Improvements in the X- -ray characterisation of ray characterisation of Improvements in the X electroceramic thin films thin films by the application by the application of a of a electroceramic novel combined analysis procedure procedure novel combined analysis J. Ricote Ricote ICMM ICMM- -CSIC. (Spain) CSIC. (Spain) J. D. Chateigner Chateigner CRISMAT CRISMAT- -ENSICAEN (France) ENSICAEN (France) D. L. Lutterotti Lutterotti Università Università di Trento di Trento (Italy) (Italy) L. Dr. J. Ricote Ricote Dr. J. 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- -ray diffraction analysis ray diffraction analysis Combined method of X 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. Conclusions Conclusions Ferroelectric Materials Department
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 Ferroelectrics are polar dielectrics in which the direction of polarization can be re-oriented by application of an electric polarization can be re-oriented by application of an electric field. field. � 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 � 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- -ray ray X ϕ ϕ Pole figure Pole figure ω ω ϕ (111) χ χ 25.72 Sample Sample 1 m.r.d. 0 χ 90 ω = 20° 60 ° 0 χ m.r.d. = multiple of a random distribution (a sample without any preferred 0° orientation shows pole figures with Refinement of individual spectra constant values of 1 m.r.d.) 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 From the experimental pole figures we obtain by an iterative process an ORIENTATION DISTRIBUTION FUNCTION (ODF) Experimental pole figures (incomplete) f(g); g = α , β , γ 11.54 1 m.r.d. 0.01 Recalculated pole figures from ODF Ferroelectric Materials Department
Quantitative Texture Analysis Quantitative Texture Analysis Orientation Distribution Function (ODF) � � Texture Index (F 2 ) Inverse pole figures (degree of orientation) (texture components) 1 [ ] ∑ 2 = ∆ F f ( g ) g 2 i i π 8 2 PZTp252b PZTp252c i 32.07 1 m.r.d. 010 0.01 110 Inverse pole figure: 011 111 It describes the densities for Contributions of the different crystal directions falling into components can be estimated 001 101 100 the fixed sample direction y. Ferroelectric Materials Department
Quantitative Texture Analysis of polycrystalline Quantitative Texture Analysis of polycrystalline ferroelectric thin films ferroelectric thin films Thickness dependence of texture 12 direct insertion 10 110 nm 250 nm 370 nm 8 6 25.72 2 ) Texture index (m.r.d. 4 2 1 m.r.d. 0 12 RTP layer-by-layer 10 0 8 6 Similar contribution of the texture components PTL-1 PTL-3 PTL-5 (mixed <001> and <100> orientation) 4 2 Thickness effect disappears with the layer-by-layer crystallization PTL on Pt/TiO 2 /(100)Si 0 0 1 2 3 4 5 number of layers *PTL: Lanthanum modified lead titanate J. Ricote et al. J. Am. Ceram. Soc., 86 [9], 1571-77 (2003) Ferroelectric Materials Department
Deduction of effective physical properties Deduction of effective physical properties − − 6 . 5 0 . 35 7 . 1 0 0 0 Elastic properties of − − 0 . 35 6 . 5 7 . 1 0 0 0 tetragonal − − S c = 7 . 1 7 . 1 33 . 3 0 0 0 PbTiO 3 single crystal − x 10 3 / GPa 0 0 0 14 . 5 0 0 Kalinichev et al. J. Mater. Res. 12, 2623 (1997) 0 0 0 0 14 . 5 0 0 0 0 0 0 9 . 6 Geometric mean − − 10 . 1 3 . 2 3 . 4 0 0 0 − − 9 . 9 3 . 2 3 . 2 0 0 0 − − 3 . 2 10 . 1 3 . 4 0 0 0 − − 3 . 2 9 . 9 3 . 2 0 0 0 − − 3 . 4 3 . 4 10 . 3 0 0 0 S = − − 3 . 2 3 . 2 9 . 9 0 0 0 − x 10 3 / GPa − x 10 3 / GPa 0 0 0 12 . 9 0 0 0 0 0 13 . 3 0 0 0 0 0 0 12 . 9 0 0 0 0 0 13 . 2 0 0 0 0 0 0 13 . 3 0 0 0 0 0 13 . 2 PTL on Pt/TiO 2 /(100)Si PTL on Ti/Pt/Ti/(100)Si Mixed <111> and Mixed <001>,<100> orientation <001>,<100> orientation *PTL: Lanthanum modified lead titanate J. Ricote et al. Mat. Sci. Forum 426-432, 3433-38 (2003) Ferroelectric Materials Department
Further advances in X- -ray characterisation: ray characterisation: Further advances in X Combined analysis Combined analysis INTEGRATED INTENSITIES Generally, labs perform a partial determination of these parameters Iterative process WIMV Orientation Distribution Function It allows a simultaneous and more precise determination of Rietveld parameters refinement LATTICE PARAMETERS Software used is MAUD General purpose program for diffraction Stress spectra fitting developed by L.Lutterotti. analysis http://www.ing.unitn.it/~luttero/maud/ RESIDUAL STRESS Stress 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) We need to know the lattice parameters prior to the texture analysis 20 Ca modified lead 100 18 PCT thin film on titanates (PCT): 16 Si based substrate 001 14 a = 3.8939 Å 12 c = 4.0496 Å Intensity (a.u.) PCT thin film on 10 (bulk ceramic values MgO based substrate 8 JCPDS 39-1336) 6 Lattice parameters 4 are affected by 2 Bulk PCT ceramic STRESS in thin films 0 21.0 21.5 22.0 22.5 23.0 23.5 24.0 24.5 PCT thin films on 2 θ (º) Pt/TiO 2 /(100)Si: a = ? Å c = ? Å Ferroelectric Materials Department
Limitations of the simple Quantitative Texture Analysis (II) Limitations of the simple Quantitative Texture Analysis (II) Structural parameters are difficult to obtain due to: Substrate influence: 30 overlapping of 111 111-Pt PCT thin film reflections from the film 25 and the substrate 20 Intensity (a.u.) Pt reflections 001 15 TEXTURE effects: peaks that do not appear 100 10 at low χ angles 002, 200 102 200-Pt 5 101,110 112 201 211 210 0 20 25 30 35 40 45 50 55 60 2 θ (º) We need a simultaneous analysis of texture and structure of both film and substrate to Ferroelectric Materials Department solve completely the texture of the films
Separation of the contribution of texture contributions Separation of the contribution of texture contributions (simple Quantitative Texture Analysis) (simple Quantitative Texture Analysis) PCT/Pt/TiO 2 /Si PCT/Pt/TiO 2 /Si 001 100 PCT film under tensile stress : χ = 20º σ = +1182 Mpa 100 χ = 15º 80 QTA results: Intensity (a.u.) 60 χ = 10º Estimated contribution texture components. 40 χ = 5º <001> <100> 20 62%!! 38%!! 62%!! 38%!! χ = 0º 0 20 22 24 26 2 θ (º) <100> orientation <100> orientation PCT film under compressive stress: PCT/Pt/MgO PCT/Pt/MgO 001 100 120 σ = -700 Mpa χ = 20º 100 χ = 15º QTA results: 80 Intensity (a.u.) Estimated contribution 60 χ =10º texture components 40 <001> <100> χ = 5º 55%!! 45%!! 55%!! 45%!! 20 χ = 0º 0 20 22 24 26 Ferroelectric Materials Department 2 θ (º) <001> orientation <001> orientation
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