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

JST-DFG workshop on Nanoelectronics, 21.23.01.2009 in Kyoto Spin-transfer related phenomena in magnetic tunnel junctions - Interplay of the giant tunneling magneto-resistance and spin-torque effect - Yoshishige Suzuki 1,2 Acknowledgements H. Maehara 3 , A. Deac 1, 2,* , T. Maruyama 1 , Y. Shiota 1 , T. Nozaki 1 , H. Kubota 2 , A. Fukushima 2 , S. Yuasa 2 , K. Tsunekawa 3 , D. D. Djayaprawira 1, 3 , and N. Watanabe 3 1 Osaka University, Graduate School of Engineering Science, Osaka, Japan 2 NanoElectronics Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan 3 Electron 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 o n i c s N-pole charge spin : electron charge : electron -e is a small manget brings electricity rotation (spin) S-pole S e m i c o n d u c t o r M a g n e t i s m （s p i n ） （c h a r g e ） e l e c t r o n i c s S p i n t r o n i c s

① GMR/TMR (Giant magneto-resistance / Tunneling magneto-resistance) Magetization → Conduction - - + + 0 0 MgO-Mangetic tunnel junction Yuasa / Parkin 2004 AlO-Mangetic tunnel junction Miyazaki / Moodera 1995 GMR Grünberg / Fert 1988

Development of Magnetic Tunnel Junctions 600 MgO (001) MR (%) at RT barrier Tohoku AIST[2] 400 Tohoku Tohoku Anelva-AIST Al-O IBM 200 AIST[1] barrier IBM Sony AIST Nancy Tohoku Fujitsu Tohoku MIT IBM NVE CNRS 0 MPI ‘95 ‘00 ‘05 ‘10 Year Al-O barrier MTJ MgO(001) barrier MTJ Fe(001) MgO(001) Fe(001) A. C. C. Yu, et al., JJAP 40, 5058 (2001) [1] S. Yuasa, Y. S. et al, Nature Materials , 3(2004)868.

Spintronics & Spin-transfer phenomena ① GMR/TMR (Giant magneto-resistance / Tunneling magneto-resistance) Magetization → Conduction ② Spin-injection magnetization switching Conduction → Magetization

② Spin-injection magnetization switching Conduction → Magetization ＋ ＋ － － Switching (MgO TMR) Kubota / Huai / Hayakawa 2005 Current induced Spin-transfer switching (GMR) domain wall motion Myers Yamaguchi, Ono/Vernier 1999 Tatara and Kohno Spin-transfer theory 2004 Slonczweski / Berger 1996

Spin-transfer model Conduction electrons (s ) are scattered by Local moments ( d ) Spin conservation in the s-d interaction d Reduction of S s s = Increase of S d Exchange scattering s FM1 FM2 Spin Torque Spin polarizer S1 s d s ∑ ∑ > 0 = 0 s s S 1 S 2 s s current

② Spin-injection ③ Spin-transfer oscillation magnetization switching d.c. current → RF oscillation Conduction → Magetization G M R : C o 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 ) G M R : C o r n e l l U n i v e r s i t y , N a t u r e ( 2 0 0 3 ) M g OM T J : A I S T , J J A P ( 2 0 0 5 ) P e r p . M T J : T o s h i b a , A P S m e e t i n g ( 2 0 0 8 ) H i g h p o w e r o 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 o n A N E L V A H i g h s p e e d s w i t c h i n g ( 2 0 0 p s e c ) , A . D e a c , Y . S . e t a l . , N a t u r e P h y s . ( 2 0 0 8 ) A . T u l a p u r k a r , Y . S . , e t a l . , A P L ( 2 0 0 5 )

Spintronics & Spin-transfer phenomena ① GMR/TMR ③ Spin-transfer oscillation (Giant magneto-resistance / d.c. current → RF oscillation Tunneling magneto-resistance) Magetization → Conduction ② Spin-injection ④ Spin-torque diode RF current → d.c. voltage magnetization switching Conduction → Magetization A. Tulapurkar, Y. S., et al .,(TMR) Nature , 438(2005)339. J. C. Sankey et al .,(GMR) Phys. Rev. Lett ., 96(2006)227601

