experiment)

(1) Introduction

(2) Epitaxial MTJs with a crystalline MgO(001) barrier

(3) CoFeB / MgO / CoFeB MTJs for device applications

Outline

Electronics・diode ・transistor

LSI

Magnetics・magnetic recording ・permanent magnet

Hard Disk Drive(HDD)

SpintronicsBoth charge and spin of the electron is utilized for

novel functionalities.

Since 1988

Electron

Charge -e Spin

N

S

Spintronics

Magneto-resistance

What is “magnetoresistance” ?

A change in resistance by an application of H.

Magneto-Resistance ; MR

Resistance (R)

Magnetic field (H) 0

Magnetic field H required to induce MR change

Magnetoresistance ratio(MR ratio)

MR ratio at RT & a low H (~1 mT) is important for practical applications.

Year

1995

2000

2005

2010

MagnetoresistanceMR ratio (RT & low H)

1857

1985

1990

AMR effect MR = 1 ~ 2 % Lord Kelvin

GMR effectMR = 5 ~ 15 %

A. Fert, P. Grünberg(Nobel Prize 2007)

T. Miyazaki, J. Moodera TMR effectMR = 20 ~ 70 %

Tunnel magnetoresistance (TMR) effect

Tunnel barrier

FM electrode

FM electrode

Tunnel Resistance RP : low

Parallel (P) state

Tunnel Resistance RAP : high

Antiparallel (AP) state

Magnetic tunnel junction (MTJ)

MR ratio ≡ (RAP – RP) / RP (performance index)

Room-temperature TMR in 1995

MR ratios of 20 – 70% at RT

T. Miyazaki (Tohoku Univ.) J. S. Moodera

(MIT) Ferromag. electrode

Ferromag. electrode

Amorphous Al-O

Al-O – based MTJ

GMRヘッドの出現

0.01

0.1

1

10

100

1000

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AMR GMR TMR

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1990 1992 1994 1996 1998 2000 2002 2004 2006 20081990 1992 1994 1996 1998 2000 2002 2004 2006 2008Year

GMR head

■

TMR head

■■■

Rec

ordi

ng d

ensi

ty （

Gbi

t/in

ch2 ）

Recording medium

N SS N

N SS N

N SS N

Rotation

N SS N

N SS N

N SS N Read head

Write head

Next-generation read head is indespensablefor > 200 Gbit / inch2.

Head Medium

Technologies for HDD read head

Ward Line

Bit Line MTJ

“1”

“0”

Non-volatile memory

Magnetoresistive Random Access Memory (MRAM)

Freescale’s 4 Mbit-MRAM based on Al-O MTJs

Volume production since 2006.

Magnetoresistive Random Access Memory (MRAM)

CMOS

MTJBit Line

Write Line

n+ p n+

Word Line

Cross-section structure

<Advantages> Non-volatile, high speed, infinite write endurance, etc.

<Disadvantage>High-density MRAM is difficult to develop.

MR ratios > 150% at RT are required for developing Gbit-MRAM.

Year

1995

2000

2005

2010

1857

1985

1990

MR effects MR ratio (RT & low H)

Device applications

MR head

GMR head

TMR head

HDD head

Inductivehead

MRAM

Memory

Much higher MR ratios were required for next-generation devices.

AMR effect MR = 1 ~ 2 %

TMR effectMR = 20 ~ 70 %

GMR effectMR = 5 ~ 15 %

(1) Introduction

(2) Epitaxial MTJs with a crystalline MgO(001) barrier

(3) CoFeB / MgO / CoFeB MTJs for device applications

Outline

Theoretical prediction of giant TMR effect in Fe/MgO/Fe

・Butler et al., Phys. Rev. B 63, 056614 (2001).

・Mathon & Umerski, Phys. Rev. B 63, 220403 (2001).

< First-principle calculations >

MR ratio > 1000%

Fully epitaxial MTJ

Fe(001)

Fe(001)

MgO(001)

Tunnel barrier FM 1

e

FM 2

Parallel (P) stateTunnel resistnce: RP

D1↑ D1↓

Energy

D2↑ D2↓

EF EF

Spin polarization P

MR ≡ (RAP – RP) / RP = 2P1P2 / (1 – P1P2), ( )( ),

)()()()(

FF

FFEDEDEDED

P↓↑

↓↑+−

=αα

ααα α = 1, 2.

