Spintronic components for memories, logic and RF applications OUTLINE Giant MagnetoResistance (GMR), Benefit in magnetic recording technology Tunnel Magnetoresistance (TMR) Spin-transfer Magnetic Random Access Memories (MRAM) Hybrid CMOS/MTJ components for non-volatile and reprogrammable logic Radio Frequency oscillators based on spin-transfer Conclusion ESM 2009 09/09/09 B.Dieny
Acknowledgements R.C. Sousa C.Papusoi J.Hérault M.Souza L.Nistor E.Gapihan S.Bandiera G.Prenat U.Ebels D.Houssamedine B.Rodmacq Lomonosov A.Vedyaev N.Ryzhanova University O. Redon Work partly supported by the projects M.C.Cyrille B.Delaet MAGLOG (IST-STREP-510993) SPINSWITCH (MRTN-CT-2006-035327) J.-P. Nozières MAGICO (ANR 2006) L. Prejbeanu CILOMAG (ANR 2007) V.Javerliac K.Mc Kay ESM 2009 09/09/09 B.Dieny
Development of spin-electronics: strong synergy between basic research and applications Fe/Cr multilayers A.Fert et al, PRL (1988); P.Grunberg et al, PRB (1989) R/R P ~80% at RT ~ 80% Magnetic field (kOe) Development of spintronics paved with breakthrough discoveries: -1) GMR Hard disk drives (1990-2004) -2) Tunnel MR MRAM, hard disk drives (1995 - … for HDD, 2006-… for MRAM) -3) Spin-transfer MRAM, RF oscillators ESM 2009 09/09/09 B.Dieny
Benefit of GMR in magnetic recording GMR spin-valve heads from 1998 to 2004 ESM 2009 09/09/09 B.Dieny
1) GMR in magnetic recording ESM 2009 09/09/09 B.Dieny
Dramatic increase in areal storage density over the past 50 years increase 8 10 ESM 2009 09/09/09 B.Dieny
1982 1982 2.5 m*10 m 2.5 m*10 m 1984 1984 Evolution of magnetic bit size in hard disk drives 1986 1986 ESM 2009 09/09/09 1.8 m*7 m 1.8 m*7 m 1988 1988 1990 1990 0.8 m*3.2 m 0.8 m*3.2 m 1992 1992 0.56 m*2.2 m 0.56 m*2.2 m 1994 1994 0.25 m*1 m 0.25 m*1 m 1996 1996 B.Dieny 80nm*310nm 80nm*310nm 1998 1998 2000 2000 50nm*200nm 50nm*200nm 50nm*150nm 50nm*150nm 2002 2002 40nm*140nm 40nm*140nm 2004 2004 40nm*120nm 40nm*120nm 2006 2006 35nm*100nm 35nm*100nm 2008 2008
Reduction in size and increase in capacity Areal storage density: +60%/year ESM 2009 09/09/09 B.Dieny
New applications of HDD made possible thanks to miniaturization GMR spin-valve heads from 1998 to 2004 ESM 2009 09/09/09 B.Dieny
2) Magnetic tunnel junctions Tunnel magnetoresistance at 300K in amorphous Alumina based MTJ: Julliere (1975) but at low T only Moodera et al, PRL (1995); Myazaki et al, JMMM(1995). Free layer: CoFe 4 nm Free layer: CoFe 4 nm Free layer: CoFe 4 nm Al 2 O 3 barrier 1.5nm Al 2 O 3 barrier 1.5nm or or Reference layer :CoFe Reference layer :CoFe Reference layer :CoFe TMR~40-70% 3nm 3nm 3nm IrMn 7nm IrMn 7nm IrMn 7nm « Giant » tunnel magnetoresistance at RT in crystalline MgO based MTJ: Parkin et al, Nature Mat. (2004); Yuasa et al, Nature Mat. (2004). TMR~200-500% ESM 2009 09/09/09 B.Dieny
Magnetic Tunnel Junctions (MTJ): a new path for CMOS/magnetic integration • Resistance of MTJ compatible with Mag resistance of passing FET (few k ) process • MTJ can be deposited in magnetic back end process • No CMOS contamination CMOS process • MTJ used as variable resistance controlled by field or current/voltage (Spin-transfer) Above CMOS technology Cross-section of Freescale 4Mbit MRAM based on field switching ESM 2009 09/09/09 B.Dieny
3) Spin-transfer Predicted by Slonczewski (JMMM.159, L1(1996)) and Berger (Phys.Rev.B54, 9359 (1996)), Giant or Tunnel magnetoresistance : Acting on electrical current via the magnetization orientation Spin transfer is the reciprocal effect : Acting on the magnetization via the spin polarized current ~1nm Co Cu Co M.D.Stiles et al, Phys.Rev.B.66, 014407 (2002) Polarizing layer Polarizing layer Free layer Free layer Conduction electron flow Conduction electron flow Reorientation of the direction of polarization of current via incoherent precession/relaxation of the electron spin around the local exchange field Torque on the Free layer magnetization ESM 2009 09/09/09 B.Dieny
