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Q UANTITATIVE TEXTURE Q UANTITATIVE TEXTURE OF OF FERROELECTRIC MODIFIED LEAD ED LEAD FERROELECTRIC MODIFI TITANATE THIN FILMS TITANATE THIN FILMS J. Ricote, D. Chateigner, L. Pardo , M. Alguer , J. Mendiola , M.L. Calzada

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SLIDE 1

Q QUANTITATIVE TEXTURE

UANTITATIVE TEXTURE OF OF FERROELECTRIC MODIFI FERROELECTRIC MODIFIED LEAD ED LEAD TITANATE THIN FILMS TITANATE THIN FILMS

  • J. Ricote, D. Chateigner, L. Pardo†, M. Algueró‡,
  • J. Mendiola†, M.L. Calzada†

Laboratoire de Physique de l'Etat Condensé. Université du Maine-Le Mans (FRANCE)

†Instituto de Ciencia de Materiales de Madrid. CSIC. (SPAIN) ‡ Queen Mary and Westfield College, Univ. of London (UK)

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SLIDE 2

WHY WHY

TEXTURE

TEXTURE

STUDIES

STUDIES

IN

IN

FERROELECTRIC

FERROELECTRIC

THIN

THIN FILMS FILMS

?

? FERROELECTRICS: ❖ Polar materials ❖ Characterised by a spontaneous electric polarisation ❖ The polarisation can be inverted by the application of an electric field ðHYSTERESIS LOOPS. POLAR AXIS for tetragonal compositions is [001] In polycrystalline materials a POLING PROCESS (application of a strong electric field) is required to obtain spontaneous polarisation.

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SLIDE 3

Polycrystalline thin films showing a preferred orientation with the polar axis perpendicular to the film:

ÄDO NOT REQUIRE THE POLING PROCESS Ä HAVE AN IMPROVED FERROELECTRIC BEHAVIOUR

F F A THOROUGH TEXTURE CHARACTERISATION IS NEEDED:

FOR THE CONTROL AND OPTIMISATION OF THE PREPARATION PROCESS OF HIGHLY ORIENTED FERROELECTRIC THIN FILMS REQUIRED FOR APPLICATIONS.

F F UNTIL RECENTLY

QTA HAVE NOT BEEN CARRIED OUT IN THIN FILMS OF FERROELECTRICS

Chateigner et al., Int. Ferro. 19, 1998, 121 Bornand et al., Int. Ferro. 19, 1998, 1

CORRELATION WITH PHYSICAL PROPERTIES NEITHER

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SLIDE 4

MODIFIED MODIFIED

LEAD

LEAD

TITANATE

TITANATE

THIN

THIN

FILMS

FILMS

  • interesting piezo and pyroelectric properties
  • suitable for infrared sensors and electromechanical applications.

FILMS WERE OBTAINED BY SOL-GEL PROCESSING AND DEPOSITION BY SPIN-COATING

PTL ð Pb0.92La0.08TiO3 (20% PbO excess) PTC ð Pb0.76Ca0.24TiO3 (10% PbO excess) SAMPLE SUBSTRATE NUMBER

LAYERS

ANNEALING CONDITIONS

  • HEAT. RATE TEMP--TIME

PTL-4c Pt/TiO2/Si (100) 4 10ºC/min 650°C--12 min PTL-1 to 5 Pt/TiO2/Si (100) 1-5 >500°C/min 650°C--12 min PTC-Si Pt/TiO2/Si (100) 1 30ºC/s 650°C--50 s PTC-Mg Pt/MgO (100) 2 30ºC/s 700°C--50 s PTC-Sr Pt/SrTiO3 (100) 2 30ºC/s 700°C--50 s

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SLIDE 5

QUANTITATIVE QUANTITATIVE

TEXTURE

TEXTURE

ANALYSIS

ANALYSIS

❖ Experimental X-ray POLE FIGURES:

  • asymmetric reflection mode (Cu Kα radiation)
  • 4-circle goniometer with Euler cradle + PSD CPS-120
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SLIDE 6

❖ Scans: 5° x 5° grid, at incidence ω = 11°: sum diagrams ❖ Corrections for asymmetry, volume/absorption Heizmann et al., J. Appl. Cryst. 19 (1986) 467

20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 1000 2000 3000 4000 5000 6000 222 + 222-Pt 113/311 + 311-Pt 103/301 + 311-Si 202/220 +220-Pt + 400-Si 112/211 + 311-Si 102/201/210 002/200 +200-Pt + 220 Si

TiO2

111 + 111-Pt 101/110 001/100

PTC-452 ω = 110 Intensity 2θ (0)

20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 1000 2000 3000 4000 5000 6000

