+ All Categories
Home > Documents > MRAM 2 DIENY.pdf

MRAM 2 DIENY.pdf

Date post: 10-Feb-2018
Category:
Author: gokaran-shukla
View: 218 times
Download: 0 times
Share this document with a friend
Embed Size (px)

of 25

Transcript
  • 7/22/2019 MRAM 2 DIENY.pdf

    1/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Part 2: Spin Transfer Torque RAM

    (STTRAM)

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    In-plane magnetized STTRAM

    Reliability issues in STTRAM

    Out-of-plane magnetized STTRAM

    Downsize scalability of STTRAM

    Part 2: Spin Transfer Torque MRAM

    OUTLINE

  • 7/22/2019 MRAM 2 DIENY.pdf

    2/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Thermally Assisted (TAS) STT-TAS

    Hx

    Hy

    Field-driven STT (STT MRAM)

    Perpendicular

    Precessional

    DW motion

    Planar

    Spin-orbit torque

    (spin-Hall, Rashba)

    Several families of MRAM

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Current through cell proportional to MTJ area

    jwrite SST in-plane ~ 8.105A/cm quasistatic

    ~ 3.106A/cm @10ns

    STT MRAM scalability of write current

    Writing 0 Writing 1

    +

    = K

    M

    P

    te

    jSF

    planeinWR 22

    22

    0

    h

    Huai et al, Appl.phys.Lett.87, 222510 (2005) ;

    Hayakawa, Jap.Journ.Appl.Phys.44 (2005) L1246

    ONjSTT

    Vdd

    0

    freepinned

    ONjSTT

    0

    Vdd

    Writing determined by a current density :

    Field written

  • 7/22/2019 MRAM 2 DIENY.pdf

    3/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    STT MRAM Write influence of current pulse width

    Thermally activatedSTT switching

    PrecessionalSTT switching

    In-plane magnetized MTJ

    Hosomi et al, Sony, 4Kbit demo (2005)

    In the thermally activated regime:

    Ic0= extrapolated STT switching current at 1ns pulse width

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Courtesy Grandis

    STT MRAM compact cell

    Vertical transistor technology may allow even smaller cell

    Below 45nm, transistor does not limit cell size

  • 7/22/2019 MRAM 2 DIENY.pdf

    4/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    STT MRAM Distribution consideration

    ~1.4-1.8V~0.4-0.7V~0.15-0.2V

    70

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    STT MRAM Key parameters

    (thermal stability factor) data retention, read disturb, operating temperature range,downsize scalability

    ( should be between 60 and 80 depending on chip density)

    TMR (read signal) read speed, sense margin, tolerance on RA dispersion

    TMR above 150% to achieve fast (sub 10ns) read-out.

    Jc0 (write current density) cell size, write speed, write consumption, reliability

    J c below 1.106A/cm are desirable to insure select transistor size smaller than MTJ

    Vbd (MTJ breakdown voltage) reliability, endurance

    Vbd should be above 3 times write voltage (typically Vbd~1.5V at 10ns and Vwrite~0.5V)

    Key challenge is to achieve low write current and good retention at the sametime

  • 7/22/2019 MRAM 2 DIENY.pdf

    5/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    RETENTIONWRITABILITY

    Write current (in-plane MTJ):

    Thermal stability factor (in-plane magnetized MTJ)

    (A=area, =STT efficiencyHd=demag field=0Ms)=dampingMs=magnetizationtF=thickness of storage layer

    assuming shape anisotropy dominates

    Classical dilemma in memory technology :

    STT MRAM Key parameters

    Increasing the retention at small size requires to increase Ms and or tF but penaltyon write current.Importance to play on parameters such as Gilbert damping .

