Improvements in the XImprovements in the X--ray characterisation of ray characterisation of

electroceramicelectroceramic thin filmsthin films by the applicationby the application of a of a

novel combined analysisnovel combined analysis procedureprocedureJ. J. RicoteRicote ICMMICMM--CSIC. (Spain)CSIC. (Spain)

D. D. ChateignerChateigner CRISMATCRISMAT--ENSICAEN (France)ENSICAEN (France)

L. L. LutterottiLutterotti UniversitàUniversità di Trentodi Trento (Italy)(Italy)

Dr. J. Dr. J. RicoteRicote

Ferroelectric Materials DepartmentMaterials Science Institute of Madrid Spanish Council of Scientific Research

OUTLINEOUTLINE

Introduction Introduction Ferroelectric thin films and textureFerroelectric thin films and textureCombined method of XCombined method of X--ray diffraction analysisray diffraction analysis

Results of the analysis of ferroelectric thin films with Results of the analysis of ferroelectric thin films with the combined method the combined method

Separation of the contribution of different texture Separation of the contribution of different texture components.components.Simultaneous texture and structure determination Simultaneous texture and structure determination of substrate and film.of substrate and film.

ConclusionsConclusions

Ferroelectric Materials Department

The figures of merit that determine the efficiency of ferroelectric materials in technological applications (i.e. piezoelectric coefficient in MEMS) strongly depends on the net polarization of the materialThe polarization value depends on several factors, among them: TEXTURE. Preferential orientation along the polar axis produces an improved ferroelectric behaviour

Improvement of performance by texture Improvement of performance by texture control in ferroelectric thin films control in ferroelectric thin films

Ferroelectrics are polar dielectrics in which the direction of polarization can be re-oriented by application of an electric field.

Ferroelectrics are polar dielectrics in which the direction of polarization can be re-oriented by application of an electric field.

In general, the polycrystalline ferroelectric materials need a Poling process with an intense electric field, in order to obtain any spontaneous polarization. This is not needed in highly textured thin films along the polar axis

Ferroelectric Materials Department

Generation of a pole figureGeneration of a pole figure

XX--rayray

χχSampleSample

ϕϕ

ωω

25.72

1 m.r.d.

0

(111) ϕ

χ0 90

m.r.d. = multiple of a random distribution

(a sample without any preferred orientation shows pole figures with

constant values of 1 m.r.d.)

Pole figurePole figure

ω = 20°

χ

60°

0°

Refinement of individual spectraRefinement of individual spectra

Ferroelectric Materials Department

Equipment used for pole figure measurementsEquipment used for pole figure measurements

DIFFRACTOMETER EQUIPED WITH:• Four-circle goniometer

• Curve position sensitive detector (PSD)

(MDM-Italy; developed in the ESQUI project)

European-GROWTH project“x-ray Expert System for electronic films QUalityImprovement-ESQUI”

Ferroelectric Materials Department

Advanced texture determination: Advanced texture determination: Quantitative Texture AnalysisQuantitative Texture Analysis

11.54

1 m.r.d.

0.01

From the experimental pole figures we obtain by an iterative process anORIENTATION DISTRIBUTION FUNCTION (ODF)

Recalculated pole figures from ODF

Experimental pole figures (incomplete)f(g); g = α,β,γ

Ferroelectric Materials Department

Quantitative Texture AnalysisQuantitative Texture Analysis

[ ] ii

i ggfF ∆= ∑ 222 )(81π

Orientation Distribution Function (ODF)

Texture Index (F2) Inverse pole figures(degree of orientation) (texture components)

PZTp252b PZTp252c

110

101

011

010

001 100

111

1 m.r.d.

0.01

32.07

Inverse pole figure:It describes the densities for crystal directions falling into the fixed sample direction y.

Contributions of the different components can be estimated

Ferroelectric Materials Department

Quantitative Texture Analysis of polycrystalline Quantitative Texture Analysis of polycrystalline ferroelectric thin filmsferroelectric thin films

Ferroelectric Materials Department

Thickness dependence of texture

0

1 m.r.d.

