Vilquin Gautier

download Vilquin Gautier

of 21

  • date post

    14-Apr-2018
  • Category

    Documents

  • view

    224
  • download

    0

Embed Size (px)

Transcript of Vilquin Gautier

  • 7/30/2019 Vilquin Gautier

    1/21

    1

    FCMN, Albany (NY), USA B. Vilquin, B. GautierMay 13th, 2009

    Scaling Effects on Ferro-Electrics: Application

    in Nanoelectronics and Characterization

    Bertrand Vilquin & Brice GAUTIER

    Lyon Institute of Nanotechnologies

    Universit de Lyon

  • 7/30/2019 Vilquin Gautier

    2/21

    2

    FCMN, Albany (NY), USA B. Vilquin, B. GautierMay 13th, 2009

    Ferroelectrics: dielectrics crystals which a spontaneous electricpolarization due to atomic deplacement in the crystal structure

    The direction of polarization can be reoriented by an external electricl field:

    => domains where the spontaneous polarization is parallel

    => hysteresis loops

    Introduction: ferroelectricity

    Direction polarization can be used tostore information: memories

    Bit 0: Pr- 2 atomic stable positions

    in the crystal field

    Bit 1: Pr+

    => Non volatile data storage device

  • 7/30/2019 Vilquin Gautier

    3/21

    3

    FCMN, Albany (NY), USA B. Vilquin, B. GautierMay 13th, 2009

    At nano-scale, strong influence of the surface energy, depolarization field, etc.

    => Modification of polarization, dielectric constant, Curie temperature, etc.

    Nano-ferroelectric: properties

    E. Erdem et al.,

    J. Phys.: Condens.

    Matter 18, 3861

    (2006)

    What is the critical thickness to observe ferroelectricity in thin films?

  • 7/30/2019 Vilquin Gautier

    4/21

    4

    FCMN, Albany (NY), USA B. Vilquin, B. GautierMay 13th, 2009

    Nano-ferroelectric: still ferroelectric?

    Glinchuk M.D., Morozovska A.N., Eliseev E.A., J. Appl. Phys. 99, 114102 (2006)

    Triscone's group (Geneva): measurement of ferroelectricity down to 2.4 nm

    (PZT film) at room temperature.

    Deformation of the film due to mismatch between the parameters of the filmand substrate Um = (b a)/b (a, b are their lattice constants) induce built-inelectric field.

    => This field lead to electret state in thinner film.

    0 5 10 15 20 25 30

    0

    200

    400

    600

    800

    1000

    Film thickness h (lattice constants)

    Temp

    eratureT(K)

    Electret

    Self-polarizedferroelectric phase

    0 100 200 300 400 500

    1.03

    1.04

    1.05

    1.06

    1.07

    Film thickness h (A0)

    Tetragonality

    c/a

    Um=0

    Um

  • 7/30/2019 Vilquin Gautier

    5/21

    5

    FCMN, Albany (NY), USA B. Vilquin, B. GautierMay 13th, 2009

    Recent effort to predict properties of nano-ferroelectricsusing ab initio modelsGroups of Vanderbilt, Resta, Krakauer, etc.

    Nano-ferroelectric: new properties

    Polarization vortex in ferroelectricABO3

    dots by Virtual CrystalApproximation (VCA)Bellaiche, PRL 97 (2006)

    However new properties absent in bulk materials appear in nano-ferroelectrics.

    Superlattices of SrTiO3

    and PbTiO3

    => Unususal polarization behaviour,modification of T

    C...

    Dawber, PRL 95 (2005)

  • 7/30/2019 Vilquin Gautier

    6/21

    6

    FCMN, Albany (NY), USA B. Vilquin, B. GautierMay 13th, 2009

    Ferroelectric Radoom Access Memories: similar to DRAM but with aferroelectric layer instead of a dielectric layer

    Non volatile memories: data storage through

    the remnant polarization

    Commercial production already at 350 nm (Fujitsu)

    and 130 nm (Texas Instrument)

    Nano-ferro devices: FeRAM

    32 Mb SAMSUNG FeRAM

    Same functionnality as Flash

    Memories but:

    Lower power usage

    Faster write performance

    Greater maximum of cycles

  • 7/30/2019 Vilquin Gautier

    7/21

    7

    FCMN, Albany (NY), USA B. Vilquin, B. GautierMay 13th, 2009

    Ferroelectric Field Effect Transistor: similar to MOSFET, the gate oxide is aferroelectric

    Depending on remnant polarization, electrons are depleted or accumulated

    Non volatile memories

    Decrease ofstand-by loss ( vampire power )

    Only few perovskite oxides (big class of ferroelectric materials) are suitable forgrowth on silicon

    Nano-ferro devices: FeFET

  • 7/30/2019 Vilquin Gautier

    8/21

    8

    FCMN, Albany (NY), USA B. Vilquin, B. GautierMay 13th, 2009

    From 2D film to 1D dots:

    Focused Ion Beam etching, e-beam lithography, imprint

    High-precision positioning

    Size control but limited in resolution

    Damage the nano-structures (layer ~10 nm)

    Time-consuming

    Nano-fabrication: Top-down

    M. Alexe, Appl. Phys. Lett. 75, 1999

  • 7/30/2019 Vilquin Gautier

    9/21

    9

    FCMN, Albany (NY), USA B. Vilquin, B. GautierMay 13th, 2009

    Self-assembled process:

    Formation of arrays of ferroelectric nano-crystals on a substrate

    As for semi-conductor quantum dots growth, balance between interface,

    substrate and film energies

    Avoid the processing damage duringFIB patterning

    Smaller dimensions structures thanthose obtained with top-down processes

    Nano-fabrication: Bottom-up

    PbTiO3

    grown on SrTiO3

    withdifferent crystallineorientationsNomura, Appl. Phys. Lett. 86, 2005

    Nano-wires fabrication:

    Hydro-thermal decomposition ofbimetallic precursorWell-isolated single-crystalline BaTiO3 rods

    with diameters from 5 to 60 nm

    and several m-longPark, Adv. Mat. 15, 2003

  • 7/30/2019 Vilquin Gautier

    10/21

    10

    FCMN, Albany (NY), USA B. Vilquin, B. GautierMay 13th, 2009

    The AFM as a tool for electric characterization at the nanoscale :

    A conductive tip can => a nanometric electrode

    Piezoelectric motion controller => positioning with a nanometric resolution

    Examples : Electric Force Microscopy (EFM : electric field)

    Kelvin Force Microscopy (KFM : potential)

    Nanoscale characterization: AFM

    Characterization of the electrical properties of thedielectrics and ferroelectrics:

    Current measurements

    Capacitive measurements

    Piezoelectric measurements

  • 7/30/2019 Vilquin Gautier

    11/21

    11

    FCMN, Albany (NY), USA B. Vilquin, B. GautierMay 13th, 2009

    Piezoresponse Force Microscopy

    The reduction of the size of devices

    using ferroelectric layers is achallenging problem forcharacterization

    Characterization provides crucial feed

    back to growers

    Numerous size effects are expected in ferroelectrics materials :

    Coercive voltages

    Remnant polarisation

    Dielectric constant

    Smallest domain size ?

    Smallest thickness allowing ferroelectricity ?

    Piezoelectric constants

    Ferroelectric

    polarisation

    Ferroelectricmemory

    gate

    Must be measured at the nanoscale

    P

    x

    y

    z

  • 7/30/2019 Vilquin Gautier

    12/21

    12

    FCMN, Albany (NY), USA B. Vilquin, B. GautierMay 13th, 2009

    PFM: principle

    Thin ferroelectric film

    Bottom electrode

    Substrate

    PhotodiodeLaser

    Lock in amplifier

    REF

    AMPLITUDE x PHASE

    180 0

    f

    P

    P

    Antiparallel domains vibrate with an opposite phase

    Inverse piezoelectric effect => vibration of the surface due to the application of analternating voltage.

    All ferroelectrics are piezoelectric

    Topography + verticalpiezoelectric vibration (very

    weak compared to topography)

  • 7/30/2019 Vilquin Gautier

    13/21

    13

    FCMN, Albany (NY), USA B. Vilquin, B. GautierMay 13th, 2009

    Quasi 3-D mapping of domains

    Mapping of ferroelectric domains(component perpendicular to thesurface) in LiNbO3. The spatialresolution is nanometric.

    B. Gautier, V. Bornand, Thin Solid Films 515(4-

    5):1592, 2006

    P

    zx

    y

    z

    Pin-plane

    out of-plane The in-plane

    component in the y-direction is alsoaccessible

    The in-plane componentparallel to the cantilever (xdirection) remains inaccessible

  • 7/30/2019 Vilquin Gautier

    14/21

    14

    FCMN, Albany (NY), USA B. Vilquin, B. GautierMay 13th, 2009

    Quasi 3-D mapping of domains

    Mapping of ferroelectric domains(component perpendicular to thesurface) in LiNbO3. The spatialresolution is nanometric.

    in-plane

    out of-plane The in-plane

    component in the y-direction is alsoaccessible

    z

    P P

    P

    zx

    y

    The in-plane componentparallel to the cantilever (xdirection) remains inaccessible

  • 7/30/2019 Vilquin Gautier

    15/21

    15

    FCMN, Albany (NY), USA B. Vilquin, B. GautierMay 13th, 2009

    Creation of domains

    Creation of any polarisation patternApplications for the Surface Acoustic Waves Devices (SAW)

    => replacement of the top electrodes

    f ~VR

    T

    => 20 GhzT= 200 nm

    C. Thiebaud, D. Charraut, B. Gautier, J.C.Labrune, Ann. Chim. ScL Mat, 26:145 (2001)

    Local switchingof the polarisation by applying asufficient voltage between thetip and the sample (here 10 V)

    S. Ballandras, B. Gautier, D. Hauden and J.-C. Labrune.Patent USA Canada - Europe 0009246, 2001.

  • 7/30/2019 Vilquin Gautier

    16/21

    16

    FCMN, Albany (NY), USA B. Vilquin, B. GautierMay 13th, 2009

    Applications for ferroelectric memories

    Evolution of the domain size with the durationof the voltage pulse

    B. Gautier, C. Soyer, E. Cattan, D. Remiens and J.-C. LabruneIntegrated Ferroelectrics 269:219, 2002

    P. Paruch et al. Appl. Phys. Lett., Vol.

    79, No. 4, 23 (2001)

    Microstructure of the film, voltage amplitude,duration, geometry... influence the final size of thedomain => density of integration