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  • Nanoscale resistive switchingdevices based on metal oxides

    Jacopo FrascaroliSupervisor Prof. Alberto PulliaCo-Supervisor Dr. Sabina Spiga

  • Jacopo Frascaroli Milano, October 15th 2013

    Outline

    Resistive switching:

    phenomenology and applications

    Device characterization

    Nano devices using block copolymers

    Pt

    TiN

    ALD - HfO2

    5 - 6 nm

    40 m

    40 m

  • Jacopo Frascaroli Milano, October 15th 2013

    Resistive switching in MIM structures

    AMetal

    Metal

    Insulator

    Capacitor-like structure with electrically alterable resistivity

    A large variety of insulating materials shows resistive switching properties:

    Transition metal oxides (TMO) metal doped perovskites Polymers ...

  • Jacopo Frascaroli Milano, October 15th 2013

    Switching behavior

    Applying a proper potential difference at the two electrodes, the device resistance changes

    Reset

    Set

  • Jacopo Frascaroli Milano, October 15th 2013

    Resistive switching mechanism in TMO

    The anion motion leads to a valence change of the metal sublattice (cations) R change

    Filamentary type

    R. Waser, Adv. Mater. 2009 and ref. therein; A. Sawa, Materials Today 2008

    Mobile species:Oxygen ions oxygen vacancies

    Initial state Forming

    Reset Set

  • Jacopo Frascaroli Milano, October 15th 2013

    Very simple structure Highly scalable CMOS process compatibility Low switching time Low power consumption

    Crossbar array

    Resistive switching applications

    Memory

    Need for a lithographictechnology to enable cell scaling

    Si nanocrystal

    NAND-Flash (FG)

    Techn.node F [nm]

    Cell size[F2]

    10

    20

    30

    40

    180 130 90 65 5x 3x

    NOR-Flash (FG/NROM)

    MRAM

    FeRAM

    PCM

    ReRAM ?3D stack

    2x4x 1x

    niche and niche and

    embedded embedded

    applicationsapplications

    codecode

    datadata

    evolutionaryevolutionary

    disruptivedisruptive

    3D-SONOS

    Spintronics

    NAND-Flash (FG)

    Techn.node F [nm]

    Cell size[F2]

    10

    20

    30

    40

    180 130 90 65 5x 3x

    NOR-Flash (FG/NROM)

    MRAM

    FeRAM

    PCM

    ReRAM ?3D stack

    2x4x 1x

    niche and niche and

    embedded embedded

    applicationsapplications

    codecode

    datadata

    evolutionaryevolutionary

    disruptivedisruptive

    3D-SONOS

    Spintronics

    MRAM-spin torque

  • Jacopo Frascaroli Milano, October 15th 2013

    Resistive switching applicationsLogic Artificial neural

    networks

    Yang, J. Joshua, Dmitri B. Strukov, and Duncan R. Stewart. "Memristive devices for computing" Nature nanotechnology 8.1 (2012)

  • Jacopo Frascaroli Milano, October 15th 2013

    Experimental results

    Up to 2000 reproducible switching cycles demonstrated

    Pt

    TiN

    ALD - HfO2

    5 - 6 nm

    40 m

    40 m

    Microscopic device characterization

    -2 -1 0 1 2

    -1.0

    -0.5

    0.0

    0.5

    1.0

    1.5

    2.0

    C

    urr

    ent

    (mA

    )

    Voltage (V)

    Reset

    Set

  • Jacopo Frascaroli Milano, October 15th 2013

    Possible to tune the low resistance varying the maximum allowed current

    during set (current compliance)

    0.1 110

    2

    103

    104

    RLO

    W (

    )

    Set max current (mA)

    Experimental resultsElectrical characterization

    -1.5 -1.0 -0.5 0.0

    -5

    -4

    -3

    -2

    -1

    0

    Curr

    ent

    (mA

    )

    Voltage (V)

  • Jacopo Frascaroli Milano, October 15th 2013

    1.0 1.5 2.0 2.5 3.0104

    105

    RH

    IGH

    (

    )

    Reset voltage (V)

    Possible to tune the high resistance varying the maximum reset voltage

    0 1 2 3

    0.0

    0.2

    0.4

    0.6

    0.8

    1.0

    Curr

    ent

    (mA

    )

    Voltage (V)

    Experimental resultsElectrical characterization

  • Jacopo Frascaroli Milano, October 15th 2013

    Two different retention behaviors

    Arrhenius dependence of the retention time on temperature

    100

    101

    102

    103

    104

    105

    106

    101

    102

    103

    104

    105

    106

    Low resistance stateR (

    )

    t (s)

    TiN/HfO2/Pt 150C

    Failure bit

    Typical bits

    High resistance state

    2.2 2.3 2.4 2.5 2.6 2.7 2.8

    1000/T (K-1)

    Ea

    HR = 1.5 +/- 0.1 eV

    180 160 140 120 100 80

    T (C)

    100

    101

    102

    103

    104

    105

    106

    (

    s)

    Experimental resultsRetention behavior

    Retention behavior at 150C

  • Jacopo Frascaroli Milano, October 15th 2013

    Slow retention loss Modification of the residual

    filament The TiOxNy /HfO2 interface

    may play a role

    Fast retention loss Very narrow gap.