25.72

PTL-1 PTL-3 PTL-5

110 nm 250 nm 370 nm

Similar contribution of the texture components(mixed and orientation)

0

2

4

6

8

10

12 direct insertion

Text

ure

inde

x (m

.r.d.

2 )

0 1 2 3 4 50

2

4

6

8

10

12

number of layers

RTP layer-by-layer

Thickness effect disappears with the layer-by-layer crystallizationPTL on Pt/TiO2/(100)Si

*PTL: Lanthanum modified lead titanate

J. Ricote et al. J. Am. Ceram. Soc., 86 [9], 1571-77 (2003)

Deduction of effective physical propertiesDeduction of effective physical properties

Ferroelectric Materials Department

*PTL: Lanthanum modified lead titanate

GPax /10

6.90000005.140000005.140000003.331.71.70001.75.635.00001.735.05.6

3−

−−−−−−

S =

Geometric mean

PTL on Ti/Pt/Ti/(100)SiMixed and, orientation

PTL on Pt/TiO2/(100)Si Mixed , orientation

GPax /10

3.130000009.120000009.120000003.104.34.30004.31.102.30004.32.31.10

3−

−−−−−−

GPax /10

2.130000002.130000003.130000009.92.32.30002.39.92.30002.32.39.9

3−

−−−−−−

Elastic properties of tetragonal PbTiO3 single crystalKalinichev et al. J. Mater. Res. 12, 2623 (1997)

Sc =

J. Ricote et al. Mat. Sci. Forum 426-432, 3433-38 (2003)

Further advances in XFurther advances in X--ray characterisation: ray characterisation: Combined analysisCombined analysis

RESIDUAL STRESSStress distribution function

Stress analysis

Rietveld refinement

LATTICEPARAMETERS

Software used is MAUD

General purpose program for diffraction spectra fitting developed by L.Lutterotti. http://www.ing.unitn.it/~luttero/maud/

Generally, labs perform a partial determination of these parameters

It allows a simultaneous and more precise determination of parameters

INTEGRATED INTENSITIES

Iterative process WIMV

Orientation Distribution Function

Ferroelectric Materials Department

RESULTS OF THE APPLICATION RESULTS OF THE APPLICATION OF THE COMBINED METHODOF THE COMBINED METHOD

Limitations of the simple Quantitative Texture Analysis (I)Limitations of the simple Quantitative Texture Analysis (I)

21.0 21.5 22.0 22.5 23.0 23.5 24.0 24.5

0

2

4

6

8

10

12

14

16

18

20

001

100

PCT thin film on MgO based substrate

PCT thin film on Si based substrate

Bulk PCT ceramic

Inte

nsity

(a.u

.)

2θ (º)

Ferroelectric Materials Department

We need to know the lattice parameters prior to the texture analysis

PCT thin films on Pt/TiO2/(100)Si:

a = ? Åc = ? Å

Lattice parameters are affected by STRESS in thin films

Ca modified lead titanates (PCT):

a = 3.8939 Åc = 4.0496 Å

(bulk ceramic values JCPDS 39-1336)

20 25 30 35 40 45 50 55 600

5

10

15

20

25

30

112211

102201210

002, 200200-Pt

111111-Pt

100

101,110

001In

tens

ity (a

.u.)

2θ (º)

PCT thin film

We need a simultaneous analysis of texture and structure of both film and substrate to

solve completely the texture of the films Ferroelectric Materials Department

TEXTURE effects:peaks that do not appear at low χ angles

Pt reflections

Substrate influence:overlapping of reflections from the film and the substrate

Limitations of the simple Quantitative Texture Analysis (II)Limitations of the simple Quantitative Texture Analysis (II)

Structural parameters are difficult to obtain due to:

Separation of the contribution of texture contributionsSeparation of the contribution of texture contributions(simple Quantitative Texture Analysis)

20 22 24 260

20

40

60

80

100

120

χ = 20º

χ = 15º

χ = 5º

χ = 0º

χ =10º

Inte

nsity

(a.u

.)

2θ (º)

20 22 24 260

20

40

60

80

100

χ = 10º

χ = 15º

χ = 5º

χ = 0º

Inte

nsity

(a.u

.)

