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Developments in Dielectric Materials and

Electronic Devices

Ceramic Transactions Volume 167

Proceedings of the 106th Annual Meeting of The American Ceramic Society, Indianapolis, Indiana, USA (2004)

Editors K. M. Nair

R. Guo A.S. Bhalla S-l. Hirano D. Suvorov

Published by

The American Ceramic Society PO Box 6136

Westerville, Ohio 43086-6136 www.ceramics.org

Developments in Dielectric Materials and Electronic Devices

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ISBN 1-57498-188-9

iv · Developments in Dielectric Materials and Electronic Devices

Contents Preface ix

Material Design, Synthesis & Properties Hydrothermal Synthesis and Properties of Sodium-Doped Bismuth Titanate Powders 3

E.B. Slamovich, H. Xu, S. Mallick, W.F. Shelley, H.Y. Li, and K.J. Bowman

Novel Processing of Functional Ceramic Films by CSD with UV Irradiation 13

K. Kikuta, K. Noda, R. Kono, T. Yamaguchi, K. Morita, K. Takagi, and S. Hirano

Processing and Dielectric Properties of La(Zn1/2Ti1/2)03 and Nd(Zn1/2Ti1/2)03 21

R. Ubic, K. Khamoushi, D. Iddles, and T. Price

Effect of Synthesis Parameters on Nanocrystalline PZT Powder 31 A. Banerjee and S. Bose

Nanocrystalline Lead Free Piezoceramic (KxNa«|.x)Nb03 Derived From Microemulsion Mediated Synthesis 41

C. Pithan, Y. Shiratori, A. Magrez, J. Dornseiffer, and F.-H. Haegel

Variable-Temperature Microwave Dielectric Properties of Single-Crystal Fluorides 51

R.G Geyer, J. Baker-Jarvis, and J. Krupka

Temperature and Frequency Dependence of Dielectric Properties in BST 57

D. Potrepka, S. Tidrow, A. Tauber, F. Crowne, and B. Rod

The Optical and Electrical Properties of Nanocrystalline La0 4Sr0 6Ti03

Thin Films 67 T. Suzuki, P. Jasinski, V. Petrovsky, and H.U. Anderson

Relationship Between Microstructure and Electrical Properties in Various Rare-Earth Doped BME Materials 77

S. Sato, Y. Fujikawa, and T. Nomura

Effects of Lead Stoichiometry on the Microstructure and Mechanical Properties of PZT 95/5 89

C.S. Watson and P. Yang

Microstructure Evolution and Ferroelectric Domains in Nb205 and CaZr03 Doped BaTi03 99

V.V. Mitic, Lj.M. Zivkovic, V.V. Paunovic, Lj.M. Vracar, and M.M. Miljkovic

Developments in Dielectric Materials and Electronic Devices · v

Microstructure and Microwave Dielectric Properties of (1-x)ZnNb206-xZnTa206 Ceramics 109

L. Li, Y. Zhang, Z. Yue, and Z. Gui

The Synergistic Effects of Nb/Mn and Sb/Mn on the Microstructure and Electrical Characteristics of BaTi03 Based Ceramics 117

Lj.M. Zivkovic, V.V. Mitic, V.V. Paunovic, Lj.M. Vracar, B.D. Stojanovic, K. Peron, and MA. Zagete

Thermoelectric Properties of Ca-Doped (ZnO)mln203 Ceramics and Their Improvement Upon Texture 127

H. Kaga, R. Asahi, and T. Tani

Materials for Electronic Devices BaTi03: From Nanopowders to Dense Nanocrystalline Ceramics 139

M.T. Buscaglia, V. Buscaglia, M. Viviani, L. Mitoseriu, P. Nanni, and A. Testino

Crystallization, Microstructure and Dielectric Properties of PbO-BaO-SrO-Nb205-B203-Si02 Based Glass-Ceramics 151

C.-T. Cheng, M. Lanagan, B. Jones, and M.-J. Pan

Polarization Properties and Ferroelectric Distortion of La-Substituted Bi4Ti3012 Ceramics: Comparisons with V- and Nb-Doped Ceramics 167

Y. Noguchi, M. Soga, M. Takahashi, and M. Miyayama

Dielectric Ceramics from the Ti02-Te02 and Bi203-Te02 Systems 175 M. Udovic, M. Valant, and D. Suvorov

Origin of High Dielectric Properties of NM-Sized Barium Titanate Crystallites 189

S. Wada, T. Hoshina, H. Yasuno, S.-M. Nam, H. Kakemoto, T. Tsurumi, and M. Yashima

Piezoelectric Properties of Bismuth Sodium Titanate Ceramics 213 H. Nagata, T. Shinya, Y. Hiruma, T. Takenaka, I. Sakaguchi, and H. Haneda

Nonlead Perovskite Piezoelectric Materials 223 S. Priya, K. Uchino, and A. Ando

MEMS Device Arrays Using Thick Composite PZT Films 235 Z. Wang, W. Zhu, C. Zhao, C. Chao, H. Zhu, J. Miao, Y Wang, and W.S. Gan

Thick Piezoelectric Films from Laser Transfer Process 245 B. Xu, D. White, J. Zesch, A. Rodkin, S. Buhler, J. Fitch, and K. Littau

Multilayer Devices Comprised of Piezoceramic Thin Films on Dielectric Substrates 259

