Tunnel Magnetoresistance Effect And Its Applications

Tunnel Magnetoresistance Effectand Its ApplicationsS. Yuasa, R. Matsumoto, A. Fukushima,H. Kubota, K. Yakushiji, T. Nakamura,Y. Suzuki and K. Ando

CollaboratorsOsaka University(High-frequency experiment)Canon Anelva Corp.(R & D of manufacturing technology)Toshiba Corp.(R & D of Spin-MRAM)Funding agencies

Outline(1) Introduction(2) Epitaxial MTJs with a crystalline MgO(001) barrier(3) CoFeB / MgO / CoFeB MTJs for device applications

ic recording・permanent magnetSince 1988LSISpintronicsBoth charge and spin ofthe electron is utilized fornovel functionalities.Hard Disk Drive(HDD)

What is “magnetoresistance” ?A change in resistance by an application of H.Magneto-Resistance ; MRResistance (R)Magnetoresistance ratio(MR ratio)Magnetic field H requiredto induce MR change0Magnetic field (H)MR ratio at RT & a low H ( 1 mT) is importantfor practical applications.

MagnetoresistanceMR ratio (RT & low H)Year1857AMR effectMR 1 2 %Lord KelvinGMR effectMR 5 15 %A. Fert, P. Grünberg(Nobel Prize 2007)198519901995200020052010TMR effectMR 20 70 %T. Miyazaki, J. Moodera

Tunnel magnetoresistance (TMR) effectFM electrodeTunnel barrierFM electrodeParallel (P) stateAntiparallel (AP) stateTunnel Resistance RP : lowTunnel Resistance RAP : highMagnetic tunnel junction (MTJ)MR ratio (RAP – RP) / RP (performance index)

Room-temperature TMR in 1995T. Miyazaki(Tohoku Univ.)J. S. Moodera(MIT)Ferromag.electrodeAmorphous Al-OFerromag.electrodeAl-O – based MTJMR ratios of 20 – 70% at RT

Technologies for HDD read headWrite headRecordingmediumMediumHeadSSNN SSSNNNNSRecording density （Gbit / 100 10 1 0.1 TMR headGMR head0.011990 1992 1994 1996 1998 2000 2002 2004 2006 2008YearRead headNext-generation readhead is indespensablefor 200 Gbit / inch2.

Magnetoresistive Random Access Memory (MRAM)MTJBit Line“0”Ward Line“1”Non-volatile memory

Magnetoresistive Random Access Memory (MRAM)Bit LineMTJWrite LineWord Linen pCMOSn Cross-section structureFreescale’s 4 Mbit-MRAMbased on Al-O MTJsVolume production since 2006. 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.

MR effectsMR ratio (RT & low H)Year1857AMR effectMR 1 2 %Device applicationsHDD headInductivehead1985GMR effectMR 5 15 %1990MR head1995TMR effectMR 20 70 %GMR head200020052010MemoryTMR headMRAMMuch higher MR ratios were requiredfor next-generation devices.

Outline(1) Introduction(2) Epitaxial MTJs with a crystalline MgO(001) barrier(3) CoFeB / MgO / CoFeB MTJs for device applications

Theoretical prediction of giant TMR effect in Fe/MgO/FeFe(001)MgO(001)Fe(001)Fully epitaxial MTJ First-principle calculations ・Butler et al., Phys. Rev. B 63, 056614 (2001).・Mathon & Umerski, Phys. Rev. B 63, 220403 (2001).MR ratio 1000%

Spin polarization PTunnelbarrier FM 2FM 1eeEnergyEnergyEFEnergyEFD1 D1 Tunnelbarrier FM 2FM 1D2 D2 Parallel (P) stateTunnel resistnce: RPMR (RAP – RP) / RP 2P1P2 / (1 – P1P2),EnergyEFD1 D1 EFD2 D2 Antiparallel (AP) stateTunnel resistnce: RAP( Dα ( EF ) Dα ( EF ) ),Pα ( Dα ( EF ) Dα ( EF ) )Spin polarization Pα 1, 2.

Tunneling process in MTJsAmorphous Al-O barrierCrystalline MgO(001) barrierNo symmetry4-fold 01)Various Bloch statestunnel incoherently.MR ratio 100% at RTΔ2’Δ5Δ1Δ1Δ1Only the Bloch states with Δ1symmetry tunnel dominantly.

Fully spin-polarized Δ1 band in bcc Fe(001)1.5Δ1 E - EF ( eV )1.0majority spinminority spin0.5Δ1 EF0.0-0.5Γ(001) directionHFully spin-polarized Δ1 band Giant MR ratio is theoretically expected.Not only bcc Fe but also many other bcc alloys basedon Fe or Co have fully spin-polarized Δ1 band.(e.g. bcc Fe1-xCox , Heusler alloys)

Fully epitaxial Fe/MgO/Fe MTJ grown by MBEFe(001)(Pinned layer)MgO(001)Fe(001)(Free layer)TEM imageS. Yuasa et al., Nature Materials 3, 868 (2004).2 nm

Magnetoresistance of epitaxial Fe/MgO/Fe MTJ300MR ratio ( % )tMgO 2.3 nm200T 20 KMR 247%T 293 KMR 180%1000-200-1000100200H ( Oe )MTJs with a single-crystal MgO(001) barrierS. Yuasa et al., Nature Materials 3, 868 (2004).

Magnetoresistance of textured MgO-based MTJMTJs with a (001)-oriented poly-crystal (textured) MgO barrierS. S. P. Parkin et al., Nature Materials 3, 862 (2004).