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Important parameters to reduce Jswitching :

    -Gilbert damping as low as possible (NiFe, CoFeB ~0.007-0.01)

    -Magnetization Ms as low as possible(Co75Fe25 Ms=1600emu/cm3, Co: Ms=1400emu/cm3, CoFeB: Ms~600emu/cm3,But must remain compatible with sufficient thermal stability factor

    -Thickness of the switching layer as small as possibleBut not too small because TMR amplitude degrades when magnetic electrode thinner than~1.5nm and Gilbert damping increases

    -Current polarization as large as possible (bccCoFe/MgO ~80%)

    - Dual stacks with two antisymmetric pinned layers

    - Increase perpendicular anisotropy in the storage layer

    Reducing current density for switching with in-plane magnetized MTJ

  • 7/22/2019 MRAM 2 DIENY.pdf

    6/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Gilbert Damping

    Insulators: Yttrium iron garnet

    1x10-4Gilbert damping Material

    Y3Fe5O12

    Semi metals: Heusler alloy

    2x10-3Gilbert damping Material

    NiMnSb

    Metals:

    0.01Co0.9

    Fe0.1

    0.007Ni0.8Fe0.2

    0.10-0.15(Co/Pd) ML

    0.2-0.3

    Gilbert damping Material

    (Co/Pt)

    Out-of-planeanisotropy butlarge damping

    Take advantage of the interfacial anisotropy at magnetic metal/oxide interface

    Mostcommonly

    used (CoFeB)

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Concept later used by Grandis

    Dual MTJ

    In-plane STT RAM: Dual stack with antiparallel pinned layers

    MTJ with partial

    out-of-plane

    anisotropy

    Proposed by SPINTEC in 2001: FR2832542 filed 16th Nov.2001, US6385082

    Lower RA

    higher RA

  • 7/22/2019 MRAM 2 DIENY.pdf

    7/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    In-plane STT RAM: In-plane magnetized MTJ with

    partial out-of-plane anisotropy in the storage layer

    Idea: Hd and Hk of opposite sign, Hd tends to bring back the magnetization in-planewhereas Hk tends to pull it out-of-plane

    PinnedReference

    layer

    Storagelayer bcc

    Fcc bilayer withPerpendicular

    anisotropy

    Pd/Co

    Ta 0.2nm structuraltransition layer

    CoFeB 2nm

    MgO

    CoFeB 3nmRu 0.7

    CoFe 2nm

    IrMn 7nm

    However, concern with thermalstability at sub-45nm dimension

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    2013: STT RAM product

  • 7/22/2019 MRAM 2 DIENY.pdf

    8/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Summary for in-plane STTRAM

    STT RAM development based on major breakthrough discoveries:-Giant TMR of MgO based MTJ-Spin transfer torque phenomenon

    Giant TMR of MgO based MTJ relies on spin-filtering of electrons according tothe symmetry of their wave functions. Requires very good bcc crystallinity ofboth the MgO barrier and adjacent CoFe magnetic layers.

    Low STT write current implies low Gilbert damping, low magnetization (at thecost of reduced thermal stability with in-plane shape anisotropy), high currentpolarization.

    Toggle MRAM good for robust, low density NVM applications (automotive,spatial)

    Inplane STT RAM: difficulty to achieve good retention and low write current atthe same time. Nevertheless some routes exist to reach dimensions ~ 40nm usingdual stack or structures with partial out of plane anisotropy.

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    In-plane magnetized STTRAM

    Reliability issues in STTRAM

    Out-of-plane magnetized STTRAM

    Downsize scalability of STTRAM

    Part 2: Spin Transfer Torque MRAM

    OUTLINE

  • 7/22/2019 MRAM 2 DIENY.pdf

    9/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Example of cross-

    sectional TEM viewof MgO MTJ

    TMR = 130 %R.A = 30.mMgO barrier: 1.1nm

    1.1nm

    V

    E ~ 5 108

    V/m

    Typical EBreakdown inoxides ~ 109V/m

    ~0.5V

    STTRAM endurance

    At each write event, the tunnel barrier is exposed to an electrical stress. How manycycles can it resist before electrical breakdown?