Spin polarization P

Tunnel barrier FM 1

e

FM 2

Energy

D1↑ D1↓

Energy

D2↑ D2↓

EF EF

Energy

Antiparallel (AP) stateTunnel resistnce: RAP

Tunneling process in MTJsAmorphous Al-O barrier

No symmetry

Various Bloch states tunnel incoherently.

Crystalline MgO(001) barrier

4-fold symmetry

MgO(001)

Fe(001)

Fe(001)

Δ2’ Δ5Δ1

Δ1

Δ1

Fe(001)

Al-O

Δ2’ Δ5Δ1

MR ratio < 100% at RT

Only the Bloch states with Δ1symmetry tunnel dominantly.

Fully spin-polarized Δ1 band in bcc Fe(001)

Fully spin-polarized Δ1 band⇒ Giant MR ratio is theoretically expected.

Not only bcc Fe but also many other bcc alloys based on Fe or Co have fully spin-polarized Δ1 band.

(e.g. bcc Fe1-xCox , Heusler alloys)

minority spin

majority spinΔ1↓

1.5

1.0

0.5

0.0

-0.5

E-E

F( e

V)

Γ H

Δ1↑

(001) direction

EF

Fully epitaxial Fe/MgO/Fe MTJ grown by MBE

Fe(001)(Pinned layer)

MgO(001)

Fe(001)(Free layer)

TEM image2 nm

S. Yuasa et al., Nature Materials 3, 868 (2004).

Magnetoresistance of epitaxial Fe/MgO/Fe MTJ

S. Yuasa et al., Nature Materials 3, 868 (2004).

MR = 247%

MR = 180%

-200 -100 0 100 2000

100

200

300

tMgO = 2.3 nm

T = 20 K

T = 293 K

MR

ratio

( %

)

H ( Oe )MTJs with a single-crystal MgO(001) barrier

Magnetoresistance of textured MgO-based MTJ

S. S. P. Parkin et al., Nature Materials 3, 862 (2004).

MTJs with a (001)-oriented poly-crystal (textured) MgO barrier

1995 20000

20406080

100120140160180200

MR

ratio

(%) a

t RT

Year

220

240

2005

260

Nancy

CNRS-CSIC

AIST [1]

AIST [2]

IBM [3]

Amorphous Al-O tunnel barrier

Crystal MgO(001) tunnel barrier

[1] Yuasa, Jpn. J. Appl. Phys. 43, L558 (2004). [2] Parkin, Nature Mater. 3, 862 (2004).[3] Yuasa, Nature Mater. 3, 868 (2004).

Up to 600% at RT

“Giant TMR effect”

(1) Introduction

(2) Epitaxial MTJs with a crystalline MgO(001) barrier

(3) CoFeB / MgO / CoFeB MTJs for device applications

Outline

1995 20000

20406080

100120140160180200

MR

ratio

(%) a

t RT

Year

220

240

2005

260

Nancy

CNRS-CSIC

AIST [1]

AIST [2]

IBM [3]Anelva - AIST [4]

Fe(001)MgO(001)

Fully epitaxialMTJ

Textured MTJFeCo(001)MgO(001)

[1] Yuasa, Jpn. J. Appl. Phys. 43, L558 (2004). [2] Parkin, Nature Mater. 3, 862 (2004).[3] Yuasa, Nature Mater. 3, 868 (2004). [4] Djayaprawira, SY, APL 86, 092502 (2005).

Amorphous Al-O tunnel barrier

Crystal MgO(001) tunnel barrier

AmorphousCoFeB

MgO(001)

MTJ structure for practical applications

Ru

Tunnel barrier

Free layer

Pinned layer

FM (Co-Fe)

AF layer (Pt-Mn or Ir-Mn)for exchange biasing

For MRAM & HDD read head

This structure is based on fcc (111).

MgO(001) cannot be grown on fcc (111).4-fold symmetry 3-fold symmetry

or

MTJ structure in as-grown state

◆Ideal for device applicationsThis structure can be grown on any kind of underlayers

by sputtering deposition at RT + post - annealing.

TexturedMgO(001)

AmorphousCoFeB

AmorphousCoFeB

Djayaprawira, SY, Appl. Phys. Lett. 86, 092502 (2005).