Up to 600% at RT260MR ratio (%) at RT240“Giant TMR effect”220200180Crystal MgO(001)tunnel barrier160IBM [3]AIST [2]140120100Amorphous Al-Otunnel barrier8060AIST [1]Nancy40CNRS-CSIC200199520002005Year[1] Yuasa, Jpn. J. Appl. Phys. 43, L558 (2004). [2] Parkin, Nature Mater. 3, 862 (2004).[3] Yuasa, Nature Mater. 3, 868 (2004).

Outline(1) Introduction(2) Epitaxial MTJs with a crystalline MgO(001) barrier(3) CoFeB / MgO / CoFeB MTJs for device applications

MgO(001)AmorphousCoFeB260MR ratio (%) at RT240Anelva - AIST [4]IBM [3]220MgO(001)FeCo(001)200Crystal MgO(001)tunnel barrier180160AIST [2]Textured MTJ140MgO(001)120Fe(001)100Amorphous Al-Otunnel barrier8060AIST [1]Fully epitaxialMTJNancy40CNRS-CSIC200199520002005Year[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).

MTJ structure for practical applicationsFor MRAM & HDD read headFree layerorTunnel barrierPinned layerRuFM (Co-Fe)This structure isbased on fcc (111).AF layer (Pt-Mn or Ir-Mn)for exchange biasingMgO(001) cannot be grown on fcc (111).4-fold symmetry3-fold symmetry

MTJ structure in as-grown stateCollaboration with sCoFeBTEM imageDjayaprawira, SY, Appl. Phys. Lett. 86, 092502 (2005). Ideal for device applicationsThis structure can be grown on any kind of underlayersby sputtering deposition at RT post - annealing.

CoFeB / MgO / CoFeB - MTJ with practical ree layerTunnel barrierPinned layerSyF structureAF layer forexchangebiasingStandard bottom structure for MRAM and HDD head

Crystallization of CoFeB by post - annealingS. Yuasa et al., Appl. Phys. Lett. 87, 242503 (2005).Amorphous CoFeBAnnealingabove 250 ºCbcc CoFeB(001)AmorphousCoFeBCrystal-Textured MgO(001)Textured MgO(001) lizationAmorphous CoFeBAmorphousbcc CoFeB(001)CoFeBAs-grown MTJCrystallization of CoFeBMgO(001) layer acts as a template to crystallize amorphous CoFeB.“Solid Phase Epitaxy”Because the Δ1 band in bcc CoFeB(001) is fully spin-polarized,CoFeB/MgO/CoFeB MTJs show the giant TMR effect.

Sputtering depositionCanon-ANELVAC-7100 systemφ 8 inchStandard sputtering machinein HDD industryThermally oxidizedSi wafer (8 or 12 inch)100 wafers a day !

Year1857Industrial applicationsMR effectsMR ratio (RT & low H)AMR effectMR 1 2 %HDD headInductivehead1985GMR effectMR 5 15 %1990MR head1995TMR effectMR 20 70 %GMR head20002005MemoryGiant TMR effectMR 200 600 %TMR headMRAMMgO-TMR head2010Spin-torqueMRAMNoveldevicesMicrowave, etc.

Technologies for HDD read headWrite headRecordingmediumMediumHeadSSNN SSSNNNNSRecording density （Gbit / 100 10 1 0.1 TMR headGMR head0.011990 1992 1994 1996 1998 2000 2002 2004 2006 2008YearRead headNext-generation readhead is indespensablefor 200 Gbit / inch2.

MgO-TMR head for ultrahigh-density HDDWafer of MgO-TMR headMgO-TMR headCutIntegrationIntegrationMagnetic shield(top lead)PermanentmagnetPermanentmagnetMgO–MTJ Commercialized in 2007. Density 250 Gbit / inch2 achieved. Applicable up to 1 Tbit / inch2.20 nmMagnetic shield(bottom lead)TEM image

Year1857Industrial applicationsMR effectsMR ratio (RT & low H)AMR effectMR 1 2 %HDD headInductivehead1985GMR effectMR 5 15 %1990MR head1995TMR effectMR 20 70 %GMR head20002005MemoryGiant TMR effectMR 200 600 %TMR headMRAMMgO-TMR head2010Spin-torqueMRAMNoveldevicesMicrowave, etc.

Spin-torque MRAM （SpinRAM）M. Hosomi et al.(Sony), Technical Digest of IEDM 2005, 19.1.MTJCoFeBMgOCoFeBRu1 nmCoFeCMOSWrite current density, JC0 2 x 106 A/cm2JC0 of 5 x 105 A/cm2 is required for Gbit-scale SpinRAM.

SpinRAM having perpendicular magnetizationT. Kishi (Toshiba), SY et al., IEDM (2008) 12.6.Upper metal50 nmMTJBottom elctrode50nmUpperelectrodeStorage layerMgOReference layerorMgO(001)A TEM image of 50 nm-sized MTJPerpendicularly-magnetizedelectrodesJC0 106 A/cm2 achieved !A CMOS integrated MTJ arrayPerpendicularly magnetized MTJis a promising technology forGbit-scale Spin-RAM.

Year1857MR effectsMR ratio (RT & low H)AMR effectMR 1 2 %Industrial applicationsHDD headInductivehead1985GMR effectMR 5 15 %::commercializedcommercialized1990MR head1995::perspectivesperspectivesTMR effectMR 20 70 %GMR head20002005MemoryGiant TMR effectMR 200 600 %TMR headMRAMMgO-TMR headNoveldevices2010Spin-RAMMicrowave, etc.

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