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Predictions and measurements of the effect of biaxial strain on the properties of epitaxial ferroelectric thin films and superlattices are reviewed. Results for single-layer ferroelectric films of biaxially strained SrTiO3, BaTiO3, and PbTiO3 as well as PbTiO3/SrTiO3 and BaTiO3/SrTiO3 superlattices are described. Theoretical approaches, including first principles, thermodynamic analysis, and phase-field models, are applied to these biaxially strained materials, the assumptions and limitations of each technique are explained, and the predictions are compared. Measurements of the effect of biaxial strain on the paraelectric-to-ferroelectric transition temperature (TC) are shown, demonstrating the ability of percent-level strains to shift TC by hundreds of degrees in agreement with the predictions that predated such experiments. Along the way, important experimental techniques for characterizing the properties of strained ferroelectric thin films and superlattices, as well as appropriate substrates on which to grow them, are mentioned.

Out-of-phase boundaries (OPBs) are translation boundary defects characterized by a misregistry of a fraction of a unit cell dimension in neighboring regions of a crystal. Although rarely observed in the bulk, they are common in epitaxial films of complex crystals due to the physical constraint of the underlying substrate and a low degree of structural rearrangement during growth. OPBs can strongly affect properties, but no extensive studies of them are available. The morphology, structure, and nucleation mechanisms of OPBs in epitaxial films of layered complex oxides are presented with a review of published studies and new work. Morphological trends in two families of layered oxide phases are described. The atomic structure at OPBs is presented. OPBs may be introduced into a film during growth via the primary mechanisms that occur at film nucleation (steric, nucleation layer,a-bmisfit, and inclined-cmisfit) or after growth via the secondary nucleation mechanism (crystallographic shear in response to loss of a volatile component). Mechanism descriptions are accompanied by experimental examples. Alternative methods to the direct imaging of OPBs are also presented.

In situ synchrotron X-ray scattering and fluorescence techniques were used to simultaneously observe the evolution of the strain and composition of a growing crystal surface in real time. Control of the X-ray incidence angle allows us to obtain high surface sensitivity. We studied metal organic chemical vapor deposition (MOCVD) of epitaxial PbZr x Ti 1-x O 3 (PZT) onto SrTiO 3 (001) substrates under various growth conditions. We observe a strong increase in Zr incorporation as strain relaxation occurs, consistent with the effect of compositional strain on the thermodynamic driving force for growth.

In situ synchrotron X-ray scattering was used to observe both the growth of PbTiO3 films by metal-organic chemical vapour deposition and the behaviour of the ferroelectric phase transition as a function of film thickness. The dependences of growth mode and deposition rate on gas flows and substrate temperature were determined by homoepitaxial growth studies on thick films (50 nm). These studies facilitated the growth of thin coherently strained PbTiO3 films on SrTiO3 (001) substrates, with thicknesses ranging from 2 to 42 nm. Experiments on the ferroelectric phase transition as a function of film thickness were carried out in these films under controlled mechanical and electrical boundary conditions.

Systems with a ferroelectric to paraelectric transition in the vicinity of room temperature are useful for devices. Adjusting the ferroelectric transition temperature (T(c)) is traditionally accomplished by chemical substitution-as in Ba(x)Sr(1-x)TiO(3), the material widely investigated for microwave devices in which the dielectric constant (epsilon(r)) at GHz frequencies is tuned by applying a quasi-static electric field. Heterogeneity associated with chemical substitution in such films, however, can broaden this phase transition by hundreds of degrees, which is detrimental to tunability and microwave device performance. An alternative way to adjust T(c) in ferroelectric films is strain. Here we show that epitaxial strain from a newly developed substrate can be harnessed to increase T(c) by hundreds of degrees and produce room-temperature ferroelectricity in strontium titanate, a material that is not normally ferroelectric at any temperature. This strain-induced enhancement in T(c) is the largest ever reported. Spatially resolved images of the local polarization state reveal a uniformity that far exceeds films tailored by chemical substitution. The high epsilon(r) at room temperature in these films (nearly 7,000 at 10 GHz) and its sharp dependence on electric field are promising for device applications.

Ferroelectric domain structures of (001)SrBi2Nb2O9 epitaxial films, investigated using both transmission electron microscopy and phase-field simulations, are reported. Experiment and numerical simulation both reveal that the domain structures consist of irregularly shaped domains with curved domain walls. It is shown that the elastic contribution to domain structures can be neglected in SrBi2Nb2O9 due to its small ferroelastic distortion, less than 0.0018%. Two-beam dark-field imaging using reflections unique to domains of each of the two 90° polarization axes reveal the domain structure. Phase-field simulation is based on the elastic and electrostatic solutions obtained for thin films under different mechanical and electric boundary conditions. The effects of ferroelastic distortion and dielectric constant on ferroelectric domains are systematically analyzed. It is demonstrated that electrostatic interactions which favor straight domain walls are not sufficient to overcome the domain wall energy which favors curved domains in SrBi2Nb2O9.