A. Ballato

Dielectric Properties and Tunability of (Ba-j.xSrJTiOsiMgO Composites 271 S. Agrawal, R. Guo, D. K. Agrawal, and A. S. Bhalla

vi · Developments in Dielectric Materials and Electronic Devices

Dynamic Linear Electrooptic Property Influnced by Piezoelectric Resonance in PMN-PT Crystals 277

S. Johnson, K. Reichard, and R. Guo

Electronic Devices & Applications Type I Base-Metal Electrode Multilayer Ceramic Capacitors 291

J. Bernard, D. Houivet, J.M. Haussonne, M. Pollet, F. Roulland, and S. Marine!

Properties of FRAM Capacitors with Oxide Electrodes 311 K. Niwa, J.S. Cross, M. Tsukada, K. Kurihara, and N. Kamehara

Impedance Analysis of BME Dielectric Ceramics 319 D.F. Hennings, C. Hofer, R. Meyer, and C. Pithan

Electron Microscopy of Heterogeneous Interfaces in Cofired Noble and Base Metal Electrode Multilayer Ceramic Capacitors (MLCCS) 329

Q. Feng and C.J. McConville

Latex-Ferroelectric Composites 337 M.M. Sychov, O.A. Cheremisina, K.E. Bower, and S.M. Yousaf

Comparison of Bulk and Thin-Film Ferroelectrics—A Device Perspective... 345 D. Potrepka, S. Tidrow, and R. Polcawich

Direct-Charge Capacitor Modeling 353 M.M. Sychov, K.E. Bower, and S.M. Yousaf

Novel BaTi03-Ag Composites with Ultra-High Dielectric Constants Satisfying X7R Specifications 363

Z. Gui, R. Chen, X. Wang, and L. Li

Novel Board Material Technology for Next-Generation Microelectronic Packaging 371

N. Kumbhat, R Markondeya Raj, S. Hegde, R. V. Pucha, V. Sundaram, S. Hayes, S. Atmur, S. Bhattacharya, S.K. Sitaraman, and R.R. Tummala

High Power Piezoelectric Transformers—Their Applications to Smart Actuator Systems 383

K. Uchino, S. Priya, S. Ural, A. Vazquez Carazo, and T. Ezaki

The Processing and Electrical Properties of Sr(TixZr1.x)03 Compositions for High Voltage Applications 397

S.J. Lombardo and D.S. Krueger

Piezoelectric Ultrasonic Motors Using Bulk PZT and Utilizing Two Orthogonal Bending Modes of a Hollow Cylinder (Part 2) 405

S. Cagatay, B. Koc, and K. Uchino

Author Index 413 Keyword Index 415

Developments in Dielectric Materials and Electronic Devices · vii

Preface

The growth of materials research, technology development, and product innovation has been extraordinary during the last century. Our understanding of science and technology behind the electronic materials played a major role in satisfying societal needs by developing electronic devices for automotive, telecommunication, military and medical applications. Electronic technology still has an enormous role to play in the development of future materials for consumer applications. Miniaturization of electronic devices and improved system properties will continue during this century to satisfy the increased demands of our society particularly in the area of medical implant devices, telecommunications and automotive markets.

Materials societies like The American Ceramic Society understand their social responsibility. For the last many years, The American Ceramic Society organized several international symposium covering many aspects of the advanced electronic material systems by bringing together leading researchers and practitioners of electronics industry, university and national laboratories and published the proceedings of the conferences in the Ceramic Transactions Series, a leading up-to-date materials publication.

This volume contains a collection of selected papers from the international symposium: Advanced Electronic Materials and Devices, presented during the 106th Annual Meeting of The American Ceramic Society held in Indianapolis, Indiana, April 18-21, 2004. Thirty-eight invited and contributed papers are peer-reviewed and included in this volume.

We, the editors, acknowledge and appreciate the contributions of the speakers, conference session chairs, manuscript reviewers and Society officials for making this endeavor a successful one.

K. M. Nair R. Guo A.S. Bhalla S-I. Hirano D. Suvorov

Developments in Dielectric Materials and Electronic Devices · ix

Material Design, Synthesis & Properties

HYDROTHERMAL SYNTHESIS AND PROPERTIES OF SODIUM-DOPED BISMUTH TITANATE POWDERS

E.B. Slamovich, H. Xu, S. Mallick, W.F. Shelley H.Y Li, and K.J. Bowman Keramos Divison of Piezo Technologies School of Materials Engineering 5460 W. 84th Street Purdue University Indianapolis, IN 46268 501 Northwestern Avenue West Lafayette, IN 47907-1289

ABSTRACT Bismuth titanate was synthesized under hydrothermal conditions from an amorphous Bi-

Ti precursor gel. The gel was reacted under hydrothermal conditions at 160 and 180°C to form crystalline bismuth titanate. The gel crystallization kinetics increased with temperature, resulting in 100% crystalline bismuth titanate in 12 h at 180°C. WDS data indicated that sodium was incorporated into bismuth titanate during processing. TEM micrographs showed that the gel particles decomposed into 100-200 nm crystalline bismuth titanate particles during hydrothermal processing. The effect of sodium on the properties of bismuth titanate was investigated by examining Bt4Ti,Ol2 powders doped with 1-3 atomic % sodium. Sodium doping caused a structural transformation from the Bi4Ti30,2 to the Na^Bi^Ti^,, phase on heating to 1100 C in air. The transformation proceeded through the Na« 5Big ,Ti7027 configuration that has a structure with alternating two and three perovskite-like blocks interleaved with Bi202

2+ layers. Doping with sodium decreased the electrical conductivity of bismuth titanate.