TEM image

Collaboration with Canon-Anelva

CoFeB / MgO / CoFeB - MTJ with practical structure

Standard bottom structure for MRAM and HDD head

3-fold

4-foldAmorphous

Free layerTunnel barrier

SyF structure

AF layer forexchange-

biasing

Pinned layer

Crystallinesymmetry

Amorphous CoFeB

Textured MgO(001)

Amorphous CoFeBCrystal-lization

Crystallization of CoFeB

Crystallization of CoFeB by post - annealing

Amorphous CoFeB

Textured MgO(001)

Amorphous CoFeB

As-grown MTJ

bcc CoFeB(001)

bcc CoFeB(001)Annealing

above 250 ºC

Because the Δ1 band in bcc CoFeB(001) is fully spin-polarized, CoFeB/MgO/CoFeB MTJs show the giant TMR effect.

S. Yuasa et al., Appl. Phys. Lett. 87, 242503 (2005).

MgO(001) layer acts as a template to crystallize amorphous CoFeB.

“Solid Phase Epitaxy”

Sputtering deposition

Standard sputtering machine in HDD industry

Canon-ANELVA C-7100 system

Thermally oxidized Si wafer (8 or 12 inch)

100 wafers a day !

φ 8 inch

Year

1990

1995

2000

2005

2010

MR head

GMR head

HDD head

MgO-TMR head

Inductivehead

Industrial applications

MRAM

Memory

Spin-torqueMRAM

Novel devices

Microwave, etc.

AMR effect MR = 1 ~ 2 %

TMR effectMR = 20 ~ 70 %

Giant TMR effectMR = 200 ~ 600 %

1857

GMR effectMR = 5 ~ 15 %

1985

TMR head

MR effects MR ratio (RT & low H)

GMRヘッドの出現

0.01

0.1

1

10

100

1000

■■

■

■

■ ■

■■

■

■■■

■■

■■

■

■

■

■ ■

■■

■

■■■

■■

AMR GMR TMR

■■

1990 1992 1994 1996 1998 2000 2002 2004 2006 20081990 1992 1994 1996 1998 2000 2002 2004 2006 2008Year

GMR head

■

TMR head

■■■

Rec

ordi

ng d

ensi

ty （

Gbi

t/in

ch2 ）

Recording medium

N SS N

N SS N

N SS N

Rotation

N SS N

N SS N

N SS N Read head

Write head

Next-generation read head is indespensablefor > 200 Gbit / inch2.

Head Medium

Technologies for HDD read head

MgO-TMR head for ultrahigh-density HDD

Wafer of MgO-TMR head

TEM image

MgO-TMR head

◆Commercialized in 2007.◆Density > 250 Gbit / inch2 achieved.◆Applicable up to 1 Tbit / inch2.

Cut

Inte-gration

20 nm

Magnetic shield (top lead)

MgO–MTJ

Permanent magnet

Magnetic shield (bottom lead)

Permanent magnet

Inte-gration

Year

1990

1995

2000

2005

2010

MR head

GMR head

HDD head

MgO-TMR head

Inductivehead

Industrial applications

MRAM

Memory

Spin-torqueMRAM

Novel devices

Microwave, etc.

AMR effect MR = 1 ~ 2 %

TMR effectMR = 20 ~ 70 %

Giant TMR effectMR = 200 ~ 600 %

1857

GMR effectMR = 5 ~ 15 %

1985

TMR head

MR effects MR ratio (RT & low H)

Spin-torque MRAM （SpinRAM）

MTJ

Ru

CoFe1 nm

CoFeB

MgO

CoFeB

CMOS

Write current density, JC0 ～ 2 x 106 A/cm2

M. Hosomi et al.(Sony), Technical Digest of IEDM 2005, 19.1.

JC0 of 5 x 105 A/cm2 is required for Gbit-scale SpinRAM.

SpinRAM having perpendicular magnetization

A CMOS integrated MTJ array

MTJ

Upper metal

Upper electrode

Bottom elctrodeReference layer

MgOStorage layer

50nm

A TEM image of 50 nm-sized MTJ

50 nm

Perpendicularly magnetized MTJ is a promising technology for

Gbit-scale Spin-RAM.

T. Kishi (Toshiba), SY et al., IEDM (2008) 12.6.

MgO(001)

or

JC0 < 106 A/cm2 achieved !

Perpendicularly-magnetized electrodes

Year

1990

1995

2000

2005

2010

MR head

GMR head

HDD head

MgO-TMR head

Inductivehead

Industrial applications

MRAM

Memory

Spin-RAM

Novel devices

Microwave, etc.

AMR effect MR = 1 ~ 2 %

TMR effectMR = 20 ~ 70 %

Giant TMR effectMR = 200 ~ 600 %

1857

GMR effectMR = 5 ~ 15 %

1985

TMR head

MR effects MR ratio (RT & low H)

: commercialized

: perspectives

: commercialized

: perspectives