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Reliability of the tunnel barrier - endurance

    t variable

    30ns30ns

    Vapplied= 1.25V

    t =70nsExample:

    Application of repeated pulses of voltage across the barrier until breakdown occurs

    Accelerated conditions:

    1.2Volt

  • 7/22/2019 MRAM 2 DIENY.pdf

    10/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    =

    ttF exp1)(

    Cumulative distribution of deadMTJ after N pulse of duration spacedby t follows a Weibull distribution:

    with t=N and function oft

    =30ns=30nst =70nsVapplied=1.3V

    : Nb of cycles after which 1-1/e=63% of junctions have experienced breakdown

    Extremely long endurance can be obtained in MTJ under specific working conditions.Different tunneling regime compared to standard CMOS working conditions

    (thinner oxide, lower voltage, direct tunneling versus Fowler-Nordheimtunneling)

    Reliability of the tunnel barrier - endurance

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    STT RAM endurance

  • 7/22/2019 MRAM 2 DIENY.pdf

    11/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Dramatic increase in endurance to breakdown for an intermediate delay time ~80ns.Understood in terms of trapping/detrappingof electrons on traps inside the MgObarrier with escape~80ns and stress induced by electrostatic forces between trappedelectrons and electrodes

    Nbofcyclesto63%

    bre

    akdown

    Pulses ofsame polarity

    Pulses ofalternating polarity

    30ns30ns

    n

    po

    n Large number of electrons trapped inthe barrier (no time to escape). Large steadystress on the barrier.

    p At each pulse, some electrons gettrapped but then escape betweenpulses. Alternating stress on the barrier.

    oBalance between trapping anddetrapping:Moderate trapped charge and moderatetime-modulation of trapped charge

    Reliability of the tunnel barrier - endurance

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    -- - -+ + + +

    MgO

    Need to minimize density of trapping sites in MgO:

    Oxygen vacancies in MgO Interfacial traps at BO/MgO interface if formation of BO. Dislocations in MgO due to lattice mismatch between MgO and CoFe (~4%)

    Trapped electrons

    CoFeB

    CoFeB

    Screening charges appearing in the metallic electrodes

    Large stress generated on the barrier

    Selma Amara, Applied Physics Letters 99 (2011) 083501

    Reliability of the tunnel barrier - endurance

  • 7/22/2019 MRAM 2 DIENY.pdf

    12/25

  • 7/22/2019 MRAM 2 DIENY.pdf

    13/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Reliability of the tunnel barrier endurance

    Dislocations as possible electron trapping sites

    Possibility of improvement with ~10%V addition in CoFeB

    06.4a287.2a FeFe ==Possibility to reduce the

    crystallographic mismatch and

    thereby the density of

    dislocations by some V alloying21.4aMgO =

    38.4a210.3a VV ==

    TMR(%)

    Hoogefac

    tor(amplitudeof1/fnoise)

    Herranz et al,

    Appl. Phys. Lett. 96, 202501 (2010)

    1/f noise measurement may become

    a technique for characterizing the

    endurance of MTJ without stressingthem

    Optimum magnetic electrode composition: Co18Fe54V8B20)

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    In-plane magnetized STTRAM

    Reliability issues in STTRAM

    Out-of-plane magnetized STTRAM

    Downsize scalability of STTRAM

    Part 2: Spin Transfer Torque MRAM

    OUTLINE

  • 7/22/2019 MRAM 2 DIENY.pdf

    14/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Thermally Assisted (TAS) STT-TAS

    Hx

    Hy

    Field-driven STT (STT MRAM)

    Perpendicular

    Precessional

    Planar

    Several families of MRAM

    DW motion

    Spin-orbit torque

    (spin-Hall, Rashba)