INTRODUCTION Bismuth titanate is a member of the Aurivillius family of bismuth layer structure

perovskites [1]. The crystal structure of bismuth titanate consists of (Bi202)2+ layers interleaved

with perovskite units of (Βί,,,Τί,,Ο^,)2* along the c-axis, and lends itself to multiple phases such as Bi4Ti3Ol2 and Bi5Ti40,v Both of these phases exhibit piezoelectricity up to temperatures of 675 C. The applications for high temperature piezoelectric ceramics like bismuth titanate include ultrasonic sensors and accelerometers for use in the automotive, aerospace, and petroleum industries [2]. The utility of Bi4Ti,Ol2 is limited by its relatively large electrical conductivity in the polarization direction, which makes poling very difficult. [3] Experiments with doped Bi4Ti,Ol2 by Shulman et al. showed that the electrical conductivity of bismuth titanate increased with the addition of acceptor dopants and decreased with donor dopants. [4] In particular, Nb additions decreased conductivity by approximately 3 orders of magnitude. Their studies ruled out oxygen ionic conductivity as the dominant mechanism, instead suggesting that the data was consistent with p-type electronic conductivity.

Conventional processing of bismuth titanate is performed by the solid state reaction of mixed oxides requiring temperatures in excess of 900 C [5]. Chemical solution synthesis routes, including sol-gel and coprecipitation, enable the production of fine powders after calcining at temperatures of 750°C to form crystalline bismuth titanate [6,7]. Recently, hydrothermal processing has been used to synthesize bismuth titanate [8-10]. For example, Prasadarao and Komarneni synthesized Bi4Ti3012 at 240 C for 7 d using a mixture of bismuth and titanium

To the extent authorized under the laws of the United States of America, all copyright interests in this publication are the property of The American Ceramic Society. Any duplication, reproduction, or republication of this publication or any part thereof, without the express written consent of The American Ceramic Society or fee paid to the Copyright Clearance Center, is prohibited.

Developments in Dielectric Materials and Electronic Devices · 3

hydrous oxides [8], and Shi et al. synthesized Bi4Ti3012 at 240 C for 3 d by reacting Ti02 gels, formed from tetrabutyl titanate, with bismuth nitrate under alkaline conditions [9]

The first goal of the work described below was to develop a hydrothermal processing route to Na-doped bismuth titanate that requires lower processing times and temperatures compared to previous efforts. The approach used was to prevent the uncontrolled hydrolysis and precipitation of hydrous Bi203 and Ti02 using glacial acetic acid as a chelating agent [11,12]. The second goal was to assess the effect of Na-doping on the electrical conductivity of bismuth titanate. During the development of a hydrothermal processing protocol, conventionally processed Na-doped bismuth titanate was used for electrical property measurements and structure-property correlations.

EXPERIMENTAL PROCEDURE Processing and Characterization of Hydrothermally Derived Bismuth Titanate

0.05 M bismuth nitrate was first dissolved in glacial acetic acid, and an aqueous 3 M NaOH solution was added to adjust the solution pH to 3. Titantium n-butoxide was then added under constant stirring to bring the Bi to Ti ratio to 1.3:1. The resulting transparent solution was added drop wise into an aqueous 6 M NaOH solution cooled to approximately 0°C, causing the precipitation of a gel. The NaOH/gel suspension was subsequently transferred into a 125 ml teflon lined autoclave, and heated without stirring for various times at 160 and 180°C. The resulting powders were repeatedly washed by centrifugation and decantation with deionized water, and dried in an oven for 24 h at 80 C. Dried powders were ground using a mortar and pestle before further characterization.

The crystallization kinetics were investigated using x-ray diffraction (XRD) (D500, Siemens Analytical X-Ray Instruments Inc., Cherry Hill, NJ) by examining powder samples heated for different times. Powder samples were scanned over a two theta range of 20 -60 at 4 /min using Cu Ka radiation. Slower XRD scans were performed over a two theta range of 25 -37 at 1.2 /min for subsequent quantitative analysis. Powder crystallinity was quantified using the internal standard technique [13]. A calibration curve was obtained by mixing known masses of amorphous gel and fully crystallized bismuth titanate, and a constant 0.10 weight fraction of Si was added as an internal standard. A split Pearson 7 function was used to deconvolute the (109) reflection of the crystalline bismuth titanate from the broad peak of the amorphous phase.

Powder morphology was examined using transmission electron microscopy (TEM) (2000FX, JEOL Ltd., Tokyo, Japan) at 200 kV. Samples were prepared by dispersing powders in methanol using an ultrasonic bath, and collecting the powders on a carbon coated grid. The particle size distribution of the powders was measured (COULTER LS230, Coulter, Inc., Miami, FL) by dispersing 0.01-0.02 g of powder in 25 ml water and 1 ml of a dispersant (Darvan 821 A, R.T. Vanderbilt, Inc., Norwalk, CT). Compositional analysis was performed using wavelength dispersive spectroscopy (SX-50, Cameca Instruments Co., Stamford, CT). Before analysis, the powders were dry pressed into cylindrical compacts and coated with carbon. Quantitative analysis results were based on 10 points per sample.