222 + 222-Pt 311 + 311-Pt 310 + 331-Si 221/103/300 400-Si + 220-Pt 112/211 + 311-Si 102/201/210 002/200 +200-Pt + 220-Si 111 + 111-Pt 101/110 TiO2 001/100

PTL-3

Intensity (a.u.) 2θ (°)

PTC PTL

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SLIDE 7

❖ Cyclic integration of {100/001}, {101/110}, {102/201/210}, {112/211} and {221/103/300} overlaps ❖ Corrections for location Bunge et al., Text. Micr. 5 (1982) 153 ❖ ORIENTATION DISTRIBUTION (OD) refinement

  • WIMV algorithm (BEARTEX)
  • crystal symmetry: tetragonal, PTL: 3.93 Å x 4Å

sample triclinic PTC: 3.89 Å x 4.04 Å

  • pole figure ranges:

100/001: 0-70 101/110: 5-70 102/201/210: 15-70 112/211: 35-70 (substrate) 221/103/300: 25-70

  • Overlaps: as for the powder
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SLIDE 8

OD OD-

  • RELIABILITY

RELIABILITY

Separation of tetragonal peaks appeared better than a cubic perovskite-like refinement

Hopefully !! ⇓ {100} vs {001} separation ⇓ polarisation 23 1 mrd 0.3

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SLIDE 9

PTL PTLS

S INVERSE

INVERSE

POLE

POLE

FIGURE

FIGURE

(

(NORMAL TO THE FILM

NORMAL TO THE FILM)

)

PTL-4c PTL-1 PTL-2 PTL-3 PTL-4 PTL-5

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SLIDE 10

PTL PTLS

S INVERSE

INVERSE

POLE

POLE

FIGURE

FIGURE

(

(NORMAL TO THE FILM

NORMAL TO THE FILM)

)

PTC-Sr PTC-Mg PTC-Si 49.16 1 mrd

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SLIDE 11

RESULTS FOR PTL THIN RESULTS FOR PTL THIN FILMS FILMS

Sample Thickness (nm) Components

  • f texture

Texture index (m.r.d.2) RP0 (%) RP1 (%) Remanent polarisation (µC cm-2) PTL-4c 485

weak <110>,<101>

1.3 14 10 13.8 PTL-1 130 <001>,<100>

weak <221>

10.5 36 16

  • PTL-2

210 <001>,<100>

weak <221>

7.5 24 19 7.4 PTL-3 420 <001>,<100>

weak <221>

6.2 22 16 27 PTL-4 500 <001>,<100>

weak <221>

4.6 18 12 19 PTL-5 560 <001>,<100>

weak <221>

3.9 19 15 10.7

High heating rates results in stronger textures. F2 ➘ with thickness .

ð low heat. rate ð affected by leakage

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SLIDE 12

RESULTS FOR PTC THIN RESULTS FOR PTC THIN FILMS FILMS

Sample Components

  • f texture

Texture index (m.r.d.2) RP0 (%) RP1 (%) Pyroelectric coef. γS

spontaneous

γP

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

PTC-Si

Pt/TiO2/Si

weak<001>,<100>

<110>,<101>

2.4 23 12 0.28 2.5 PTC-Mg

Pt/MgO

<001>,<100>

weak <111>

5.2 22 10 1.5 3.2 PTC-Sr

Pt/SrTiO3

<001>,<100> 32.1 26 24 1.1 2.0

Less textured films are easier to pole Substrate: determinant factor of the final texture.

ò

components contribution Poled values are not retained with time

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SLIDE 13

RECALCULATED POLE FI RECALCULATED POLE FIGURES OF PTL THIN GURES OF PTL THIN FILMS FILMS

1 m.r.d. 25.72

PTL-1 PTL-3 PTL-5

Similar contribution

  • f texture

components Thickness é Texture index ê Polar axis contribution ê (<001>) Spontaneous polarisation ê

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SLIDE 14

RECALCULATED POLE FI RECALCULATED POLE FIGURES OF PTC THIN GURES OF PTC THIN FILMS FILMS

PTC-Sr PTC-Mg

50.77 1 m.r.d.

Strong contribution

  • f <100>

component <100> contribution é (⊥ polar axis and non –contributing to polarisation) Spontaneous polarisation ê Spontaneous pyroelectricity ê

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SLIDE 15

THICKNESS THICKNESS

EFFECTS

EFFECTS

ON

ON

TEXTURE

TEXTURE

AND

AND PROPERTIES PROPERTIES

THE USE OF A HIGH HEATING RATE ENHANCES THE APPEARANCE OF

PREFERENTIAL ORIENTATION. During slow heating several variants of texture

can be nucleated, resulting in a random thin film. AS THE NUMBER OF LAYERS INCREASES THE TEXTURE INDEX DECREASES. THIS

SEEMS TO INDICATE HETEROGENEOUS NUCLEATION, I.E., WHEN CRYSTALS NUCLEATE IN SITES THROUGHOUT THE THICKNESS OF THE FILM.

