Ferroelectric materials for piezoelectric, pyroelectric, and

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Ferroelectric materials for piezoelectric, pyroelectric, and memory applications

Marin AlexeMax Planck Institute of Microstructure PhysicsHalle – Germany

Outline

Introduction Basics of Ferroelectricity– Applications– Definitions

Ferroelectric materials for– Piezoelectric applications– Non-volatile memories– Pyroelectric applications *

Electrical characterization Nanoscale ferroelectrics

* With the kind contribution of Paul Muralt, EPFL, Lausanne CH

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Outline

Textbook– Ferroelectric crystals, F. Jona and G. Shirane, Pergamon, Oxford 1962– Physical properties of crystals, J. F. Nye, Clarendon, Oxford, 1964– Principles and Applications of Ferroelectric Crystals …, M.E. Lines and A.M. Glass,

Clarendon, Oxford 1977– Ferroelectric memories, J. F. Scott, Berlin, Springer, 2000– Ferroelectric devices, K. Uchino, Dekker, 2000– Nanoelectronics and Information Technology, R. Waser (ed). Wiley-VCH, 2003

Edited books– Thin film ferroelectric materials and devices, R. Ramesh (ed.), Kluwer, 1997– Ferroelectric thin films : synthesis and basic properties, Paz de Araujo, Scott, and Taylor,

Gordon and Breach, 1996– Nanoscale phenomena in ferroelectric thin films, S. Hong (ed), Kluwer, 2004– Nanoscale characterisation of ferroelectric materials : scanning probe microscopy

approach, Alexe and Gruverman (eds), Springer, 2004Databases

– Landolt-Börnstein, vol. 16, Ferroelectric and related substances, ed. E. Nakamura, Springer, 1981

Review papers– The physics of ferroelectric ceramic thin films for memory applications, J.F. Scott,

Ferroelectrics Review 1, 1 (1998)– Ferroelectric, dielectric and piezoelectric properties of ferroelectric thin films and

ceramics, D. Damianovici, Rep. Prog. Phys. (61)1267 (1998)– Physics of thin-film ferroelectric oxides, M. Dawber et al., Rev Mod. Phys., in press– M. Fiebig, Revival of the magnetoelectric effect, J. Phys. D, 38 (2005) R123 – etc.

Basics of Ferroelectrics

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Applications

The physics of ferroelectric memories, Auciello O, Scott JF, Ramesh R., Physics Today 51, p22, July 1998

Applications

Piezoelectric Sensors/Actuators, MEMS

Pyroelectric Detectors/Sensors

Electro-optical switches and modulators

Optical Waveguides

Dynamic RAMs (capacitors)

Tunable Microwave Devices

Non-Volatile RAMs (memory)

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Basics of ferroelectricity

Piezolectrics:– Charge generation by mechanical fields

Pyroelectrics:– Charge generation by thermal fields

Ferroelectrics:– Charge generation by electrical fields

Applications-What are they good for?

And converse !

Basics of …

What are they good for?Piezoelectrics– Mechanical strain (stress) ⇔ Electric field (charge)

Stress X

+Q

-Q

P

D= deffX

Di= dijkXjk

D – charge densitydeff – effective piezoelectric coeff.X – stress

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Basics of … Piezoelectric Sensors

Basics of … Piezoelectrics

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Basics of … Piezoelectric Actuators

Basics of …

What are they good for?Pyroelectrics– Thermal variation ⇔ Charge generation

∆T

+Q

-Q

P

∆Q=p∆T

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Basics of … Pyroelectrics – Intruder alarms

absorption layer black Pt

top electrode Cr/Au

pyroelectric film PbTiO3 (PT)

membrane Si3N4/SiO2

SiO2

Design layout (large geometry)

Si

exaggerated vertical scale1 mm

1 mm

Pyroelectric thin film detector packaged into a TO-39 housing

30 m max.

Ferroelectrics– Switching by electrical field ⇔ Charge generation

Basics of …

P

E

P-E Characteristics (hysteresis loop)

What are they good for?

