tutorial isif 2005
TRANSCRIPT
I. Ferroelectric materials for piezoelectric, pyroelectric, and memory applications II. Nanoscale ferroelectrics
ISIF-2005 Shanghai, April 17, 2005
Marin AlexeMax Planck Institute of Microstructure PhysicsHalle – Germany
Outline
Introduction Basics of FerroelectricityFerroelectric materials for– Piezoelectric applications– Non-volatile memories– Pyroelectric applications
Multi-ferroicsNanoscale ferroelectrics
Outline
Textbook– Ferroelectric crystals, F. Jona and G. Shirane, Pergamon, Oxford 1962– 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 this-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.
Introduction
Mark Twain
"There are three kinds of lies: lies, damned lies and statistics.“
Introduction
02000400060008000
10000120001400016000
1970-1975
1981-1985
1991-1995
2001-2005
Papers onFerroelectrics
INSPEC database
020000400006000080000
100000120000140000160000
1970-1975
1981-1985
1991-1995
2001-2005
Papers onSemiconductors
0
0,02
0,04
0,06
0,08
0,1
0,12
1970-1975
1981-1985
1991-1995
2001-2005
Ferro/Semicon
02468
101214161820
1970-1975
1981-1985
1991-1995
2001-2005
Nature & Science
Ferroelectrics
Basics of ferroelectricity
Piezolectrics:– Charge generation by mechanical fields
Pyroelectrics:– Charge generation by thermal fields
Ferroelectrics:– Charge generation by electrical fields
What are they good for?
And converse !
Basics of …
What are they good for?Piezoelectrics– Mechanical strain (stress) ⇔ Electric field (charge)
E
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
Basics of …
What are they good for?Pyroelectrics– Thermal variation ⇔ Charge generation
∆T
+Q
-Q
P
∆Q=p∆T
Ferroelectrics– Switching by electrical field ⇔ Charge generation
Basics of …
P
E -6 -4 -2 0 2 4 6
-60
-40
-20
0
20
40
60 P
V
P-E Characteristics (hysteresis loop)
What are they good for?
∆Q=2Pr
Applications
The physics of ferroelectric memories, Auciello O, Scott JF, Ramesh R., Physics Today 51, p22, July 1998
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
Ferroelectric Materials
Main ferroelectric oxides
Pb-based materials - Pb(Zr,Ti)O3
Layered perovkites – SrBi2Ta2O9, Bi4Ti3O12
BaTiO3-based materials – (Ba,Sr)TiO3
There are >500 ferroelectric compounds (without solid-solutions)– Landolt-Bornstein, Ferro- and Antiferroelectric Substances, Springer, 1975
For most demanding applications only oxides are seriously consideredChoosing the optimum material is an application-dependent problem
Ferroelectric Materials
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
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
Relationship between dzz an Pz
PZTrhombohedral
Ferroelectric materials for piezoelectrics
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
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
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
Pyroelectrics
by Paul Muralt, Swiss Federal Institute of TechnologyLausanne
PbTiO3 based thin films deposited on silicon substrates
Relative dielectric constant
Pyro
elec
tric
coef
ficie
nt (
Cm-
2 K-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
PCT
Substitutions by:
Zr (PZT)La (PLT)Ca (PCT)
Various literature data
20/80
Figure of merit
∝ p/ ε
p
ε
Intruder alarm
absorption layer black Pt
top electrode Cr/Au
pyroelectric film PbTiO 3 (PT)
membrane Si3N4/SiO2
SiO 2
Design layout (large geometry
Si
exaggerated vertical scale1 mm
1 mm
Pyroelectric thin film detectorpackaged into a TO-39 housing
30 m max. Bell 1994, Kohli 1997
IR MicrosystemsSwitzerland
Linear pyroelectric arraysApplication in infrared gas spectroscopy
Willing, Kohli, Muralt et. al. 1995-1999Willing. Kohli, SeifertSince 2000
MINAST
grating
lamp
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 SystemsNETD about 100 mK in 2004.
Hansen and Beratan et al., 2000-2004
SignalContact
BottomElectrode
Ferroelectric
TopElectrode
CommonContact
ROIC
(Cross S
(Raytheon)
Ferroelectric Materials
Materials for ferroelectric memories
Ferroelectric Materials
Useful property: charge by switching
Ferroelectric Materials
Intrinsic requirements– Polarization ↑– Switching speed ↑– Coercive Field ↓– Retention ↓– Fatigue ↓– Imprint ↓
Extrinsic requirements– Processing temperature ↓– CMOS compatibility ↑– Availability ↑– Cost ↓– ETC…..
Ferroelectric Materials
Basic Phenomena in ferroelectrics – Switching
Switching → nucleation-driven
D.J. Jung et al. Integrated Ferroelectrics 48 (2002) 59
Switching models
Ishibashi-Orihara based on Kolmogov-Avrami*
*Orihara et al, J. Phys. Soc. Jpn. 63 (1994) 1031
- Inhomogeneous nucleation with fixed rate; it occurs at fixed nucleation sites (usually at the interfaces)
kD
C fE =
Ec – coecive fieldf – frequencyD – dimensionality factork – waveform factor
Switching models
nucleation-limited-switching Tagantsev model*
*Tagantsev et al., Phys Rev. B 66 (2002) 214109
i. The film is presented as an ensemble of elementary region.ii. The switching of an elementary region occurs once a domain of reversed
polarization is nucleated in the region.iii. Time needed for switching of an elementary region is equal to the waiting time for
the first nucleation, i.e., the time needed for filling the region with the expanding domain is neglected compared to the waiting time.
iv. The distribution of the waiting times for the ensemble of the elementary regions is smooth and exponentially broad, i.e., covering many decades.