Structure Characterization and Electrical Conductivity of Na-doped Bismuth Titanate Appropriate amounts of Bi203, Ti02 and Na2C03 powders were mixed to produce bismuth

titanate with a target stoichiometry of NaxBÍ5.xTi40I5, where x = 0.25, 0.50 and 0.75 (corresponding to nominally 1, 2 and 3 at% Na). The powders were mixed in a ball mill for 4 h with alumina grinding media. After ball milling the powders were dried at approximately 135 C

4 · Developments in Dielectric Materials and Electronic Devices

for 4 h. The powders were then screened to remove any large agglomerates and calcined in air at approximately 1100 C for 30 min using a covered alumina crucible heated in a batch-type furnace. Polyvinyl alcohol (PVA) was then added and the powders pressed to produce compacts with a green density of approximately 4 g/cm3. The pressed compacts were then dried at 75 C for about 24 h. For bisque firing, the compacts were heated at a rate of 60 C/h to 400 C and held at that temperature for 3-4 h. The temperature was then increased at the rate of 150 C/h to the final sintering temperature of 1100 C. Sintering was done in an oxygen rich atmosphere for 30 min in a covered alumina crucible. Thin discs (approximate thickness 0.5 mm) were then cut from the sintered compacts.

X-ray diffraction of the samples used Cu Ka radiation, and preliminary phase analysis was done using the MAUD Rietveld refinement program [14] assuming isotropic strain. Based on these results, a high resolution x-ray scan of selected samples was performed at the beamline X18A of the National Synchrotron Light Source, Brookhaven National Laboratory, NY, using 10 keV (wavelength 1.24Á) x-rays.

For TEM sample preparation, the compacts were thinned to approximately 200 μηι from which 3 mm diameter discs were cut. These were thinned further using a tripod polisher and finally placed on a copper grid and ion milled to make it electron transparent. High resolution TEM was done at Applied Materials' research lab, Santa Clara, CA, using 200 kV accelerating voltage. To reduce noise, some of the images were filtered by taking the Fourier transform, masking the spots, and taking the inverse Fourier transform.

Before poling, silver electrodes were applied to the samples by screen printing or using silver paint. The electrodes were dried in air for 1 h at 180 C resulting in highly adherent electrodes. Since bismuth titanate has a Curie temperature of approximately 675 C, the material was poled at 180-200 C. During poling the sample was clamped in a sample holder and immersed in silicone oil (Dow Corning dielectric grade 200). A DC potential of approximately 4000 V was applied across the sample, corresponding to a DC field of 8 kV/mm for a sample of nominal thickness 0.5 mm. The voltage was applied for 1 h after which the power source was turned off and the sample removed from the oil bath and allowed to air cool to room temperature. The samples were then washed and degreased using reagent grade acetone, and aged at 150 C for 2 h. After poling, the samples conductivity was measured by the DC two probe technique using a HP 34401A multimeter and assuming Ohmic behavior.

RESULTS AND DISCUSSION Hydrothermally Derived Bismuth Titanate

Crystallization of the amorphous bismuth-titanium gel occurred over a 50 h period at 160°C (Fig. 1). The characteristic reflections of crystalline bismuth titanate grew from the broad peak associated with the amorphous phase. Bismuth titanate crystallized more rapidly as the hydrothermal treatment temperature increased. [15] The rapid bismuth titanate crystallization rate may be attributed to the short diffusion distance between bismuth and titanium species mixed on the molecular scale in the gel particles. Previous efforts to process bismuth titanate hydrothermally have relied on the reaction of separate bismuth and titanium-containing phases. [8-9] The crystallization kinetics exhibited two regimes. First, an incubation period, in which no crystalline material was observed by XRD. It was difficult to quantify the time required to initiate crystallization since deconvoluting the amorphous and crystalline XRD reflections is problematic when the degree of crystallinity ranges from approximately 0-5%.

Developments in Dielectric Materials and Electronic Devices · 5

c

CO is 2

c

1 1 1

I (109)

Γ I I (110)

i I

L- . _L J_ _ J

I" Γ — T —

i 50h 1

A 30 h i

1 L A..,,,

1 1

J

~AJ

i Ί

20 25 30 35 40 45

2 theta 50 55 60

Figure 1: Crystallization of bismuth titanate at 160°C.

Incubation was followed by steady state growth of crystalline bismuth titanate. Analysis of the steady state regime was based on the Johnson-Mehl-Avrami equation [16]:

ln[-ln(l - / ) ] - Inr + mIn/ (1)

where / is the fraction crystallized at time t, r a rate constant that depends on the frequency of nucleation and the growth rate, and m is a constant that may be related to the reaction mechanism. Fitting the data in the range of 15-75% crystallinity to equation 1 yields m values of 1.8 and 2.9 for 160°C and 180°C respectively (Fig. 2). Both values are consistent with nucleation and growth mechanisms of the type reviewed by Hulbert [17].

After hydrothermal processing for 5 h at 160°C, the gel particles were spherical and had a submicrometer average size (Fig. 3a). Nucleation and growth of bismuth titanate during hydrothermal processing occurred within the gel particles resulting in a composite of crystallizing bismuth titanate particles in a gel matrix (Fig. 3b). The growing particles were highly anisometric, and localized stacking of the bismuth titanate platelets suggests the possibility of a crystallographic relationship during crystallization. During later stages of crystallization, the volume fraction of gel was no longer sufficient to hold the crystalline platelets together, resulting in the decomposition of the gel particles into discrete 100-200 nm crystallites after 50 h (Fig. 3c). This scenario is supported by particle size measurements (Fig. 4). After 3 h at 160°C the gel particles had a mean size of approximately 0.50 μπι, and after 50 h the mean particle size had decreased to approximately 100 nm. Data collected at 180°C displayed similar trends. Therefore, despite the significantly different slope of the kinetic data in Figure 2 there appears to be no difference in the reaction mechanism. Previous applications of the Johnson-Mehl-Avrami to examine hydrothermal synthesis of barium titanate and lead titanate have

6 · Developments in Dielectric Materials and Electronic Devices

T=180°C, m=2.9/

T=160°C,m=1.8

9.5 10 10.5 11 11.5 12

In(time) Figure 2: Johnson-Mehl-Avrami analysis of bismuth titanate crystallization kinetics.