∆Q=2Pr

-4 -2 0 2 4

-100

-50

0

50

100

Pola

rizat

ion

(µC

/cm

2 )

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Ferroelectrics – Switching

Basics of …

Ferroelectric Non-volatile Memories

Ferroelectrics – Switching

Basics of …

Ferroelectric Non-volatile Memories

Smart-card – Smart-tags: Non-contact (radio-powered) micro controller and memory

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Definitions

Ferroelectrics are dielectric materials with permanent dielectric polarization which is switchable with an applied external field

Dielectrics

Piezoelectrics

Pyroelectrics

FerroelectricsFerroelectrics

Ferroelectricity – symmetry-based phenomenon

Electrostrictive32 classes

No symmetry centre21 classes

Piezoelectric20 classes

Non-piezoelectric1 class

Pyroelectric10 classes

Non-Pyroelectric10 class

symmetry centre11 classes

Ferroelectric

Ion shift in the perovkite cell

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Ferroelectric Materials (BaTiO3)

ParaelectricCubic

Ferro ITetragonal

Ferro IIOrthorhombic

Ferro IIRhombohedral

Ferroelectric Materials (BaTiO3)

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Ferroelectric materials

Ferroelectric Materials

Main ferroelectric oxides

Pb-based materials - Pb(Zr,Ti)O3 , PbTiO3Layered perovkites – SrBi2Ta2O9, Bi4Ti3O12BaTiO3-based materials – (Ba,Sr)TiO3LiNbO3, LiTaO3 – Niobate familyBiFeO3 – MultiferroicsEtc.

There are >500 ferroelectric compounds (without solid-solutions)– Landolt-Bornstein, Ferro- and Antiferroelectric Substances, Springer, 1975

For most demanding applications only oxides are really considered

Choosing the optimum material is an applicationChoosing the optimum material is an application--dependent dependent problemproblem

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Materials for ferroelectric memories


Useful property: charge by switching

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Ferroelectric materials for piezoelectric applications

Ferroelectric materials for piezoelectrics

Direct piezoelectric effect:D= deffX

Converse piezoelectric effect

x= deffE

D – charge densitydeff – effective piezoelectric coeff.X – stressx - strain

Material property: piezoelectric coefficient (third-rank tensor, dijk)

Electrostrictive effect – quadratic effect, present for all materials

xij=QijklPkPl

Di= dijk Xjk

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Ferroelectric materials for piezoelectrics

Relation between piezoelectric coefficient and polarization:

dim=εikQmikPk

For particular case of tetragonal symmetry:

d33=2ε33Q33P3d31=2ε33Q13P3d15=2ε11Q44P3

ε - dielectric permittivitym –index in the matrix notation

Relationship between dzz an Pz

PZTtetragonal

BaTiO3

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PZTrhombohedral

Ferroelectric materials for piezoelectric appl.

Figures of merit:

x=dEE=gX

d – actuator figure of meritg – sensor figure of merit

For polycrystalline materials depends on the sample symmetry:

Pd33

d31

Electromechanical coupling factor k

k2=Stored mechanical (electrical) energy/Stored electrical (mechanical) energy

g=d/ε

k2=d2/(εs) s – elastic stiffness

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Ferroelectric materials for piezoelectric appl. Maximum d in systems with morphotropic phase boundary (MPB)

Pb(Zr,Ti)O3

Du et al., APL 72, 2421(1998)Single-crystal d-values

Damianovici,Rep.Prog.Phys.Ceramic d-values

6 possible orientations8 possible orientations

Ferroelectric materials for piezoelectric appl. Monoclinic phase at MPB

Noheda et al, Phys. Rev. B, 63 (2000) 014103

- not a sharp boundary between tetragonal and rhombohedral phases

-An additional monoclinic phase might exists

-There are three different phases with similar free energies and the polarizationcan rotate easily among different directions*