Switching models
Du-Chen model*
*X. Du and I. W. Chen, MRS Proc. 493 (1998) 311D.J. Jung et al., Integrated Feroelectrics 48 (2002) 59
-nucleation process is connected to defects (pinning) -nucleation is thermally activated
2011lnln
CEG
kTff ∆−=
Ec – coecive fieldf – frequency∆G – critical energy
to form a nuclei
⎟⎟⎠
⎞⎜⎜⎝
⎛∆= 20
11expCE
GkT
ττ
Ferroelectric Materials
Fatigue and imprint
Both are defect-driven effects:Switching is hindered by internal fields generated by defects
= domain pinning
virgin
> 106 Cycles
Imprint
virgin
Unipolar Cycles
Ferroelectric Materials
Simple perovskites – ABO3
– Pb(Zr,Ti)O3 – PZT – BaTiO3
Layered perovskites
– SrBi2Ta2O9 – SBT – Bi4Ti3O12 – BiT
A
B
O
TiO6
O
Ti
Bi
TaO6
O
Ta
Bi
Sr
Multiferroics
Multiferroics
Elastic Magnetic
Electric
Ferro ≡ two or more states exists and can be shifted by field
ParaFerroAntiferro
Magneto-elastic
Ferro-elastic Magneto-electric
Multiferroics
Lines and Glass, Principles and applications of ferroelectrics…, Clarendon Press, Oxford, 1977
Multiferroics
Lines and Glass, Principles and applications of ferroelectrics…, Clarendon Press, Oxford, 1977
2. Coupled elastic and magnetic properties – Magnetoelastic:
K2NiF4 : PPP → PFcAc
3. Coupled electric and magnetic properties – Magnetoelectric:
1. Coupled elastic and electric properties – Ferroelastic:
BaTiO3: PPP→FcFcP →FcFcP →FcFcP
RbFeF4 : PPP → PFP → PFA
BaCoF4 : PPP → FPP → FFA
Examples
Multiferroics
*Wang et al., Epitaxial BiFeO3 multiferroic thin film heterostructures, Science (2003) 1719** Erenstein et al Comment on “Epitaxial BiFeO3 Multiferroic Thin Film Heterostructures”, Nature
Example 1 – Ferroelectric and Ferromagnetic*: BiFeO3 – thin epitaxial films
dE/dHMagnetoelectric coefficient
Multiferroics
*Zheng et al., Multiferroic BaTiO3-CoFe2O4 Nanostructures, Science (2004) 661
Extrinsic Magnetoelectric materials*: BaTiO3-CoFe2O4 Nanostructures BaTiO3 Matrix
Multiferroics
*Hur et al., Electric polarization reversal in a multiferroic material induced by magnetic field, Nature, 392 (2004)
Example 2: Intrinsic magneto-electric* TbMn2O5
Switching of polarizationvia magnetic field
II. Nanoscale ferroelectrics
Fabrication of nanosize ferroelectrics
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
??
Lithography
Maskless patterning methods
Ion-beam milling
Fabrication of nanosize ferroelectrics
(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
Ferroelectric characterizationSize effects Size effects -- ion milled PZT structuresion milled PZT structures
Nagarajan et al., Nature Materials 2, pp43, 2003
E-beam lithography
Fabrication: e-beam direct writing
1. Metalorganic layer 1. Metalorganic layer depositiondeposition
2. E2. E--beam exposurebeam exposure
4. Crystallization4. Crystallization3. Developing 3. Developing
Fabrication: e-beam direct writing
Patterned test structure
Fabrication: e-beam direct writing
Annealed 650°CAnnealed 650°C
NonNon--annealedannealed
Fabrication: e-beam direct writing
“Large area” uniform patterning
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
etCell size (nm)
ββ δδ
β=(34±3.7) nmδ=(7.5±4.5) nm
12121
12121
2
2
+⎟⎠⎞
⎜⎝⎛ −⎟
⎠⎞
⎜⎝⎛ −
−⎟⎠⎞
⎜⎝⎛ −⎟
⎠⎞
⎜⎝⎛ −
=Ω
hd
hdδβ
δβ
Imprint lithography
Fabrication methodsFerroelectric nanostructures by imprint lithography
Harnagea et al. APL, Sept. 1 2003
PZT structures on PZT structures on SrTiOSrTiO33:Nb:Nb
Array of 300 nm PZT structuresArray of 300 nm PZT structures6 x 6 µm6 x 6 µm
Imprint lithography
Soft lithography
Soft lithographyMicro Contact Printing Micro Molding
George Whitesides at Harvard
Nanosize ferroelectrics fabricated by self-assembly methods
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
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
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
In
tens
ity (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
Annealing temperature
Nanosize ferroelectrics by self-patterning
800oC 950oC 1100oC
1- D ferroelectric systems
Nanowires
Ferroelectric nanowires
H. Park, Harvard UniversityNanoletters 2, 447 (2002)
Ferroelectric nanowires
H. Park, Harvard UniversityH. Park, Harvard UniversityNanolettersNanoletters 2, 447 (2002)2, 447 (2002)
Nano-shell tubes
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
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)
Ferroelectric nano-tubes
Ferroelectric nano-tubes
100 1000 100000.1
1
10
0.1
1
10
Si absorbtion
Wav
elen
gth
(µm
)
lattice constant (nm)
Si Al2O3
Ferroelectric nano-tubes4’’ wafer4’’ wafer
Summary
Mark Twain
"It is easier to stay out than get out.“