Figure 3: TEM micrographs of bismuth titanate powders after hydrothermal processing at 160°C for a) 5, b) 20 and c) 50 h.

Developments in Dielectric Materials and Electronic Devices · 7

suggested that two kinetic regimes exist beyond the incubation period. [18,19] In both cases the metal cations were initially in discrete phases. In this study both the kinetic data and microstructural observations suggest that only one kinetic regime appears to exist after incubation. Perhaps this is due to the molecular scale mixing of the metal cations.

i 1 r

j | L 0 0.5 1 1.5 2

Particle Size (μΓη)

Figure 4: Bismuth titanate particle size distribution after hydrothermal processing at 160°C for 3 and 50 h.

Quantitative chemical analysis via WDS (Table I) showed that the composition of the crystalline bismuth titanate powder, formed after 50 h at 160°C, was close to that of the precipitated gel particles after 3 h of hydrothermal treatment at 160°C. The standard deviation of the data dropped significantly during crystallization suggesting greater compositional homogeneity in the crystalline product. Also, the sodium content decreased with time, an indication that the crystalline phase had a lower solubility for sodium. Within the margin of error for WDS it was not possible to determine whether the powder was composed of either BÍ4TÍ3O12 or BÍ5TÍ4O15, or was mixture of these phases.

Table I: WDS of Bismuth Titanate Powders Processed at 160°C.

Time (h)

3

50

Na (atm.%)

Avg Std.Dev.

3.59 1.15

0.95 0.07

Bi (atm.%)

Avg Std.Dev.

19.77 1.84

20.64 0.06

Ti (atm.%)

Avg Std.Dev.

15.07 0.98

15.66 0.07

O (atm.%)

Avg Std.Dev.

61.58 0.29

62.75 0.04

8 · Developments in Dielectric Materials and Electronic Devices

Na-doped Bismuth Titanate Synthesized by Solid-State Reaction After sintering at 1100°C the relative density, as measured using Archimedes' principle,

of the undoped bismuth titanate was 94%, and the densities of Na-doped samples ranged from 87-88%. Electrical measurements showed that doping bismuth titanate with 1 at.% sodium decreased conductivity by four orders of magnitude (Fig. 5). Increasing the sodium content further reduced electrical conductivity and facilitated poling. Regardless whether sodium substitutes for bismuth or titanium, it should be considered to be an acceptor dopant. Research by Shulman et al. concluded that bismuth titanate exhibits p-type conductivity, and showed that acceptors like strontium and calcium increase electrical conductivity. [4] Therefore, one should expect sodium doping to increase bismuth titanate conductivity. The observation of the opposite trend suggests that either sodium exhibits anomalous acceptor behavior, or there are factors other than defect chemistry influencing electrical conductivity.

1(T

107

'•p 10β

Ü

Con

duct

ivity

(Ohm

· 9

9 9

3 5

—

O

«0

1013

10·"

i

-—

— J _

•

•

• 1 _

, , , . · · · ·

• · 0%Na

1at%Na . * • •

. · · # #

2 at.% Na

3 at. % Na 1 1 1

—i r~

• · ·

• •

•

_J 1_

— · 1

H

J •

•

J 120 130 180 190 140 150 160 170

Temperature (°C) Figure 5: Electrical conductivity of bismuth titanate as a function of sodium content.

Synchrotron XRD data was analyzed using the MAUD Rietveld refinement software to determine the bismuth titanate phase content. Structural models for Bi4Ti3Ol2, Na^Bi^T^O^ and Nao5oBi8 5Ti7027

w e r e u s e^ a s the basis for data refinement. Bi4Ti3Ol2 phase content decreased monotonically with increasing sodium content, and was replaced by the Nao.5oBi4(5Ti40|s and Na050Bi85Ti7O27 structures (Fig. 6). [20] Na^Bi^/r^O,, differs from the Bi4Ti30,2 structure by the inclusion of a fourth perovskite unit cell between the (Bi202)

2+ layers. Aliovalent doping, in this case with sodium, fulfills the charge neutrality requirement. The Na,,»Big 5Ti7027 structure combines layers of the Bi4Ti3Ol2 and Na^Bi^T^O^ structures as shown by high resolution TEM of a 3 at.% Na-doped sample (Fig. 7). Note that the slightly thicker layers in figure 7 reflect the extra perovskite block expected from the Ν%50Βί4 5Ti4Ol5

structure. It is possible that Na^Bi^T^O^, is a distinct structure, or that it represents the interfacial region between Bi4Ti,Ol2 and Nao5oBi45Ti40,5 grains, and there is a sufficient volume fraction of the interfacial region to influence the x-ray diffraction data. Although a distinct

Developments in Dielectric Materials and Electronic Devices · 9

100

4-3-12 Structure

9-7-27 Structure

2 3 4 Atomic % Na

Figure 6: Bismuth titanate phase distribution as a function of sodium concentration.

Figure 7: High resolution TEM micrograph of the Na,j 5oBi8 5Ti7027 structure.