* Fu and Cohen, Nature 403 (2000) 281

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Ferroelectric materials for piezoelectric appl. MPB are present in many systems:

Pb(Zn1/3Nb2/3)O3-PbTiO3 – PZN-PT Pb(Mg1/3Nb2/3)O3-PbTiO3 – PMN-PT

Ferroelectric materials for piezoelectric appl. Lead-free materials (K0.5Na0.5)1-xLix)(Nb1-yTay)O3

Saito et al., Nature 432 (2004) 84

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Nanoscale characterization

Nanoscale measurements

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PFM- Out-of-plane detection

Poling, biasingEDC > EC

Probing, imagingEAC << EC

Detection

PFM – In-plane detection

L.M. Eng, M. Abplanalp, and P. Günter, Appl. Phys. A 66, S679 (1998).

∆x

Ez

)sgn(~ 15 xPEdx∆

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PZT(20/80; 150 nm)/SRO/STO

400nm400nm

PFM- domain imaging

Correlation of dzz with polarization

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Interpretation of the Piezoresponse Signal

Piezoelectric coefficient for single-crystal mono-domain ferroelectrics with a centrosymmetric paraelectric phase:

3441115

3133331

3333333

222

S

S

S

PQdPQdPQd

εεε

=

=

=

for other cases effective values may apply:

zSzzzzzz PQd ε2=

PSPS

Interpretation of the Piezoresponse Signal

Randomly oriented grains – polycrystalline films

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Calculations were made for PZT (30/70) using data from: M.J. Haun, E. Furman, S.J. Jang, and L.E. Cross, Ferroelectr. 99, 13 (1989).

θθθθ 333

21531 coscossin)()( ddddzz ++=

[001

] (pm

/V)

[010](pm/V)

(pm/V)

(pm

/V)

(pm/V)

The piezoelectric “surface” for PZT

PSPS

Effect of the orientation on hysteresis

dzz NOT directly proportional to Pz !

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C. Harnagea, A. Pignolet, M. Alexe, and D. Hesse, Integrated Ferroelectrics (2004)


Rhombohedral PZT Bi3Ti4O12

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Pyroelectrics


Intruder alarm

absorption layer black Pt

top electrode Cr/Au

pyroelectric film PbTiO 3 (PT)

membrane Si3N4/SiO 2

SiO2

Design layout (large geometry)

Si

exaggerated vertical scale1 mm

1 mm

Pyroelectric thin film detector packaged into a TO-39 housing

30 m max. Bell 1994, Kohli 1997

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Working thin film focal plane array for thermal imaging

ROIC

PYROEL.

mirror

semi-transparent top electrodes

transparent bottom electrode

metal plug

Cortesy Raytheon Infrared Imaging Systems

NETD about 100 mK in 2004.Hansen and Beratan et al., 2000-2004

SignalContact

BottomElectrode

Ferroelectric

TopElectrode

CommonContact

ROIC

(Cross S

(Raytheon)

PbTiO3 based thin films deposited on silicon substrates

Substitutions by:

Zr (PZT)La (PLT)Ca (PCT)

p – pyroelectric coefficient

Figure of merit

ε/p∝

Relative dielectric constant

Pyro

elec

tric

coef

ficie

nt (

Cm

-2K

-1)

300

100

200

400

500

600

0100 200 300 400 500 6000

PT

15/85 25/75 30/70

10

PZT

15

PLT

20

10

10

PCT20/80

p

ε0 100 200 300 400 500

0.3

0.4

0.5

0.6

PbTiO3

TC=490oC

Spon

tane

ous

Pola

rizat

ion

(C/m

2 )

Temperature [oC]

TE

TP

TDp S

E ∂∂

+∂∂

=⎟⎠⎞

⎜⎝⎛

∂∂

=ε

ε – dielectric constant at the working frequency (1Hz)

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Electro-optic materials



Electrooptic (and acoustooptic) effects are of considerable practical importance as they can be used to:

– modulate (amplitude and phase) light beams

– shift the light frequency

– alter the direction in which the beam travels

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Likewise of piezoelectric effect there is:– Linear EO effect (Pockels)

• Non-centrosymmetric crystals– quadratic EO effect (Kerr)

• centrosymmetric crystals

By applying an electric field the anisotropy changesThe optical indicatrix changes in both value (refractive index) and direction


1111111 2

62

2

52

2

42

2

32

2

22

2

12 =⎟

⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛ yz

nxz

nxy

nz

ny

nx

n

Optical indicatrix

By applying an electric field E=(Ex,Ey,Ez) the optical coefficients are linearly changing

Linear (Pockels) effect

r is the tensor of EO coefficients (similar to piezo coeff)is in the range of 10-12 m/V

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Electro-optic materialsConsidering the contribution of the converse piezoelectric effect

Sj is a component of the strain; pij is the elastooptic tensor.

low f high f (Pockel’s)

Electro-optic materialsLongitudinal EO modulation (KDP)

Vπ is the voltage necessary toproduce a retardation of π

Transversal EO modulation (LiNbO3)

light

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Photorefractive materials



Photorefractive materials are electroopticmaterials which exhibit also a high internal photovoltaic effect. They can be used to:

– Holographic storage

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5 mm

LiNbO3:Fe

less Fe2+ more Fe2+

K. Buse et al., Phys. Rev. B 56, 1225 (1997)

CB

VB

hν

Fe 2+ Fe 3+

Photorefractive materials LiNbO3:Fe

)(32 CondBandeFehFe +↔+ ++ ν

iijjj Ernn 3

21

=∆

Photorefractive materialsHolographic storage

J. Ashley, IBM J. RES. DEVELOP. VOL. 44 NO. 3 MAY 2000

write read

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J. Ashley, IBM J. RES. DEVELOP. VOL. 44 NO. 3 MAY 2000

Basic holographic data storage system

II. Nanoscale ferroelectrics

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Fabrication of nanosize ferroelectrics


Nanosize Nanosize ferroelectric ferroelectric structuresstructures

Lithography Lithography methodsmethods

d>50 nmd>50 nm

SelfSelf--assembly assembly methodsmethods

d<50 nmd<50 nm

Vapor Vapor depositiondeposition

CSDCSD

MOCVDMOCVD

ee--beambeam

imprintimprint

??

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Lithography

Maskless patterning methods

Ion-beam milling

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(a)

(b)

(c) (d)

(e) (f)

Ion milling Ion milling -- Ramesh et al. Univ. of MarylandRamesh et al. Univ. of Maryland

Fabrication of nanosize ferroelectricsIon beam millingIon beam milling

NagarajanNagarajan et al.et al.Nature Mat. 2, 43 (2003)Nature Mat. 2, 43 (2003)

1 µm

with awith a--domainsdomains no ano a--domainsdomains

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Ferroelectric characterizationSize effects Size effects -- ion milled PZT structuresion milled PZT structures

Nagarajan et al., Nature Materials 2, pp43, 2003

E-beam lithography

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Fabrication: e-beam direct writing

1. Metalorganic layer 1. Metalorganic layer depositiondeposition

2. E2. E--beam exposurebeam exposure

4. Crystallization4. Crystallization3. Developing 3. Developing


Patterned test structure

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Annealed 650°CAnnealed 650°C

NonNon--annealedannealed


“Large area” uniform patterning

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Ferroelectric characterizationSFM switching of PZT cellsSFM switching of PZT cells

0.50.5 µµm cellsm cells

Ferroelectric characterizationSize effects and polarization imprintSize effects and polarization imprint

0 200 400 600 800 1000-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

Offs

et

Cell size (nm)

