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Chemically prepared Pb(Zr{sub 0.951}Ti{sub 0.949}){sub 0.982}Nb{sub 0.018}O{sub 3} ceramics were fabricated that were greater than 95% dense for sintering temperatures as low as 925 C. Achieving high density at low firing temperatures permitted isolation of the effects of grain size, from those due to porosity, on both dielectric and pressure induced transformation properties. Specifically, two samples of similar high density, but with grain sizes of 0.7 {micro}m and 8.5 {micro}m, respectively, were characterized. The hydrostatic ferroelectric (FE) to antiferroelectric (AFE) transformation pressure was substantially less (150 MPa) for the lower grain size material than for the larger grain size material. In addition, the dielectric constant increased and the Curie temperature decreased for the sample with lower grain size. All three properties: dielectric constant magnitude, Curie point shift, and FE to AFE phase transformation pressure were shown to be semi-quantitatively consistent with internal stress levels on the order of 100 MPa.

Small, reliable chemical sensors are needed for a wide range of applications, such as weapon state-of-health monitoring, nonproliferation activities, and manufacturing emission monitoring. Significant improvements in present surface acoustic wave sensors could be achieved by developing a flexural plate-wave (FPW) architecture, in which acoustic waves are excited in a thin sensor membrane. Further enhancement of device performance could be realized by integrating a piezoelectric thin film on top of the membrane. These new FPW-piezoelectric thin film devices would improve sensitivity, reduce size, enhance ruggedness and reduce the operating frequency so that the FPW devices would be compatible with standard digital microelectronics. Development of these piezoelectric thin film // FPW devices requires integration of (1) acoustic sensor technology, (2) silicon rnicromachining techniques to fabricate thin membranes, and (3) piezoelectric thin films. Two piezoelectric thin film technologies were emphasized in this study: Pb(Zr,Ti)O{sub 3} (PZT) and AlN. PZT thin films were of sufficient quality such that the first high frequency SAW measurements on PZT thin films were measured during the course of this study. Further, reasonable ferroelectric properties were obtained from PZT films deposited on Si surface micromachined FPW device membranes. Fundamental understanding of the effect of nanodimension interfacial layers on AlN thin film domain configurations and piezoelectric response was developed. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US Department of Energy under contract DE-AC04-94AL85000.

A chemical solution powder synthesis technique has been developed that produces fine uniform powders of lead magnesium niobate (PMN) with 60 to 80 nm crystallite size. The synthesis technique was based on the dissolution of lead acetate and alkoxide precursors in acetic acid followed by precipitation with oxalic acid/propanol solutions. Lead magnesium niobate ceramics fabricated from these chemically derived powders had smaller, more uniform grain size and higher dielectric constants than ceramics fabricated from mixed oxide powders that were processed under similar thermal conditions.

A chemical solution powder synthesis technique has been developed that produces fine, uniform powders of lead magnesium niobate (PMN) with 60 to 80 nm crystallite size. The synthesis technique was based on the dissolution of lead acetate and alkoxide precursors in acetic acid followed by precipitation with oxalic acid/propanol solutions. Lead magnesium niobate ceramics fabricated from these chemically derived powders had smaller, more uniform grain size and higher dielectric constants than ceramics fabricated from mixed oxide powders that were processed under similar thermal conditions. Chem-prep PMN dielectrics with peak dielectric constants greater than 22,000 and polarizations in excess of 29 μC/cm2 were obtained for 1100 °C firing treatments. Substantial decreases in dielectric constant and polarization were measured for chemically prepared PMN ceramics fired at lower temperatures, consistent with previous work on mixed oxide materials.