10 · Developments in Dielectric Materials and Electronic Devices

Nao50Bi85Ti7027 structure has not been reported, Boullay et al. observed long-range order in the intergrowth structure in the Bi3TiNb09 - Bi4Ti3Ol2 system. [21] Therefore, it is possible that Nao soBig 5Ti7027 is not an interfacial region, but rather represents a distinct mixed layer structure. [20]

Connections between the electrical conductivity behavior and changing crystal structure as a function of sodium content are currently being investigated. The different structures have different intrinsic conductivities, and there are dislocation-like defects and stacking faults associated with the layered structures. However, preliminary calculations suggest that these structural effects appear to have a much smaller influence on electrical conductivity relative to point defects introduced via doping.

SUMMARY Coprecipitation of bismuth-titanium gel particles enabled hydrothermal processing of

bismuth titanate at 160°C in 50 h. Increasing the processing temperature to 180°C reduced the processing time to 12 h. Bismuth titanate crystallization occurred within the micrometer-size gel particles, and the gel particles eventually decomposed into 100-200 nm crystallites. Na-doping significantly lowered the electrical conductivity of bismuth titanate, possibly due to the formation of defects associated with structural transformations in the powder.

ACKNOWLEDGEMENTS The authors wish to acknowledge the Keramos division, Piezo Technologies, Indianapolis,

IN, for their assistance in sample preparation. We are also grateful to Hong Zhang of Applied Materials Inc., Santa Clara, CA., for assistance with TEM specimen preparation and high resolution imaging.

Financial support for this project was provided by the Indiana 21st Century fund. Research was carried out in part at the National Synchrotron Light Source, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Division of Materials Sciences and Division of Chemical Sciences, under Contract No. DE-AC02-98CH10886.

REFERENCES 1. B. Aurivillius, "Mixed Oxides with Layer Lattices," Arkiv for Kemi, 1 [54] 463-499

(1949). 2. D.A. Stubbs and R.E. Dutton, "An Ultrasonic Sensor for High-Temperature Materials

Processing," JOM, 48 [9] 29-31 (1996) 3. A. Fouskova and L.E. Cross, "Dielectric Properties of Bismuth Titanate," J. Appl. Phys.,

41 [7] 2834-38 (1970). 4. H.S. Shulman, M. Testorf, D. Damjanovic, and N. Setter, "Microstructure, Electrical

Conductivity, and Piezoelectric Properties of Bismuth Titanate," J. Am. Ceram. Soc, 79 [12] 3124-28(1996).

5. B. Jaffe, W. R. Cook and H. Jaffe, Piezoelectric Ceramics, Academic Press, New York, NY (1971).

6. M. Toyoda, and D.A. Payne, "Synthesis and Characterization of an Acetate-Alkoxide Precursor for Sol-Gel Derived Bi4Ti3012," Mater. Lett. 18 [1-2] 84-88 (1993).

7. A.M. Umabala, M. Suresh and A.V. Prasadarao, "Bismuth Titanate from Coprecipitated Stoichiometric Hydroxide Precursors," Mater. Lett., 44 175-180 (2000).

Developments ¡n Dielectric Materials and Electronic Devices · 11

8. A.V. Prasadarao, and S. Komarneni, "Hydrothermal Synthesis of Bismuth Titanate"; pp. 923-925 in ISAF'96, Vol.2, Proceedings of the Tenth IEEE International Symposium on Applications of Ferroelectrics (East Brunswick, NJ, August 1996). Edited by B. M. Kulwicki, A. Amin and A. Safari. The Institute of Electrical and Electronic Engineers (IEEE) Ultrasonics, Ferroelectrics and Frequency Control Society, Piscataway, NJ, 1996.

9. Y. Shi, C. Cao and S. Feng, "Hydrothermal Synthesis and Characterization of Bi4Ti3012," Mater. Lett., 46 [5] 270-273 (2000).

10. M.M. Lencka, M. Oledzka and R.E. Riman, "Hydrothermal Synthesis of Sodium and Potassium Bismuth Titanates," Chem. Mater., 12 [5] 1323-1330 (2000).

l l .J. Livage, C. Sanchez, M. Henry and S. Doeuff, "The Chemistry of the Sol-Gel Process," Solid State Ionics, 32 [3] 633-638 Part 2 (1989).

12. C. Sanchez, J. Livage, M. Henry and F. Babonneau, "Chemical Modification of Alkoxide Precursors," J. Non-Cryst. Solids, 100 [1-3] 65-76 (1988).

13. R. Jenkins and R.L. Snyder, "The Internal Standard Method of Quantitative Analysis," pp. 370-374 in Introduction to X-ray Powder Diffraction, Wiley, New York, 1996.

14. L. Lutterotti, S. Matthies, H.R. Wenk, "MAUD (Material Analysis Using Diffraction): A User Friendly {Java} Program for{Rietveld} Texture Analysis and More," Proceeding of the Twelfth International Conference on Textures of Materials (ICOTOM-12U 1 1599 (1999).

15. H. Xu, K.J. Bowman and E.B. Slamovich, "Hydrothermal Synthesis of Bismuth Titanate Powders," J. Am. Ceram. Soc., 86 [10] 1815-17 (2003).

16. M.J. Avrami, "Kinetics of Phase Change, II. Trans formation-Time Relations for Random Distribution of Nuclei," J. Chem. Phys., 8 212-224 (1946).