ββ δδ

β=(34±3.7) nmδ=(7.5±4.5) nm

12121

12121

2

2

+⎟⎠⎞

⎜⎝⎛ −⎟

⎠⎞

⎜⎝⎛ −

−⎟⎠⎞

⎜⎝⎛ −⎟

⎠⎞

⎜⎝⎛ −

=Ω

hd

hdδβ

δβ

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Imprint lithography

Fabrication methodsFerroelectric nanostructures by imprint lithography

Harnagea et al. APL, Sept. 1 2003

PZT structures on PZT structures on SrTiOSrTiO33:Nb:Nb

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Array of 300 nm PZT structuresArray of 300 nm PZT structures6 x 6 µm6 x 6 µm

Imprint lithography

C. Harnagea, Mater. Res. Soc. Symp. Proc. 748, U.4.2.1. (2003).

Soft lithography

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Soft lithographyMicro Contact Printing Micro Molding

George Whitesides at Harvard

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Nanosize ferroelectrics fabricated by self-assembly methods

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Latex monolayer as mask

Ma et al., Appl. Phys. Lett. 83, 3770 (2003)Ma et al., Appl. Phys. Lett. 83, 3770 (2003)

Self-assembly methods

Island growth mode of MOCVDIsland growth mode of MOCVDM. Shimizu et al.M. Shimizu et al.

Tune the growth conditions to Tune the growth conditions to achieve island growth mode, achieve island growth mode, which allows fabrication of which allows fabrication of nanoscale islands nanoscale islands

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Towards single FE grains on the nano scale

T. Schneller, A. Roelofs, RWTH Aachen, ISIF 2000

ApproachSeparation of grains bynon-continuous CSD films

FE film: PbTiO3Route: APP, 0.3 m, 4 coatings, 750 C

R. Waser, et al. Integrated Ferroelectrics, Vol. 36, pp. 3-20 (2001).

A. Seifert, A. Vojta, J.S. Speck, F.F. Lange, J. Mater. Res. 11 (1996) 1470.

Ferroelectric nano-crystals by self-assembly

Microstructural instability in epitaxial ultraMicrostructural instability in epitaxial ultra--thin CSDthin CSD--deposited films deposited films

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Nanosize ferroelectrics by self-assembly

selfself--assembled PZT structures obtained by CSDassembled PZT structures obtained by CSD

X-ray diffraction pattern

10 20 30 40 50 60 70 80

Inte

nsity

(a. u

.)

2θ (deg.)

100

STO

300

STO20

0S

TO

300

PZT

200

PZT

100

PZT

200

STO

, Kβ

300

STO

, Kβ

Structural investigations - XRD

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Annealing temperature

Nanosize ferroelectrics by self-patterning

800oC 950oC 1100oC

1-D ferroelectric systems

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Nanowires

Ferroelectric nanowires

H. Park, Harvard UniversityNanoletters 2, 447 (2002)

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Ferroelectric nanowires

H. Park, Harvard UniversityH. Park, Harvard UniversityNanolettersNanoletters 2, 447 (2002)2, 447 (2002)

Nano-shell tubes

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Piezoelectric nano-shell tubesHigh aspect ratio

Si templateLuo et al. APL 83, 440 (2003)

Ferroelectric nano-tubes

•• Material: PZT & BTOMaterial: PZT & BTO•• Diameter 0.5 to 2 Diameter 0.5 to 2 µµmm•• Wall thickness 20Wall thickness 20--30 nm30 nm•• Length 100Length 100--200 200 µµmm

WaferWafer--scale tube arraysscale tube arrays

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Piezoelectric nano-shell tubes

-10 -8 -6 -4 -2 0 2 4 6 8 10-100

-80-60-40-20

020406080

100

2nd measurement 1st measurement

d 33(p

m/V

)

Voltage(V)


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100 1000 100000.1

1

10

0.1

1

10

Si absorbtion

Wav

elen

gth

(µm

)

lattice constant (nm)

Si Al2O3

Mater. Res. Soc. Symp. Proc. 748, U.4.2.1. (2003).

Ferroelectric nano-tubes4’’ wafer4’’ wafer

Ferroelectric materials for piezoelectric, pyroelectric, and

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