Discharge capacitors were designed based on materials with antiferroelectric (AFE) to ferroelectric (FE) field enforced transitions that had 10 times the capacitance of relaxor ferroelectric or state of the art BaTiO{sub 3} materials in the voltage range of interest. Nonlinear RLC circuit analysis was used to show that the AFE to FE materials have potentially more than 2 times the peak discharge current density capability of the BaTiO{sub 3} or lead magnesium niobate (PMN) based relaxor materials. Both lead lanthanum zirconium tin titanate (PLZST) AFE to FE field enforced phase transition materials and PMN based relaxor materials were fabricated and characterized for Sandia`s pulse discharge capacitor applications. An outstanding feature of the PLZST materials is that there are high field regimes where the dielectric constant increases substantially, by a factor of 20 or more, with applied field. Specifically, these materials have a low field dielectric constant of 1,000, but an effective dielectric constant of 23,000 in the electric field range corresponding to the FE to AFE transition during discharge. Lead magnesium niobate (PMN) based relaxor materials were also investigated in this project because of their high dielectric constants. While the PMN based ceramics had a low field dielectric constant of 25,000, at a field corresponding to half the charging voltage, approximately 13 kV/cm, the dielectric constant decreases to approximately 7,500.

A novel technique has been developed for the synthesis of homogeneous, weakly agglomerated highly filterable Pb(Zr, Ti)O{sub 3} (PZT) powders. PZT 95/5 based ceramics were fabricated from these powders to determine interrelationships among microstructure, dielectric properties and pressure induced ferroelectric (FE) to antiferroelectric (AFE) phase transitions. Initial measurements indicate that microstructure has a substantial effect on hydrostatic depoling characteristics. While smaller grain size materials and higher switching pressures, subtleties in microstructure, which may include entrapped porosity, resulted in a more diffuse depoling characteristic. In addition, greater than 90% dense materials were obtained at process temperatures as low at 900{degrees}C. were only 30% of the values of PZT 95/5 fired at 1300{degrees}C, the dielectric constants of the 900{degrees}C materials were almost a factor of two higher. Backscattered electron Kikuchi pattern analysis determined that adjacent, nonlinear, irregularly shaped domain structures observed by electron channel imaging were 109{degrees} domains.

Ferroelectric PbTiO{sub 3} (PT) and Pb(Zr{sub x}Ti{sub 1{minus}x})O{sub 3} (PZT) thin films have been deposited on (100) MgO and (111) Pt/SiO{sub 2}/(100)Si substrates by using a novel single-solid-source metalorganic chemical vapor deposition (MOCVD) technique. The new technique uses a powder delivery system to deliver the mixed precursor powders directly into a hot vaporizer from room temperature, therefore, avoiding any problems associated with polymerization or decomposition of the precursors before evaporation. The technique simplifies MOCVD processing significantly and can improve process reliability and reproducibility. The deposited PT and PZT films have a perovskite structure and are highly oriented with respect to the substrate. With improvement of process control, systematic studies of film evolution under various growth conditions have been carried out. Effects of substrate, substrate temperature, system vacuum, and precursor ratios in the mixture on film microstructure and properties will be presented in this paper.

Oxide electrode technology is investigated for optimization of Pb(Zr,Ti)O{sub 3} (PZT) thin film capacitor properties for high density nonvolatile memory applications. PZT thin film capacitors with RF sputter deposited La{sub 0.5}Sr{sub 0.5}CoO{sub 3} (LSCO) electrodes have been characterized with respect to the following parameters: initial dielectric hysteresis loop characteristics, fatigue performance, microstructure and imprint behavior. Our studies have determined that the fatigue of PZT capacitors with LSCO electrodes is less sensitive to B site cation ratio and underlying electrode stack technology than with RuO{sub 2} electrodes. Doping PZT thin films with Nb (PNZT) improves imprint behavior of LSCO//PZT//LSCO capacitors considerably. We have demonstrated that PNZT 4/30/70 // LSCO capacitors thermally processed at either 550{degrees}C or 675{degrees}C have almost identical initial hysteresis properties and exhibit essentially no fatigue out to approximately 10{sup 10} cycles.