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    +

    =Tk

    VM

    pAg

    Tkej

    B

    sBc

    planein

    2

    )0(

    4

    h

    In-plane versus out-of-plane STT switching

    In-plane magnetized MTJ Out-of-plane magnetized MTJ

    Thermal stability determined by in-

    plane anisotropy (shape anisotropy)Simpler materials but additional penaltyin jc due to out-of plane precession

    More complex materials but lower jcexpected thanks to direct proportionalitybetween J c and thermal stability

    =pAg

    Tkej Bc

    perp

    )0(

    4

    h

    = damping

    P = polarization

    A = Area

    g(0)~1

  • 7/22/2019 MRAM 2 DIENY.pdf

    15/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    STT switching in perpendicular MTJ

    TbFeCo

    TbFeCoCoFeB

    CoFeBMgO

    TMR = 10%, jc(30ns) = 5 106A/cm, (d=130nm) = 107

    Toshiba (2008):

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    A key point for p-STT MRAM is to be able to increase

    the perpendicular anisotropy without increasing the Gilbert damping

    Difficulty:Large anisotropy often implies large spin-orbit coupling (provided for instance by

    Pt, Pd, Au) which yields large Gilbert damping .

    In p-MTJ , current for switching by STT (Ic) proportional to Gilbert damping and tothermal stability factor

    Material issue in perpendicular STT-MRAM

    ( )Tk

    VMK

    B

    s 2/2

    0

    =

    Solution found thanks to the existence of a large perpendicular anisotropy

    at magnetic metal/oxide interface

    =pAg

    Tkej Bc

    perp

    )0(

    4

    h

    = damping

    P = polarization

    A = Area

    g(0)~1

  • 7/22/2019 MRAM 2 DIENY.pdf

    16/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Surprisingly large perpendicular anisotropy at magnetic metal/oxide interface(Monso et al APL 2002)

    S.Monso, et al, APL 80 (2002), 4157-9. First observation of PMA at Co/AlOx

    B.Rodmacq et al,Journ.Appl.Phys.93, (2003), 7513. PMA at Co or CoFe/MgO, CrO, TaO

    A.Manchon et al, Journ. Appl. Phys. 104, 043914 (2008). XPS, XAS, interpretation of PMA at M/Ox

    B.Rodmacq et al, Phys.Rev.B79, 024423 (2009) Influence of annealing on PMA at Co/AlOxL.Nistor et a, IEEE Trans Mag., 46 (2010), 1412 Correlation PMA -TMR at CoFe(B)/MgO

    Very general phenomenon ofperpendicular anisotropy observed at awide variety of M/Ox interfaces withM=Co, CoFe, CoFeBand Ox= AlOx, MgO, TaOx, CrO2,

    Due to hybridizationbetween Co dz andO sp orbitals

    Co-dz

    O-pz

    Perpendicular Magnetic Anisotropy (PMA)

    at magnetic metal/oxide interface

    -0.2

    -0.1

    0

    0.1

    0.2

    -8 -6 -4 -2 0 2 4 6 8

    Mz

    Out-of-plane magnetic field (kOe)

    3'30

    1'30

    3'002'302'00

    Time of exposureto oxygen plasma

    -0.8 -0.4 0 0.4 0.8

    (T)

    Underlayer/Co/Al

    z

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    1 3

    2

    CoFe

    buffer/CoFe 1/Mg_x natural oxidation/Ru 5 (nm) Ta=330C

    Ta=330Cbuffer/CoFe 1.6/Mg x natural oxidation/CoFe 2.5/Ru 0.8/NiFe 5/IrMn 10 (nm)

    Very good correlation between max TMR and max PMA (tMg=1.2 nm)

    PMA at magnetic metal/oxide interface

    Correlation PMA energy TMR amplitude

    Interfacial anisotropy energy atCoFe/MgO interfaceKs~1.5erg/cm=1.5mJ /mas large as at Co/Pt interfacedespite weak spin-orbitcoupling in Co, Fe, Mg, O