Except for the very thin PTL-1 and PTL-2 films, which present high leakage currents, the remanent polarisation decreases as the texture strength of the film

  • decreases. An increase of the texture index involves in this case a higher

fraction of crystals oriented with the polar axis, <001>, perpendicular to the film surface. The largest contribution to the net polarisation comes from these

  • crystals. Therefore, there is an increase of the polarisation of the film.
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SLIDE 16

THE INCREASE OF THE FILM THICKNESS BY INCREASING THE NUMBER OF

DEPOSITED LAYERS LEADS TO A DECREASE OF THE TEXTURE STRENGTH THAT RESULTS IN A REDUCTION OF THE REMANENT POLARISATION.

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SLIDE 17

SUBSTRATE EFFECTS ON SUBSTRATE EFFECTS ON TEXTURE AND TEXTURE AND PROPERTIES PROPERTIES

  • DIFFERENT SUBSTRATES LEAD TO:

DIFFERENT OVERALL DEGREE OF ORIENTATION DIFFERENT CONTRIBUTIONS FROM <100> AND <001> COMPONENTS

USE OF THE TRADITIONAL PT/TIO2/SI SUBSTRATE RESULTS IN:

WEAKLY TEXTURED FILMS LOW SPONTANEOUS PYROELECTRIC COEFFICIENTS

  • PTC-Sr: largest <100>⊥ component: lowest PYROELECTRIC COEFFICIENTS

THE USE OF A PT/SRTIO3 SUBSTRATE, COMPARED TO PT/MGO, PRODUCES

HIGHLY TEXTURED FILMS, BUT WITH A STRONG CONTRIBUTION FROM CRYSTALS WHOSE POLAR AXIS IS IN THE PLANE OF THE FILM, WHICH REDUCES THE SPONTANEOUS PYROELECTRIC COEFFICIENTS OF THE FILMS.

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SLIDE 18

SUMMARY SUMMARY

A QUANTITATIVE TEXTURE ANALYSIS HAS BEEN CARRIED OUT FOR THE FIRST TIME ON

SEVERAL FERROELECTRIC THIN FILMS OF MODIFIED LEAD TITANATE.

The effects of different processing parameters on the final texture have been studied: F rapid thermal annealing gives highly texture films F heterogeneous nucleation of the perovskite: for higher thicknesses, lower texture strengths F choice of substrate: determinant factor for texture, then properties Remanent polarisation and pyroelectric coefficients can be correlated to the texture strength and the contribution of the different texture components. A A CKNOWLEDGEMENTS

CKNOWLEDGEMENTS

Grant awarded by the regional government of Pays de Loire and the French Education Ministry Work financed by projects MAT98-1068 (Spanish CICYT) and COPERNICUS CIPA-CT94-0236 Declared of technological interest by the EU COST514 action on ferroelectric thin films.

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SLIDE 19

REFERENCES

  • J. Ricote & D. Chateigner: Aplicación del Análisis Cuantitativo de la Textura al Estudio de Láminas

Delgadas Ferroeléctricas. To appear Boletín de la Sociedad Española de Cerámica y Vidrio

  • J. Ricote, D. Chateigner, L. Pardo, M. Alguero, J. Mendiola & M.L. Calzada: Quantitative analysis of

preferential orientation components of ferroelectric thin films. To appear in Ferroelectrics

  • J. Ricote, D. Chateigner, G. Ripault, L. Pardo, M. Alguero, J. Mendiola & M.L. Calzada: Quantitative

texture of ferroelectric modified lead titanate thin films. In "Textures of Materials, vol. 2" (Ed J.A. Szpunar), NRC Research Press, Ottawa 1999, p1327-1332.

  • D. Chateigner, H.-R. Wenk, A. Patel, M. Todd & D.J. Barber: Analysis of preferential orientations in

PST and PZT layers on various substrates. Integrated Ferroelectrics 19, 1998, 121-140.

  • V. Bornand, D. Chateigner, P. Papet & E. Philippot: Heteroepitaxial growth of LiTaO3 thin films by

pyrosol process. Integrated Ferroelectrics 19, 1998, 1-10.

  • V. Bornand, D. Chateigner, P. Papet & E. Philippot: Piezoelectric thin films prepared by pyrosol
  • process. Annales de Chimie Sci. Mat. 22, 1997, 683-686.