2θ (º)

PCT/Pt/MgOPCT/Pt/MgO orientation orientation

orientation orientation

001 100

(simple Quantitative Texture Analysis)

χ = 20º001 100PCT/Pt/TiO2/SiPCT/Pt/TiO2/Si PCT film under tensile stress:

σ = +1182 Mpa

PCT film under compressive stress:σ = -700 Mpa

QTA results:Estimated contribution

texture components.

62%!!62%!! 38%!!38%!!

QTA results:Estimated contribution

texture components

55%!!55%!! 45%!!45%!!

Ferroelectric Materials Department

Separation of the contribution of texture contributionsSeparation of the contribution of texture contributions(Combined Method)(Combined Method)

Ferroelectric Materials Department

QTA results:

Estimated contrib.

c = 3.877 Åc = 3.877 Åa = 3.977 Åa = 3.977 Å 7%7% 93%93%

PCT/Pt/TiO2/SiPCT/Pt/TiO2/Si

PCT/Pt/MgOPCT/Pt/MgOc = 3.883 Åc = 3.883 Åa = 4.020 Åa = 4.020 Å 68%68% 32%32%

Instead of the integration of the overlapped peak (“integral approach”), and separating both contributions during the WIMV process, the combined method allows to deconvolute the peaks first, before the ODF calculation starts. As a result a more correct estimation of the contributions of and contributions is possible.

PyroelectricCoefficient(10-8 C cm-2 K-1)

σ = +1182 MPa0.3

1.5σ = -700 MPa

Simultaneously, we observe the effect of the applied stress on the lattice parameters

SimultaneousSimultaneous texture determination of substrate and filmtexture determination of substrate and film(Combined Method)(Combined Method)

0.01

75

1 m.r.d.

Texture indexF2 (mrd2) R factors (%)

non-treated substratePt 129 RW=13, RB=12annealed substratePt 199 RW=8, RB=14Pt (Recryst. 1h) 199 RW=9, RB=20Pt (Recryst. 2h) 195 RW=9, RB=14Pt (Recryst. 3h) 222 RW=27, RB=12

Ferroelectric Materials Department

Pt layer fibre orientation

Pt layer fibre orientation

Annealing of the substrate, which involves crystal growth, results in an increase of the degree of orientation of the Pt layer.

New information on the Pt layer provided by the combined method

Texture determination of filmTexture determination of film(Combined Method)(Combined Method)

1 m.r.d.

0.01

9.5

Texture indexF2 (mrd2)

non-treated substratePTC 5.2

annealed substratePTC 2.1 PTC (Recryst. 1h) 2.1 PTC (Recryst. 2h) 2.5 PTC (Recryst. 3h) 2.5

PCT filmPCT film

Effect on the degree of orientation of the PCT film

PCT film on untreated substrateStrong orientation

5.8

1 m.rd.

0.04

PCT film on annealed substrateStrong orientation

Effect of the annealing of the substrate in the type of texture developed Ferroelectric Materials Department

New information on contribution of texture components provided by the combined method

Small texture contribution not observed by conventional QTA

CONCLUSIONSCONCLUSIONS

The application of the combined method to ferroelectric calcium modified lead titanate thin films has proved to produce more accurate and reliable results than more traditional X-ray diffraction analysis approaches. It also provides simultaneously information on the structure, microstructure and texture of both the deposited film and the substrate, revealing important characteristics of the Pt layer used in this study as bottom electrode.

An important aspect covered is the better resolution of the texture and, specifically of the contribution of the different texture components, obtained by the combined method. We have shown two examples:

Separation of , componentsReveal of small texture component

Ferroelectric Materials Department

see also:J. Ricote and D. Chateigner J. Appl. Cryst. 37, 91-95 (2004) J. Ricote et al. Thin Solid Films 450, 128-133 (2004)

AcknowledgementsAcknowledgements

European-GROWTH project (G6TD-CT99-00169)“x-ray Expert System for electronic films QUality Improvement-ESQUI”

CSIC-CNRS collaboration projects

Advanced fellowship “Ramón y Cajal”

Additional funding:

Delegation Regionale a la Recherche et a la Technologie de Basse Normandie

COST Action 528Chemical Solution Deposition of Thin Films