  • 7/22/2019 MRAM 2 DIENY.pdf

    17/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Explanation of the correlation between PMA & TMR

    Co(Fe)-O interfacial bond formation influences both TMR amplitude and PMA

    Co

    O

    Optimumoxidation

    hybridization between O sp orbitals andCo dz2 orbital combined with spin-orbitinteraction yields the interfacial PMA[A. Manchon et al., J.Appl.Phys. 104, 043914, 2008]

    TMR ofCo/MgO/Co MTJ

    TMRPMA

    Mg

    O

    Co

    O

    Mg

    Co

    >

    [Butler et al.,, J.Lee e t a l . Poster EV09 IntermagMMM 2010]

    Perpendicular underlayer/Co/MgO

    Better penetration of1 electronsthrough the barrier if O terminated

    TMR TMR

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    PMA at magnetic metal/oxide interface

    Confirmation by ab-initio calculations

    Ks=2.93 10-3J /m for two Fe/MgO interfacesi.e. 1.46 10-3J /m per Fe/MgO interfaceLower for under or over-oxidized interface

    H.Yang, M.Chshiev, B.Dieny, Phys.Rev.B 2011.

  • 7/22/2019 MRAM 2 DIENY.pdf

    18/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Ikeda et al, Nat.Mat.2804 (2010)

    TMR=124%RA=18.m

    =43(70 required for 1Gbit)

    P-MTJ based on interfacial PMA (i-PMA)

    No Pt nor Pd in the stack

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Perpendicular STT Demo Chips

    Toshiba 64 Mb perpendicular STT

    K.Tsuchida et al.ISSCC 2010

  • 7/22/2019 MRAM 2 DIENY.pdf

    19/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    50ns

    10ns

    253 cells

    Perpendicular STT Demo Chips

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Thermal stability in p-MTJ

    Two possible magnetization reversal mechanisms

    1) Coherent rotation (preferred at small dimensions)

    2) Nucleation of a reversed domain at pillar edge and propagation of domainwall across the pillar (preferred at larger dimensions)

    In between Curlingmode as described by A.Aharoni

    Domain wall width comparable to pillar diameter

    The chosen switching mechanism will be the one with lowest energy barrier

  • 7/22/2019 MRAM 2 DIENY.pdf

    20/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Thermal stability factor in p-MTJ

    Thermal stability factor essentially determined by effective anisotropy and reversal

    volume which can be limited to the nucleation volume if nucleation/propagation reversal:

    Si-sub/Ta(5)/Ru(10)/Ta(5)/Co20Fe60B20(0.9)/MgO(0.9-1.0)/Co20Fe60B20(1.5)/Ta(5)/Ru(5)

    Sato el al, Tohoku, Hitachi, Intermag 2011, CC04

    Required for32Mbit

    Dnucleation~45nm

    J c MTJ area nucleation area

    Coherent

    rotation

    Nucleation-propagation

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Thermal stability factor in p-MTJ

    To favor coherent rotation rather than nucleation at edges and propagation ofdomain wall, it is preferable:

    -To use magnetic material with large stiffness constant i.e. high Curie temperaturesuch as Co rich CoFe alloys (Tcurie Co~1400K whereas Tcurie Fe~1043K)

    -To use material with low magnetization(weaker demagnetizing field at edges of the pillar

    -To avoid strond reduction of stiffness constantat the edges of the pillar due to etching damages B

  • 7/22/2019 MRAM 2 DIENY.pdf

    21/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    In-plane magnetized STTRAM

    Reliability issues in STTRAM

    Out-of-plane magnetized STTRAM

    Downsize scalability of STTRAM

    Part 2: Spin Transfer Torque MRAM

    OUTLINE

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    How small can we go with p-STT MRAM?