For PZT films deposited on Pt coated substrates, remanent polarization is a monotonic function of thermal expansion of the substrate, a result of 90{degree} domain formation occurring as the film is cooled through the transformation temperature. PZT film stress in the vicinity of the Curie point controls 90{degree} domain assemblages within the film. PZT films under tension at the transformation temperature area-domain oriented; whereas, films under compression at the transformation temperature are c-domain oriented. From XRD electrical switching of 90{degree} domains is severely limited. Thus, formation of these 90{degree} domains in vicinity of the Curie point is dominant in determination of PZT film dielectric properties. Chemically prepared PZT thin films with random crystallite orientation, but preferential a-domain orientation, have low remanent polarization (24 {mu}C/cm{sup 2}) and high dielectric constant (1000). Conversely, PZT films of similar crystalline orientation, but of preferential c-domain orientation, have large remanent polarizations (37 {mu}C/cm{sup 2}) and low dielectric constants (700). This is consistent with single-crystal properties of tetragonally distorted, simple perovksite ferroelectrics. Further, for our films that grain size - 90{degree} domain relationships appear similar to those in the bulk. The effect of grain size on 90{degree} domain formation and electrical properties are discussed.

Factors that control phase evolution, microstructural development and ferroelectric domain assemblage are evaluated for chemically prepared lead zirconate titanate (PZT) thin films. Zirconium to titanium stoichiometry is shown to strongly influence microstructure. As Ti content increases, there is an apparent enhancement of the perovskite phase nucleation rate, grain size becomes smaller, and the amount of pyrochlore phase, if present, decreases. While the pyrochlore matrix microstructure for near morphotropic phase boundary composition thin films consists of two interpenetrating nanophases (pyrochlore and an amorphous phase); the pyrochlore microstructure for PZT 20/80 films deposited on MgO substrates is single phase and consists of 10 nm grains. Zirconium to titanium stoichiometry also has a substantial influence on process integration. Near morphotropic phase boundary films exhibit extensive reaction with underlying Ti02 diffusion barriers; conversely, there is no chemical reaction for identically processed PZT 20/80 thin films. We have attempted to directly correlate the optical quality of PZT thin films to the following microstructural features: 1) presence of a second phase, 2) domain orientation, and 3) nanometer surface morphology. © 1994, Taylor & Francis Group, LLC. All rights reserved.

The effects of orientation and stress on chemically prepared Pb(Zr,Ti)O3 (PZT) film properties have been determined. Systematic modification of the underlying substrate technology has made it possible to fabricate suites of films that have various degrees of orientation at a constant stress level, and to fabricate films that are in different states of stress but have similar orientation. Highly oriented films of the following compositions have been fabricated: PZT 60/40, PZT 40/60, and PZT 20/80. Remanent polarizations ( approximately=60 mu C/cm2) greater than those of the best bulk polycrystalline ferroelectrics were obtained for PZT 40/60 films that were under compression and highly.

We have systematically varied processing parameters to fabricate PZT 53/47 thin films. Polycrystalline PZT thin films were fabricated by spin depositing Pt coated SiO{sub 2}/Si substrates with alkoxide solutions. Our study focused on two process parameters: (1) heating rate and (2) excess Pb additions. We used rapid thermal processing techniques to vary heating rates from 3{degree}C/min to 8400{degree}C/min. Films were characterized with the following excess Pb additions: 0, 3, 5, and 10 mol %. For all process variations, films with greater perovskite content had better ferroelectric properties. Our best films were fabricated using the following process parameters: an excess Pb addition of 5 mol %, a heating rate of 8400{degree}C/min and annealing conditions of 700{degree}C for 1 min. Films fabricated using these process conditions had a remanent polarization of 0.27 C/m{sup 2} and a coercive field of 3.4 MV/m. 12 refs., 4 figs.

We report on the first ferroelectric measurements of chemically prepared KNbO/sub 3/ thin films. Polycrystalline KNbO/sub 3/ thin films were fabricated by dip coating substrates with methanolic solutions of potassium hydroxide and niobium ethoxide. Perovskite KNbO/sub 3/ was obtained for both bulk gels and films by using 800/degree/C firing treatments. For films, the intermediate temperature processing schedule was critical for the complete conversion of low temperature phases to perovskite KNbO/sub 3/. Raman spectroscopy and x-ray diffraction analysis confirmed that properly processed films possessed the orthorhombic distortion of the perovskite structure at room temperature. In response to a 1 kHz, sinusoidal field of 300 kV/cm amplitude, we measured the following ferroelectric properties: (1) a remanent polarization of 4.5 ..mu..C/cm/sup 2/, (2) a spontaneous polarization of 8.3 ..mu..C/cm/sup 2/, and (3) a coercive field of 55 kV/cm.