Spin-transfer related phenomena in magnetic tunnel junctions - - - PowerPoint PPT Presentation

Spin-transfer related phenomena in magnetic tunnel junctions

• Interplay of the giant tunneling magneto-resistance and spin-torque effect -

JST-DFG workshop on Nanoelectronics, 21.23.01.2009 in Kyoto

Yoshishige Suzuki1,2

Acknowledgements

• H. Maehara3, A. Deac1, 2,*, T. Maruyama1, Y. Shiota1 , T. Nozaki1,
• H. Kubota2, A. Fukushima2, S. Yuasa2,
• K. Tsunekawa3, D. D. Djayaprawira1, 3, and N. Watanabe3

1Osaka University, Graduate School of Engineering Science, Osaka, Japan 2NanoElectronics Research Institute, National Institute of Advanced Industrial Science

and Technology, Tsukuba, Japan

3Electron Device Equipment Division, Canon ANELVA Corporation, Japan.

JST, NEDO, SCOPE of MIC and G-COE of MEXT for financial supports

S p i n a n d e l e c t r

• n

i c s

spin: electron is a small manget charge: electron brings electricity

（c h a r g e ） M a g n e t i s m （s p i n ） S e m i c

• n

d u c t

• r

e l e c t r

• n

i c s

• e

N-pole S-pole rotation (spin) charge

S p i n t r

• n

i c s

① GMR/TMR

(Giant magneto-resistance / Tunneling magneto-resistance)

Magetization→Conduction

GMR

Grünberg / Fert 1988 AlO-Mangetic tunnel junction Miyazaki / Moodera 1995 MgO-Mangetic tunnel junction

Yuasa / Parkin 2004

+

• +

Development of Magnetic Tunnel Junctions

‘95 ‘00 ‘05 ‘10

MPI AIST AIST[1] Anelva-AIST AIST[2]

MgO (001) barrier

Tohoku MIT IBM Fujitsu IBM Tohoku Sony NVE

CNRS Nancy IBM Tohoku Tohoku Tohoku

Al-O barrier

600 400 200 MR (%) at RT Year

[1] S. Yuasa, Y. S. et al, Nature Materials, 3(2004)868.

• A. C. C. Yu, et al., JJAP 40, 5058 (2001)

Al-O barrier MTJ MgO(001) barrier MTJ

Fe(001) Fe(001)

MgO(001)

Spintronics & Spin-transfer phenomena

① GMR/TMR

(Giant magneto-resistance / Tunneling magneto-resistance)

Magetization→Conduction

② Spin-injection magnetization switching

Conduction→Magetization

Spin-transfer theory

Slonczweski / Berger 1996 Spin-transfer switching (GMR) Myers 1999

Switching (MgO TMR)

Kubota / Huai / Hayakawa 2005

＋ － ＋ －

② Spin-injection magnetization switching

Conduction→Magetization

Current induced domain wall motion

Yamaguchi, Ono/Vernier Tatara and Kohno 2004

Spin Torque

d s s Conduction electrons (s) are scattered by Local moments (d) Spin conservation in the s-d interaction Reduction of Ss = Increase of Sd

S1

current

S1 S2

s d s

Spin polarizer

∑

> 0

s

s

∑

= 0

s

s

Exchange scattering Spin-transfer model FM1 FM2

G M R : C

• r

n e l l U n i v e r s i t y , N a t u r e ( 2 3 ) H i g h p

• w

e r

• u

t p u t u s i n g a n M g OM T J : O s a k a U n i v . / A I S T / C a n

• n

A N E L V A A . D e a c , Y . S . e t a l . , N a t u r e P h y s . ( 2 8 ) G M R : C

• r

n e l l U n i v e r s i t y , S c i e n c e ( 1 9 9 9 ) M g OM T J : A I S T , J J A P ( 2 5 ) P e r p . M T J : T

• s

h i b a , A P S m e e t i n g ( 2 8 ) H i g h s p e e d s w i t c h i n g ( 2 p s e c ) , A . T u l a p u r k a r , Y . S . , e t a l . , A P L ( 2 5 )

② Spin-injection magnetization switching

Conduction→Magetization

③ Spin-transfer oscillation

d.c. current→RF oscillation

Spintronics & Spin-transfer phenomena

④ Spin-torque diode RF current →d.c. voltage

• A. Tulapurkar, Y. S., et al.,(TMR)

Nature, 438(2005)339.