    Diffusion of a few vacancies can reconstruct the conductive channel

    100

    101

    102

    103

    104

    105

    106

    101

    102

    103

    104

    105

    106

    Low resistance stateR (

    )

    t (s)

    TiN/HfO2/Pt 150C

    Failure bit

    Typical bits

    High resistance state

    Experimental resultsRetention modeling

    Pt

    TiN

    HfO

    x

    Oxigen speciesOxigen vacancies

    Forming

    -V

    Pt

    TiN

    HfO

    x

    Oxigen speciesOxigen vacancies

    Reset

    +V

    Set Reset

    J. Frascaroli et al., in preparation

  • Jacopo Frascaroli Milano, October 15th 2013

    Slow retention loss Modification of the residual

    filament The TiOxNy /HfO2 interface

    may play a role

    Fast retention loss Very narrow gap.

    Diffusion of a few vacancies can reconstruct the conductive channel

    100

    101

    102

    103

    104

    105

    106

    101

    102

    103

    104

    105

    106

    Low resistance stateR (

    )

    t (s)

    TiN/HfO2/Pt 150C

    Failure bit

    Typical bits

    High resistance state

    Experimental resultsRetention modeling

    Pt

    TiN

    HfO

    x

    Oxigen speciesOxigen vacancies

    Forming

    -V

    Pt

    TiN

    HfO

    x

    Oxigen speciesOxigen vacancies

    Reset

    +V

    Set Reset

    J. Frascaroli et al., in preparation

  • Jacopo Frascaroli Milano, October 15th 2013

    10-5

    10-4

    10-3

    102

    103

    104

    105

    RHI

    RLOW

    R (

    )

    Area (cm2)

    Filamentary conduction

    High scalability potential

    Experimental results

    No area dependence of the resistance

    Device area dependence

  • Jacopo Frascaroli Milano, October 15th 2013

    Previous works

    ReRAM nanoscaling

    Top-down

    B. Govoreanu et al. IEEE Electron DevicesMeeting (2011)

    Anodized-Aluminium Oxide templates

    Bottom-up

    D. Perego et al. Nanotechnology 24

    (2013)

    Electron beam lithography

    Slow and serial lithographic technique Limited number of devices Not compatible with actual

    technology

  • Jacopo Frascaroli Milano, October 15th 2013

    Block Copolymers

    Hexagonal cylinders template

    Experimental result: block copolymers self assembling of hafnium dioxide

  • Jacopo Frascaroli Milano, October 15th 2013

    GraphoepitaxyM. Perego et al. Nanotechnology 24, 8 (2013)

    Pre-patterned structures can be used to drive the self assembly of block copolymers Courtesy of F. Ferrarese Lupi, MDM IMM-CNR

  • Jacopo Frascaroli Milano, October 15th 2013

    Top electrode nano patterning

    Electrical measurements with c-AFM

    Combining directed self-assembling with electron beam lithography

    Lift-off process

  • Jacopo Frascaroli Milano, October 15th 2013

    Substrate: ALD HfO2

    MetalPhysical

    depositionThickness

    Tungsten (W) sputtering 5 nm

    Platinum (Pt)

    sputtering 5 nm

    ebeam 5 nm

    Lift-off process study

    Experimental result

  • Jacopo Frascaroli Milano, October 15th 2013

    200 nm

    We demonstrated the possibility to obtain nano scaled top Pt electrodes over

    large areas of HfO2

    Experimental result

  • Jacopo Frascaroli Milano, October 15th 2013

    Current activity

    Device characterization andstudy of the retention behavior

    Implementing the block copolymer self-assembling on HfO2

    Study of the lift-off process for top electrodes nano patterning

  • Jacopo Frascaroli Milano, October 15th 2013

    Future outlook

    Electrical characterization of the nano devices using C-AFM to inspect the physical properties at the nano scale

    Find alternative strategies for the fabrication of resistive switching devices using block copolymers self-assembly

  • Jacopo Frascaroli Milano, October 15th 2013

  • Jacopo Frascaroli Milano, October 15th 2013

    Initial state

    Fresh cell

    Resistive switching mechanismH. Akinaga and H. Shima, Proceedings of the IEEE 2010

  • Jacopo Frascaroli Milano, October 15th 2013

    Soft breakdown

    Initial state

    GND

    SET (forming)

    On state(Low resistance)

    Fresh cell Forming

    V+

    Resistive switching mechanism

  • Jacopo Frascaroli Milano, October 15th 2013

    V-

    GND

    Off state(High resistance)

    RESET

    Fresh cell Forming Reset

    On state(Low resistance)

    Resistive switching mechanism

  • Jacopo Frascaroli Milano, October 15th 2013