17. S.F. Hulbert, "Models for Solid-State Reactions in Powdered Compacts: A Review," J. Brit. Ceram. Soc., 6 [1] 11-20 (1969).

18. J.O. Eckert Jr., C.C. Hung-Houston, B.L. Gersten, M.M. Lencka and R.E. Riman, "Kinetics and Mechanisms of Hydrothermal Synthesis of Barium Titanate," J. Am. Ceram. Soc, 79 [11] 2929-39 (1996).

19. G.A. Rosetti Jr., D.J. Watson, R.E. Newnham and J.H. Adair, "Kinetics of the Hydrothermal Crystallization of the Perovskite Lead Titanate," J. Crys. Growth, 116, 251-59 (1992).

20. S. Mallick, K.J. Bowman, E.B. Slamovich, A.H. King and J.L. Jones, "Structural Transformations in Bismuth Titanates," to be published in Ceramic Transactions.

21. P. Boullay, G. Trolliard, D. Mercurio, J.M. Perez-Mato, L. Elcoro, "Towards a Unified Approach to the Crystal Chemistry of Aurivillius-Type Compounds - 1 . The Structure Model," J. Sol. State Chem., 164,261 (2002).

12 · Developments in Dielectric Materials and Electronic Devices

NOVEL PROCESSING OF FUNCTIONAL CERAMIC FILMS BY CSD WITH UV IRRADIATION

K. Kikuta, K. Noda, R. Kono, T. Yamaguchi, K. Morita *, K. Takagi*, and S. Hirano Department of Applied Chemistry 'Department of Crystalline Materials Science Nagoya University Nagoya 464-8603 Japan

ABSTRACT

In order to prepare functional ceramic films, the chemical stability and photo-reactivity of precursor compounds must be appropriately controlled by changes in the molecular structure. Functional ceramic film processing using the chemical solution deposition method (CSD) with UV irradiation was studied. A new light source, the Y-line lamp, was used for the photoreaction of the ceramic precursor films. It was found that this process was effective in preparing amorphous titania films with a high refractive index, and could also be used as an intermediate treatment for making high quality dielectric films.

INTRODUCTION

Recently, demands for low temperature and new patterning process of ceramics have increased ,*5. Among these processes, the chemical solution deposition method (CSD) is a good one in preparing functional ceramic films, such as ferroelectrics for non-volatile memory devices.6*8 In the present study, we used CSD combined with UV irradiation (UV-CSD) to develop a process that created ceramic coats on inorganic substrates like glass and organic polymers at lower temperatures. This process is simple and does not require expensive vacuum production facilities. It can be used in the pre-heating process for removal of organic components because the films treated with UV irradiation do not include organic components derived from the organic ligands. We previously reported the basic process synthesizing oxide and non-oxide ceramic films9"11. In this paper, we discuss the procession of functional ceramic films using the UV lamp, which can cause sufficient photoreaction in a large area similar to the photo-curing process of organic polymers in the VLSI industries.

Several approaches were attempted in this study: (1) to make a photo-curable zirconia precursor, (2) to apply this process to make an amorphous titania film on an organic substrate, and (3) to improve the electric properties of crystalline BÍ4TÍ3O12 film. These approaches were investigated using a new light source and molecular structure modification of the ceramic precursors.

EXPERIMENTAL PROCEDURE

Figure 1 illustrates a typical process. A starting compound such as metal alkoxide was dissolved into an organic solvent like ethanol. The organic additive was then mixed into the solution to form

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Developments in Dielectric Materials and Electronic Devices «13

a stable and photo-reactive ceramic precursor. The amount of added alkanolamine was one half of the alkoxy group for the starting titanium alkoxide. The starting compounds and chemical additives are summarized in Table 1.

| Metal Alkoxide || Alkanolamine | 1 Dtethanolamine

in Alcohol Dry Ethanol

Stirring

1 1 | Precursor Solution |

indryNj

| Precursor Solution |

Coating

| UV Irradiation

1 Leaching for Patterning)

1 | Amorphous Oxide Film | I 4

Crystallization

Ceramic Film

Fig.l. Preparation of ceramic film using UV irradiation

Table 1. The starting compounds and additives used for preparation of the precursor solutions

STARTING COMP. CHEMICAL ADDITIVES SOLVENT UV LAMP

Diethanolamine Ethanol

Ethanol

Ti Isopripoxide Zr Isopropoxide 2,6-pyridinedimethanol

(PDM)

Bi Amyioxide Acethyacetone 2-methoxyethanol Ti Isopropoxide

UHML, Y-Line

UHML

Y-Line

Ceramic precursor films were prepared on substrates by spin coating at a rate of 2000 rpm. The prepared films were irradiated with two kinds of UV lamps, an Ultra-high pressure mercury lamp and a Y-line lamp (Ushio Co. Ltd., Optical Module X). The former is a popular light source for the photo-curing process of organic polymers and the latter emits strong UV light below 250 nm, as shown in Fig. 2. The photoreaction process was monitored by UV-Vis (Hitachi, U-3410) and FT-IR (Jasco, FT/IR-610) spectrometers, and the surface profile of the film was observed by AFM (Olympus, NV2000). The refractive index was characterized by ellipsometry. Ferroelectric properties were characterized by the ferroelectric test system (Radiant Technologies, RT-66A). In order to elucidate the reaction, the films were also examined by ESCA (Jeol, JPS-9000) to check the depth profile of the spectra on the metal species. Ferroelectric properties were also characterized by ferroelectric test system (Radiant Technologies, RT-66A).