• J. C. Sankey et al.,(GMR)
• Phys. Rev. Lett., 96(2006)227601

① GMR/TMR

(Giant magneto-resistance / Tunneling magneto-resistance)

Magetization→Conduction

② Spin-injection magnetization switching

Conduction→Magetization

③ Spin-transfer oscillation

d.c. current→RF oscillation

(A) Up to down current makes magnetization parallel and resistance small. Thus it produces small negative voltage. (C) Down to up current makes magnetization anti-parallel and resistance large. Thus it produces large positive voltage. (B) No current : Shape anisotropy prefers vertical alignment

Spin-torque diode effect

Curernt

V

• +

+

• Current Source

Curernt

• +

V

• +

Current Source

V

• +
• A. Tulapurkar, Y. S., et al., Nature, 438(2005)339

Voltage dependece of the spin-toruqes

Spin-transfer torque

Vc: AP->P switching

• H. Kubota, Y. S., et al. Nature Phys. (2007)

θ θ sin / : Torquance cos / : e Conductanc T V Torque G G V I = ∆ + =

Charge current and Spin current

• J. C. Slonczewski, PRB (2005)

実験

Negative resistance and amplification in MgO-MTJs

• H. Maehara

Canon ANELVA

5th function of MTJs

Spin torque

Spontaneous oscillation∗ : D.C. ⇒ RF signal Spin torque diode effect∗∗ (detection) : RF ⇒ D.C. Signal

Characteristics are the same as “Esaki diode” !!

FM FM NM

MR devices Esaki diode

≈

Esaki diode has ability of amplifier. What about MR devices ?

Negative resistance gives the ability of amplification

“Esaki diode shows the Negative Resistance and it gives ability of amplification.”

I V

Negative resistance region

V ∆

I ∆

< ∆ ∆ = ∆ I V R

in

V

• V

RL RT < 0

T

V

V

L

V

( ) ( )

I I R I I V V V

L T in

∆ + ⋅ + ∆ + = +

( )

Gain R R R V V

L T L in L

= + =

Load resistance : RL

• V

1 >

Amplification!

We must realize the negative resistance in I-V characteristics.

<

AF

Small angle oscillation

I I

c

AP state P state

AF

Free

External field I Resistance = low state

AF

Large angle oscillation

C a s e

• f
• s

c i l l a t i

• n

C a s e

• f
• s

c i l l a t i

• n

V

Sample structure and deposition method

Equipment : “Canon ANELVA C-7100” Sputtering method : DC magnetron sputtering for metals RF magnetron sputtering for MgO with Ta paste process∗ Base pressure : ~ 10-9 Torr Anneal condition : 360 ℃/ 2h / 8 kOe Free layer : 2 nm Sample structure

CoFe (2.5 nm) AF layer Ru (0.85 nm) CoFeB (3 nm) Capping layer Bottom electrode CoFeB (2 nm) MgO sub. MgO (1.12 nm)

We obtained high MR ratio at low resistance

∗N. Nagamine, et al., APL

RF magnetron sputtering for MgO with Ta paste process∗

• 1000
• 500

500 1000 400 600 800 1000 1200 1400

Resistance (Ω) H (Oe)

RA = 4.9 Ωµm2 MR = 167 %

Micro fabrication

1) Patterning with EB lithography, Ion milling processes

100 nm

Resist

100 nm

Resist

Bottom lead pad Junction area Bottom electrode Sub Bottom lead pad Junction area Bottom electrode Sub

3) Electrode pad formation and measurement

Upper electrode Bottom electrode Upper electrode Bottom electrode

2) SiO2 deposition and lift off processes

Contact hole SiO2 Contact hole SiO2 SiO2 SiO2

100 nm

Contact hole SiO2

100 nm

Contact hole SiO2

MgO 100 nm MgO 100 nm

Size 100 × 100 nm

Result of R-H and I-V characteristics

• 1000
• 500

500 1000 400 600 800 1000 1200 1400

Resistance (Ω) H (Oe)

RA = 4.9 Ωµm2 MR = 167 %

b a c

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.0 0.2 0.4 0.6 0.8 1.0 1.2

P state AP state H_ext 118 Oe

Voltage (V) Current (mA)

a b c

a : P state c : 118 Oe b : AP state

Negative resistance appears in the voltage driven I-V characteristics under adequate external field!! Differential Resistance

• 700 Ω

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.0 0.2 0.4 0.6 0.8 1.0 1.2

. . 1 . 2 . 3 . 4 . 5 . 6 . 7 . . 4 . 8 1 . 2 1 . 6

Current (mA) Voltage (V)

P state AP state H_ext 118 Oe

Voltage (V) Current (mA) ↑↑ ↑↓

Current control Voltage control

Summary

“Giant Tunneling magneto resistance effect” is available. Making low resistance MTJs, Spin-transfer magnetization switching is possible. G-TMR offers large RF output. Voltage control of the MTJ revealed “Negative resistance nature” of the MTJs and gives an ability of amplification to MgO-MTJs. Highly nonlinear interaction between electron transport and spin orientation provides interesting functions for MTJs.

Spin-transfer Giant-TMR effect

Spin-polarized current Precession/ Switching

Voltage induced magnetization switching using perpendicularly magnetized material at room temperature

A Maruyama, Y. S., et al., Nature Nano, (2008)

Au(001)

Fe alloy(001) 3ML

MgO(001) Polyimide ITO