We have used in situ synchrotron x-ray scattering to investigate PbTiO3 films grown epitaxially on SrTiO3 (001) substrates. When the films are cooled below a thickness-dependent Curie temperature, the ferroelectric phase forms as 180° stripe domains with a well-defined period. With further cooling, the period changes fairly abruptly from a lower to a higher value, suggesting a transition between two stripe domain phases. The periods of both stripe phases are observed to depend on the square root of film thickness, in agreement with theory.

Thin films of Ba1−x Sr x Ti1+y O3+z (BST), were fabricated using both by RF-magnetron sputtering and MOCVD to demonstrate application to high frequency devices. Precise control of composition and microstructure is critical for the production of (Ba x Sr1−x )Ti1+y O3+z (BST) dielectric thin films with the large dependence of permittivity on electric field, low losses, and high electrical breakdown fields that are required for successful integration of BST into tunable high frequency devices. Here we review results on composition-microstructure-electrical property relationships of polycrystalline BST films produced by magnetron sputter deposition that are appropriate for microwave devices such as phase shifters. BST films with a multilayer structure were also developed with different Ti-elemental ratio in each layer to minimize losses and leakage current. Interfacial contamination from C and H species was studied and implications on electrical properties are highlighted. Finally, York's group at the University of California-Santa Barbara successfully integrated our BST films onto phase shifter arrays. The results show potential of BST films in such applications. Results from initial work on the integration of Cu-electrodes with BST films are also presented.

As part of a program to understand and control the structure of ferroelectric thin films grown by metal organic vapor phase epitaxy (MOVPE), we have used X-ray scattering to observe the surface structure of PbTiO 3 films during and following growth. Moderately high energy (24 keV) X-rays are used to penetrate the chamber walls for in situ measurements in the high-temperature, reactive MOVPE environment. Performing measurements in situ allows us to study the growth process in real time, to control the thickness of the films to sub-unit-cell accuracy, to observe the surface structure in equilibrium with the vapor, and to preserve film stoichiometry during high-temperature study by maintaining an overpressure of PbO. While the higher X-ray energy also permits a large volume of reciprocal space to be mapped, it presents challenges for surface scattering due to the small critical angle. Examples of results will be presented from studies of surface structure dynamics, crystal growth, and ferroelectric stripe domains in thin films.

Low dielectric loss and high electrical breakdown fields, in conjunction with an application-specific permittivity response, are simultaneous requirements for (Ba{sub x}Sr{sub 1-x})Ti{sub 1+y}O{sub 3+z} thin films. This has proved problematic, in that synthesis conditions which tend to reduce dielectric loss also tend to reduce zero-bias permittivity and electric-field tunability of the permittivity, thereby necessitating undesired compromises in overall performance for some applications. In order to address this problem of simultaneous optimization, we fabricated BST thin films with very low dielectric loss, Ti-rich BST layers ((Ba+Sr)/Ti=0.73) at the electrode/BST interfaces, in series with a primary, high tunability, high permittivity BST layer ((Ba+Sr)/Ti=0.9) in the center of this layered BST structure. Planar capacitors fabricated from the BST films exhibit low dielectric loss (tan {delta}=0.005) simultaneously with high (76%) tunability at room temperature and high breakdown fields ({approx}4 MV/cm), compared with capacitors with a single BST layer (Ba+Sr/Ti=0.9). Post annealing of the layered BST films at 800 C further improved dielectric loss down to 0.003, while keeping the high tunability and high breakdown field of the as-deposited films.

High permittivity (BaxSr1−x)Ti1+yO3+z(BST) thin films are being investigated for integration into charge storage dielectrics and electric-field tunable elements for high frequency devices. For the latter application, it is desirable to have BST capacitors with high tunability and low losses. Therefore, we investigated the use of multilayer BST thin films consisting of very low dielectric loss BST/electrode interfacial layers ((Ba+Sr)/Ti = 0.73) sandwiching a high tunability, high permittivity primary BST layer ((Ba+Sr)/Ti = 0.9). BST capacitors with multiple layers of controlled composition can be effectively produced insitu by magnetron sputter deposition, using a single stoichiometric target and controlling the layer composition by changing the total process gas (Ar+O 2.8 MV/cm).

