Improvements in the X- -ray characterisation of ray - - PowerPoint PPT Presentation

Improvements in the X Improvements in the X-

• ray characterisation of

ray characterisation of electroceramic electroceramic thin films thin films by the application by the application of a

• f a

novel combined analysis novel combined analysis procedure procedure

J.

• J. Ricote

Ricote ICMM ICMM-

• CSIC. (Spain)
• CSIC. (Spain)

D.

• D. Chateigner

Chateigner CRISMAT CRISMAT-

• ENSICAEN (France)

ENSICAEN (France) L.

• L. Lutterotti

Lutterotti Università Università di Trento di Trento (Italy) (Italy)

• Dr. J.
• Dr. J. Ricote

Ricote

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

OUTLINE OUTLINE

Introduction Introduction Ferroelectric thin films and texture Ferroelectric thin films and texture Combined method of X Combined method of X-

• ray diffraction analysis

ray 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

• f substrate and film.
• f substrate and film.

Conclusions Conclusions

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 material The 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 figure Generation of a pole figure

X X-

• ray

ray χ χ Sample Sample ϕ ϕ ω ω

25.72 1 m.r.d. (111)

ϕ χ

90

m.r.d. = multiple of a random distribution (a sample without any preferred

• rientation shows pole figures with

constant values of 1 m.r.d.)

Pole figure Pole figure

ω = 20°

χ

60° 0°

Refinement of individual spectra Refinement of individual spectra

Ferroelectric Materials Department

Equipment used for pole figure measurements Equipment 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 QUality Improvement-ESQUI”

Ferroelectric Materials Department

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

11.54 1 m.r.d. 0.01

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

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

Ferroelectric Materials Department

Quantitative Texture Analysis Quantitative Texture Analysis [ ]

i i i

g g f F ∆ =

∑

2 2 2

) ( 8 1 π

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 films ferroelectric thin films

Ferroelectric Materials Department

Thickness dependence of texture

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 <001> and <100> orientation)

2 4 6 8 10 12

direct insertion

Texture index (m.r.d.

2)

1 2 3 4 5 2 4 6 8 10 12

number of layers RTP layer-by-layer

Thickness effect disappears with the layer-by-layer crystallization

PTL 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 properties Deduction of effective physical properties

Ferroelectric Materials Department

*PTL: Lanthanum modified lead titanate

GPa x / 10 6 . 9 5 . 14 5 . 14 3 . 33 1 . 7 1 . 7 1 . 7 5 . 6 35 . 1 . 7 35 . 5 . 6

3 −

                    − − − − − −

S =

Geometric mean PTL on Ti/Pt/Ti/(100)Si Mixed <111> and <001>,<100> orientation PTL on Pt/TiO2/(100)Si Mixed <001>,<100> orientation

GPa x / 10 3 . 13 9 . 12 9 . 12 3 . 10 4 . 3 4 . 3 4 . 3 1 . 10 2 . 3 4 . 3 2 . 3 1 . 10

3 −

                    − − − − − − GPa x / 10 2 . 13 2 . 13 3 . 13 9 . 9 2 . 3 2 . 3 2 . 3 9 . 9 2 . 3 2 . 3 2 . 3 9 . 9

3 −

                    − − − − − − Elastic properties of tetragonal PbTiO3 single crystal

Kalinichev et al. J. Mater.

• Res. 12, 2623 (1997)

Sc =

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

Further advances in X Further advances in X-

• ray characterisation:

ray characterisation: Combined analysis Combined analysis

RESIDUAL STRESS Stress distribution function

Stress analysis Rietveld refinement

LATTICE PARAMETERS

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 METHOD OF 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 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

Intensity (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 = ? Å c = ? Å Lattice parameters are affected by STRESS in thin films Ca modified lead titanates (PCT): a = 3.8939 Å c = 4.0496 Å

(bulk ceramic values JCPDS 39-1336)

20 25 30 35 40 45 50 55 60 5 10 15 20 25 30

112 211 102 201 210 002, 200 200-Pt 111 111-Pt 100 101,110 001

Intensity (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:

• verlapping
• f

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 contributions Separation of the contribution of texture contributions

(simple Quantitative Texture Analysis)

20 22 24 26 20 40 60 80 100 120

χ = 20º χ = 15º χ = 5º χ = 0º χ =10º

Intensity (a.u.) 2θ (º)

20 22 24 26 20 40 60 80 100

χ = 10º χ = 15º χ = 5º χ = 0º

Intensity (a.u.) 2θ (º)

PCT/Pt/MgO PCT/Pt/MgO

<100> orientation <100> orientation <001> orientation <001> orientation

001 100 (simple Quantitative Texture Analysis)

χ = 20º

001 100

PCT/Pt/TiO2/Si PCT/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. <001> <100>

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

QTA results: Estimated contribution texture components <001> <100>

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

Ferroelectric Materials Department

Separation of the contribution of texture contributions Separation of the contribution of texture contributions

(Combined Method) (Combined Method)

Ferroelectric Materials Department

QTA results: Estimated contrib. <001> <100> c = 3.877 Å c = 3.877 Å a = 3.977 Å a = 3.977 Å

7% 7% 93% 93% PCT/Pt/TiO2/Si PCT/Pt/TiO2/Si PCT/Pt/MgO PCT/Pt/MgO

c = 3.883 Å c = 3.883 Å a = 4.020 Å a = 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 <001> and <100> contributions is possible.

Pyroelectric Coefficient

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

σ = +1182 MPa 0.3 1.5 σ = -700 MPa Simultaneously, we observe the effect

• f the applied stress on the lattice

parameters

Simultaneous Simultaneous texture determination of substrate and film texture determination of substrate and film

(Combined Method) (Combined Method)

0.01 75 1 m.r.d.

Texture index F2 (mrd2) R factors (%)

non-treated substrate

Pt 129 RW=13, RB=12

annealed substrate

Pt 199 RW=8, RB=14 Pt (Recryst. 1h) 199 RW=9, RB=20 Pt (Recryst. 2h) 195 RW=9, RB=14 Pt (Recryst. 3h) 222 RW=27, RB=12

Ferroelectric Materials Department

Pt layer <111> fibre orientation Pt layer <111> fibre orientation

Annealing of the substrate, which involves crystal growth, results in an increase of the degree of

• rientation of the Pt layer.

New information on the Pt layer provided by the combined method

Texture determination of film Texture determination of film

(Combined Method) (Combined Method)

1 m.r.d. 0.01 9.5

Texture index F2 (mrd2)

non-treated substrate

PTC 5.2

annealed substrate

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

PCT film PCT film

Effect on the degree of

• rientation of the PCT film

PCT film on untreated substrate Strong <100> orientation

5.8 1 m.rd. 0.04

PCT film on annealed substrate Strong <111> orientation Effect of the annealing of the substrate in the type of texture developed

Ferroelectric Materials Department

New information on contribution

• f texture components provided

by the combined method

Small <111> texture contribution not observed by conventional QTA

CONCLUSIONS CONCLUSIONS

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,

• btained by the combined method. We have shown two examples:

Separation of <001>,<100> components Reveal of small <111> 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)

Acknowledgements Acknowledgements

European-GROWTH project (G6TD-CT99-00169) “x-ray Expert System for electronic films QUality Improvement-ESQUI” CSIC-CNRS collaboration projects Advanced fellowship Advanced fellowship “Ramón y Cajal” Ramón y Cajal”

Additional funding: Delegation Regionale a la Recherche et a la Technologie de Basse Normandie

COST Action 528 Chemical Solution Deposition of Thin Films