Spin-torque diode effect 0 - + V - + Current Source Current Source 0 0 - + - + Curernt Curernt V V - + (B) No current : Shape anisotropy (C) Down to up current (A) Up to down current prefers makes magnetization anti-parallel makes magnetization parallel vertical alignment and resistance large. and resistance small. Thus it produces Thus it produces large positive voltage. small negative voltage. A. Tulapurkar, Y. S., et al., Nature, 438(2005)339

Voltage dependece of the spin-toruqes V c : AP->P Charge current and switching Spin current Spin-transfer torque Conductanc e : = + ∆ θ / cos I V G G 0 0 Torquance : = θ Torque / V T sin 0 J. C. Slonczewski, PRB (2005 ) H. Kubota, Y. S., et al. Nature Phys. (2007 )

Canon ANELVA Negative resistance and amplification H. Maehara in MgO-MTJs 実験

5 th 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 NM FM Esaki diode MR devices 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.” V I T Load resistance : R L R T < 0 ∆ V V V ∆ = < R L 0 L R ∆ I ∆ V V V in o ( ) ( ) + = + ∆ + ⋅ + ∆ ∆ I V V V I I R I I V 0 in T 0 L 0 o > V R = = L L 1 Gain ( ) + V R R in T L < 0 V Negative resistance region Amplification! We must realize the negative resistance in I-V characteristics.

C a s e o f o s c i l l a t i o n C a s e o f o s c i l l a t i o n Resistance = low state Small angle oscillation Large angle oscillation Free I AF AF AF External field I I c V AP state P state

Sample structure and deposition method � Equipment : “Canon ANELVA C-7100” Capping layer � Sputtering method : DC magnetron sputtering 1400 CoFeB (2 nm) for metals Resistance ( Ω ) MgO (1.12 nm) 1200 RF magnetron sputtering RF magnetron sputtering CoFeB (3 nm) for MgO with Ta paste for MgO with Ta paste 1000 Ru (0.85 nm) process ∗ process ∗ CoFe (2.5 nm) 800 ~ 10 -9 Torr � Base pressure : RA = 4.9 Ωµ m 2 AF layer 360 ℃ / 2h / 8 kOe � Anneal condition : 600 MR = 167 % Bottom electrode � Free layer : 2 nm 400 MgO sub. -1000 -500 0 500 1000 H (Oe) Sample structure We obtained high MR ratio at low resistance ∗ N. Nagamine, et al., APL

Micro fabrication 1) Patterning with EB lithography, Ion milling processes Junction area Junction area Bottom lead pad Bottom lead pad Size Resist Resist 100 × 100 nm 100 nm 100 nm Sub Sub Bottom electrode Bottom electrode 2) SiO 2 deposition and lift off processes Contact hole Contact hole Contact Contact SiO 2 SiO 2 SiO 2 SiO 2 hole hole 100 nm 100 nm SiO 2 SiO 2 3) Electrode pad formation and measurement Upper electrode Upper electrode 100 nm 100 nm MgO MgO Bottom electrode Bottom electrode

Result of R-H and I-V characteristics 1.2 1400 a : P state P state a AP state b : AP state Resistance ( Ω ) 1.0 H_ext 118 Oe c : 118 Oe 1200 Current (mA) b 0.8 Differential Resistance 1000 c - 700 Ω 0.6 c a 800 0.4 RA = 4.9 Ωµ m 2 600 b 0.2 MR = 167 % 400 0.0 -1000 -500 0 500 1000 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Voltage (V) H (Oe) Negative resistance appears in the voltage driven I-V characteristics under adequate external field!!

1.2 Voltage control 1 . 6 Current control ↑↑ 1 . 2 Current (mA) 1.0 Current (mA) 0 . 8 0 . 4 0.8 ↑↓ 0 . 0 0 . 0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 0 . 6 0 . 7 Voltage (V) 0.6 0.4 P state 0.2 AP state H_ext 118 Oe 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Voltage (V)

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-polarized current Spin-transfer Giant-TMR effect Precession/ Switching

Voltage induced magnetization switching using perpendicularly magnetized material at room temperature A ITO Polyimide MgO(001) 0 Fe alloy(001) 3ML Au(001) Maruyama, Y. S., et al. , Nature Nano, (2008)