    1) From magnetic point of view

    MgO

    MgO

    or

    Reference layer

    Additional polarizing layer toincrease STT efficiency(US6950335B2, Fig.8 (2001)) andcompensate stray field fromreference layer

    RA~2-5.m (provides the TMR)

    RA70

    Magnetic stack optimization:

  • 7/22/2019 MRAM 2 DIENY.pdf

    22/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    K.Yakushiji et al, APL97, 232508(2010)

    Optimal structure: (Co/Pt) or (Co/Pd) ordered ML

    for reference and additional polarizing layers

    Post-annealing stability of up to 370 C, provide a very large PMA Ku~ 39.106 ergs/cm3

    .

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    = .)0(

    4Tk

    Pg

    eI B

    perp

    write

    h

    The total current to write by STT is related to the thermal stability factor by

    For 1Gbit chip, 1 FIT in 10years withproba

  • 7/22/2019 MRAM 2 DIENY.pdf

    23/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    IEDM2011, paper24.1Sub-20nm STT MRAM

    65nm

    40nm

    20nm

    17nm

    There is a clearly improved process B (?)

    Ta/Co20Fe60B20/MgO/pinned ref

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Asymmetry likely due to stray field from reference layer

    Distribution from dot to dot not reported

    Ic=45A for size 22nm

    IEDM2011, paper24.1Sub-20nm STT MRAM

  • 7/22/2019 MRAM 2 DIENY.pdf

    24/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Edge damages due to etching : IBE

    Etching of the MTJ pillar can have mainly electrical impacts but also magnetic impacts

    IBE : Avoid redepositionof metallicspecies on the side of the barrier.

    Amorphizationof MgO may take placeat edges locally changing RA and TMR(may be cured by post-etchinganneals)

    Tapering can affect the magneticproperties (not a strong effect)

    Alloying at edges may affect anisotropy

    and exchange stiffness (a reduction by2 orders of magnitude of exchangestiffness is acceptable).

    MgO

    Ta

    Ta

    PtMn

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    Post etching anneal may help curing the damages at edges. Encapsulation required.Need to recrystallize the barrier and neighboring electrodes around the edges andrestaure the strong interfacial anisotropy, the right RA and TMR amplitude.

    Post-etching annealing

    Fe or Fe rich CoFeB

    Ti/Ta

    Fe or Fe rich CoFeBMgO

    Co60Fe10Cr10B

    MgO

    Co10Fe70B

    (Co2/Pd2) ML

    Ti/Ta

    Co10Fe70BTi/Ta

    (Co2/Pd2) ML

    46264

    152

    40

    15

    2

    40

    Co60Fe10Cr10BThanks to the insertion betweentwo MgO barriers, should bequite thermally stable uponannealing

    Proposed structure should withstand high annealing at least up to T ~370C:

    K.Yakushiji et al, APL97, 232508(2010)Withstand annealing T of 370C

    K.Yakushiji et al, APL97, 232508(2010)Withstand annealing T of 370C

  • 7/22/2019 MRAM 2 DIENY.pdf

    25/25

    [email protected] J uly 2013 Part 2 inMRAMinMRAM2013

    100nmMTJ pillar etched by RIE

    Edge damages due to etching : RIE

    Still under development.See tutorial on MRAM processing (JP Nozieres) .

    Main issues:Avoid corrosion of the magnetic materialsVarious types of materials requiring different etchgas chemistry

    Conclusion on p-STT RAM

    In p-MTJ s, taking advantage of the interfacial anisotropy at CoFe/MgOinterface allows to circumvent the issue of combining large PMA with lowGilbert damping.

    Switching by coherent rotation below 25nm diameter MTJ pillar.

    Optimal structure is a double barrier MTJ with oppositely magnetizedpolarizing layers and a multilayered structure of the storage layer.

    Can be scaled down to 10nm diameter from magnetic and electricalviewpoints.

    Edge damages produced by etching must be carefully addressed.Significant progresses lately according to Samsungs report at IEDM

    2011.


Recommended