14 · Developments in Dielectric Materials and Electronic Devices

200 220 240 260 280 Wavelength/nm

300

Fig. 2. Emission spectrum of the Y-line lamp

RESULTS AND DISCUSSION

Chemical Stability of the Precursor Solutions and Selection of the UV Lamp Several kinds of metal precursor solutions were successfully synthesized by adding chemicals

such as diethanolamine into a metal alkoxide solution. This preferentially coordinated to the metal ions by exchanging alkoxy groups and suppressing the hydrolysis as follows:

M(OR)n + HN(C2H4OH)2 = M(OR)n-2(HNC2H40)2 + 2ROH. (1)

However, these precursor films have different absorption properties that depend on the metal types. This leads to the selection of the applied UV sources, as summarized in Fig. 3.

φ 80 o c CO

¿5 60

ε

Zr

/ /

r*""*"̂

Ti

Y-LLamp

UHML

Í 200 A 250 300 350 400

I Wavelength (nm) 174 nm 222 nm

Excimer Lamp

Fig. 3. UV-Vis spectra of ceramic precursor films prepared by the addition of diethanolamine

Developments in Dielectric Materials and Electronic Devices · 15

The optical transparent regions of these precursor films were related to the metal oxide band structures. The precursor films of a semi-conductive oxide such as titania are easily reacted by longer UV light from UHML, although Sn and Zr precursors do not. The Y-line lamp is a unique light source having strong UV light at a wavelength region shorter than 250 nm, as shown in Fig. 2. This lamp is considered to be more effective than the common mercury lamps for photoreaction and the removal of organics components like the added alkanolamine group.

Modification of the Molecular Structure of Zirconium Precursors In this study, one improvement of the procession was by the chemical modification of the

precursor with organic additives. As mentioned above, zirconium precursor with diethanolamine is usually transparent in the UV regions emitted by UHML. In order to generate a precursor photoreaction by UHML irradiation, several aromatic alkanolamines and pyridine alcohols, such as 2,6-pyridinedimethanol (PDM), are added to the solution to make a zirconium precursor (Fig. 4). It was confirmed that the addition of PDM was effective in making a homogeneous and stable zirconium solution similar to the co-addition process reported by Kikuta et αίη The prepared Zr precursor film is stable in certain air conditions like moisture, and can be cured by irradiation with UHML. It was observed that the absorption at 275 nm assigned to the pyridine ring of PDM became weaker in accordance to the irradiation time, as can be seen in Fig. 5. It was also possible to obtain a fine pattern of zirconia by UV irradiation through a photomask, followed by leaching with a solvent and a heating process, as shown in Fig. 6. Many ceramic fine pattern types have been synthesized via the process shown in Table 2.

Aromatic Alkanolamine

PhDEA

<f yN(CH2CH2QH)2

Phenyldiethanolamine HPA

\ _ \ N(CH2CHCH3)2

OH NJV-Bis(2-hydraxypropyt)aniline

Pyridine alcohol

AE o NHCH2CH2OH

2-A nilinoethanol

PE

CH2CH2OH

2-pyridineethanol

PDM , CH20H

Γ» CH20H

2,4-pyridinedimethanot

Fig. 4. Organic additives used for the preparation of photo-reactive precursors

16 · Developments in Dielectric Materials and Electronic Devices

1.5

H

0.5

\ j

1 ■ i i i > i

0 ndn. Λ 1

A 5 i M i o r v5

^ r " ^ r ~ n » H 200 250 300 350

Wavelength (nm) 400

Fig. 5. Change in the UV spectra of Zr-PDM precursor films by UV irradiation (UHML)

Table 2. Ceramic fine pattern prepared by UV curing of a precursor film with UHML

Chemical Additive Prepared Ceramic Pattern

Addition of Alkylamlne (ex. Diethanolamine) T102, (SnOJ, TIN

Aromatic Alkanolamine

or Pyridinalcohol

(ex. Phenyldiethanolamine)

Sn02, N205, Zr02,

Fig. 6. Zirconia fine pattern prepared from Zr-PDM

Developments in Dielectric Materials and Electronic Devices · 17

φ υ c

c

ε

After 5 min. irradiation

\ Precursor film

\ Λ \Λ""""\

Γ\

1000 Fig. 7. Change

Ti-DEA

4000 3000 2000

Wavenumber (cm1)

irradiation with the Y-line lamp

in the IR spectra of precursor films by UV

Preparation of An Amorphous Titanium Oxide Film with a High Refractive Index on Organic Polymer Substrates

Crystalline titanium oxide films have been synthesized for many applications, for example, as a photo-catalyst, an anti-clouding mirror, and other optical applications. Film synthesis was achieved by the titanium precursor film photoreaction using the Y-line lamp. Figure 7 shows the spectra changes in the IR region, which reveals that the organic components can be removed within 5 minutes. The XPS spectra on the Ti2P and Cis of the prepared film shown in Fig. 8 also revealed that the film is homogeneous and very similar to that of crystalline titania and that the remaining carbon content is quite small. After a 5-minute irradiation, the refractive index of the prepared titania film increased to 2.1, which is more than that of the film heated at 450°C12.

c Φ

480 470 460 450

Binding Energy (eV) 440

'IS

Inside

280 290

Binding Energy (eV) 300

Fig. 8. XPS spectra of an amorphous titania film at room temperature

Application of UV Treatment for Making a Ferroelectric Film

18 · Developments in Dielectric Materials and Electronic Devices