Tunnel Magnetoresistance Effect and Its Applications S. Yuasa, R. - - PowerPoint PPT Presentation

• 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)

Spintronics

Both 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) 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

Magnetoresistance MR ratio (RT & low H)

1857 1985 1990

AMR effect MR = 1 ~ 2 %

Lord Kelvin

GMR effect MR = 5 ~ 15 %

• A. Fert, P. Grünberg

(Nobel Prize 2007)

• T. Miyazaki, J. Moodera

TMR effect MR = 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

■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■

AMR GMR TMR

■ ■

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

Year GMR head

■

TMR head

■ ■ ■

Recording density （Gbit / inch2）

Recording medium

N S S N N S S N N S S N

Rotation

N S S N N S S N N S S N

Read head

Write head

Next-generation read head is indespensable for > 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

MTJ

Bit 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

Inductive head MRAM

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

AMR effect MR = 1 ~ 2 % TMR effect MR = 20 ~ 70 % GMR effect MR = 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) state Tunnel resistnce: RP D1↑ D1↓

Energy

D2↑ D2↓

EF EF

Spin polarization P

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

( ) ( )

, ) ( ) ( ) ( ) (

F F F F

E D E D E D E D P

↓ ↑ ↓ ↑

+ − =

α α α α α α = 1, 2.

Spin polarization P

Tunnel barrier

FM 1

e

FM 2

Energy

D1↑ D1↓

Energy

D2↑ D2↓

EF EF

Energy

Antiparallel (AP) state Tunnel resistnce: RAP

Tunneling process in MTJs

Amorphous Al-O barrier No symmetry Various Bloch states tunnel incoherently. Crystalline MgO(001) barrier 4-fold symmetry MgO(001) Fe(001) Fe(001)

Δ2’ Δ5

Δ1 Δ1 Δ1

Fe(001) Al-O

Δ2’ Δ5 Δ1 MR ratio < 100% at RT

Only the Bloch states with Δ1 symmetry 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

• n Fe or Co have fully spin-polarized Δ1 band.

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

minority spin majority spin

Δ1↓

1.5 1.0 0.5 0.0

• 0.5

E - EF ( eV ) 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 image 2 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

100 200

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 2000 20 40 60 80 100 120 140 160 180 200

MR ratio (%) at 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 2000 20 40 60 80 100 120 140 160 180 200

MR ratio (%) at RT

Year

220 240 2005 260

Nancy CNRS-CSIC AIST [1] AIST [2] IBM [3] Anelva - AIST [4] Fe(001) MgO(001) Fully epitaxial MTJ Textured MTJ FeCo(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

Amorphous CoFeB 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

• r

MTJ structure in as-grown state ◆Ideal for device applications This structure can be grown on any kind of underlayers by sputtering deposition at RT + post - annealing.

Textured MgO(001) Amorphous CoFeB Amorphous CoFeB 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-fold

Amorphous Free layer Tunnel barrier SyF structure AF layer for exchange- biasing Pinned layer Crystalline symmetry

Amorphous CoFeB Textured MgO(001) Amorphous CoFeB

Crystal- 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 Inductive head

Industrial applications

MRAM

Memory

Spin-torque MRAM

Novel devices

Microwave, etc. AMR effect MR = 1 ~ 2 % TMR effect MR = 20 ~ 70 % Giant TMR effect MR = 200 ~ 600 %

1857

GMR effect MR = 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 2008 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

Year GMR head

■

TMR head

■ ■ ■

Recording density （Gbit / inch2）

Recording medium

N S S N N S S N N S S N

Rotation

N S S N N S S N N S S N

Read head

Write head

Next-generation read head is indespensable for > 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 Inductive head

Industrial applications

MRAM

Memory

Spin-torque MRAM

Novel devices

Microwave, etc. AMR effect MR = 1 ~ 2 % TMR effect MR = 20 ~ 70 % Giant TMR effect MR = 200 ~ 600 %

1857

GMR effect MR = 5 ~ 15 %

1985

TMR head

MR effects MR ratio (RT & low H)

Spin-torque MRAM （SpinRAM）

MTJ

Ru CoFe 1 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 elctrode Referenc e layer MgO Storage 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)

• r

JC0 < 106 A/cm2 achieved ! Perpendicularly-magnetized electrodes

Year

1990 1995 2000 2005 2010

MR head GMR head

HDD head

MgO-TMR head Inductive head

Industrial applications

MRAM

Memory

Spin-RAM

Novel devices

Microwave, etc. AMR effect MR = 1 ~ 2 % TMR effect MR = 20 ~ 70 % Giant TMR effect MR = 200 ~ 600 %

1857

GMR effect MR = 5 ~ 15 %

1985

TMR head

MR effects MR ratio (RT & low H) : commercialized : perspectives : commercialized : perspectives