Magnetization dynamics: Effective field + spin-torque Slonczewski (JMMM.159, L1(1996)) and Berger (Phys.Rev.B54, 9359 (1996)), Stiles, Levy, Fert, Barnas, Vedyaev Polarizer M dM dM M H bI . M aI . M M M M eff p p dt dt Spin-torque term: damping Gilbert Effective field term (conserve energy) (or antidamping) term Damping term ( Modified LLG) Non conservative a and b are coefficients proportional to the spin polarization of the current Precession from H Damping torque (intrinsic Gilbert damping ) effective field Current-induced torque M (Spin-torque) Effective field term seems weak in metallic pillars (<10% of spin-torque term) but more important in MTJ (~30% of spin-torque term) ESM 2009 09/09/09 B.Dieny
Energy dissipation and energy pumping due to spin transfer torque Without spin torque (standard LLG) : <0 Dissipation, leading to relaxation towards effective field Z.Li and S.Zhang, Phys.Rev.B68, 024404 (2003) With spin torque term : Large damping dE/dt can be either>0 or <0 With Large damping: standard dynamical behavior, Low damping With low damping: New dynamical effects such as spin current induced excitations ESM 2009 09/09/09 B.Dieny
Current induced switching: Macrospin approximation Initial orientation From J.Miltat Polarisation of spin-current Final orientation Three steps: -Increase in precession angle -switching in the opposite hemisphere -fast relaxation Analysis of stability of LLG equation : initial state becomes unstable for a 2 M H H 2 M J s K ext s crit Where a J is prefactor of ST term: g 1 J Switching of a 2.5nm Co layer B a P J for j~2-4.10 7 A/cm 2 2 2 d e M s ESM 2009 09/09/09 B.Dieny
Magnetization switching induced by a polarized current Katine et al, Phys.Rev.Lett.84, 3149 (2000) on Co/Cu/Co sandwiches (Jc ~2-4.107A/cm²) Field scan Current scan 9,1 9,1 9,1 9,1 H = -4 Oe H = -4 Oe I = -0.4 mA I = -0.4 mA I + 9 9 9 9 R(ohms) R(ohms) R(ohms) R(ohms) CoFeCu2 Cu 8,9 8,9 8,9 8,9 CoFeCu1 8,8 8,8 8,8 8,8 I - 8,7 8,7 8,7 8,7 -400 -400 -200 -200 0 0 200 200 400 400 -8 -8 -4 -4 0 0 4 4 8 8 H(Oe) H(Oe) I(mA) I(mA) j c P-AP =1.9.10 7 A/cm² j c AP-P =1.2.10 7 A/cm² By spin transfer, a spin-polarized current can be used to manipulate the magnetization of magnetic nanostructures instead of by magnetic field. Can be used as a new write scheme in MRAM Or to generate steady state oscillations leading to RF oscillators ESM 2009 09/09/09 B.Dieny
Spintronic components “1” “0” R low R high R(H) Write/read heads Memories Magnetic field sensors Freescale 4Mbit VDD VDD MP1 MP1 MP2 MP2 OUT - OUT - OUT+ OUT+ Cu J PtMn MN3 MN3 MN1 MN1 CoFe Al 2 O 3 MN2 MN2 CoFe Sen Sen (Pt/Co) BL0 BL0 BR0 BR0 Cu RF components Logic circuits ESM 2009 09/09/09 B.Dieny
Field induced magnetic switching (FIMS) MRAM Writing Principle : Store data by the direction (parallel or antiparallel) of Bit line magnetic layers in MTJ Non-volatile storage element: MTJ Transistor OFF Word line "1" Selectivity achieved by combination of two perpendicular magnetic fields Reading "0" Transistor ON ESM 2009 09/09/09 B.Dieny
Field induced switching MRAM Write Operation H hard Stoner-Wohlfarth switching • Selectivity based on Astroïd diagram • With proper adjustment of Hx and Hy, only the cell simultanously submitted to Hx and Hy switches, and not the half selected cell H easy • Requires narrow distributions of switching field manufacturing issues 4Mbit product from FREESCALE launched in 2006. Great achievement which demonstrates that CMOS/MTJ integration is possible in a manufacturable process. However, High power consumption as large magnetic fields (~50-70Oe) required for switching: I~5mA/Line. Freescale 4Mbit Power consumption will increase upon scaling down due to increasing shape anisotropy necessary for thermal stability. ESM 2009 09/09/09 B.Dieny
Poor scalability of field induced switching MRAM Limited scalability due to electromigration in bit/word lines F Transistor OFF ESM 2009 09/09/09 B.Dieny
Solution 1: Spin-Transfer Torque MRAM Slonczewski, Berger (1996); STT in MTJ: Huai et al, APL (2004); Fuchs et al, APL (2004) The bipolar current flowing through the MRAM cell is used to switch the magnetization of the storage layer. Reading at lower current density then writing so as to not perturb the written information while reading. Hayakawa et al, Japanese Journal of Applied Physics 44, (2005),L 1267 ESM 2009 09/09/09 B.Dieny
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