We have investigated the structural and electrical characteristics of (BaxSr1−x)Ti1+yO3+z (BST) thin films synthesized at 650°C on Pt/SiO2/Si substrates using a large area, vertical metalorganic chemical vapor deposition (MOCVD) reactor equipped with a liquid delivery system. Films with a Ba/Sr ratio of 70/30 were studied, as determined using X-ray fluorescence spectroscopy (XRF) and Rutherford backscattering spectrometry (RBS). A substantial reduction of the dielectric loss was achieved when annealing the entire capacitor structure in air at 700°C. Dielectric tunability as high as 2.3:1 was measured for BST capacitors with the currently optimized processing conditions.

Epitaxial Pb(Mg1/3Nb2/3)O3 (PMN) and (l-x)(Pb(Mg1/3Nb2/3)O3)-x(PbTiO3) (PMN-PT) thin films have been deposited by metalorganic chemical vapor deposition at 700 – 780°C on (100) SrTiO3 and SrRuO3/SrTiO3 substrates. Room temperature values of 900 and 1.5%, were measured for the zero-bias permittivity and loss respectively, at 10 kHz for 220 nm thick pure PMN films. For PMN-PT films, the small-signal permittivity ranged from 1000 to 1500 depending on deposition conditions and Ti content; correspondingly low values for the zero-bias dielectric loss between 1 and 5% were determined for all samples. For PMN-PT with x of approximately 0.30–0.35, polarization hysteresis with Prμ18μC/cm2 was obtained. Initial piezoresponse results are discussed.

Polycrystalline Pb(ZrxTi1−x)O3 thin films with x = 0.6 and 1.0 were deposited at low temperatures (450–525 °C) on (111)Pt/Ti/SiO2/Si substrates by metalorganic chemical vapor deposition. The films were characterized by x-ray diffraction, electron microscopy, and electrical measurements. The texture of the films could be improved by using one of two template layers: PbTiO3 or TiO2. Electrical properties, including dielectric constants, loss tangents, polarization, coercive field, and breakdown field, were also examined. PbZrO3 films on Pt/Ti/SiO2/Si with a pseudocubic (110) orientation exhibited an electric-field-induced transformation from the antiferroelectric phase to the ferroelectric phase. The effect of varying processing conditions on the microstructure and electrical properties of the films is discussed.

Epitaxial, perovskite Pb(Mg1/3Nb2/3)O3–PbTiO3 films were grown by metalorganic chemical vapor deposition under various deposition conditions and characterized by x-ray diffraction and transmission electron microscopy. Pyrochlore free films were obtained under all deposition conditions used in this study. Magnesium-rich growth conditions lead to the formation of a Mg-rich impurity phase in the films, embedded as coherent lamellae parallel to the growth direction. Depending on the growth conditions, a wide variation in the stoichiometry and volume fraction of this impurity phase was found between samples, whereas morphology and crystal structure were found to be very similar.

In this paper, we investigate the role of grain boundaries in polycrystalline (Ba x Sr1−x )Ti1+y O3+z films, grown by metal organic vapor deposition, in the accommodation of nonstoichiometry, as well as their role in the strong composition dependence of the electric and dielectric behavior observed in these films. High-spatial resolution electron energy-loss spectroscopy is used for the analysis of composition and structural changes at grain boundaries, as a function of film composition. The existence of amorphous, titanium rich, TiO2-like phases at the grain boundaries of films with large amounts of excess Ti (y ≥ 0.08) may explain the non-monotonic resistance degradation behavior of the films as a function of Ti content. However, we show that a grain boundary phase model fails to explain the strong composition dependence of the dielectric behavior. Electron energy-loss spectra indicate a distortion of the Ti–O octahedra in the grain interiors in samples with increasing Ti excess. The decrease of the dielectric constant with increasing amounts of excess Ti is therefore more likely due to Ti accommodation in the grain interiors.

Ferroelectric SrBi2Ta2O9 (SBT) thin films on Pt/ZrO2/SiO2/Si were successfully prepared by using an alkanolamine-modified chemical solution deposition method. It was observed that alkanolamine provided stability to the SBT solution by retarding the hydrolysis and condensation rates. The crystallinity and the microstructure of the SBT thin films improved with increasing annealing temperature and were strongly correlated with the ferroelectric properties of the SBT thin films. The films annealed at 800 °C exhibited low leakage current density, low voltage saturation, high remanent polarization, and good fatigue characteristics at least up to 1010 switching cycles, indicating favorable behavior for memory applications.

We have investigated the dielectric response of a series of {100} fiber-textured (BaxSr1−x)Ti1+yO3+z samples deposited by liquid-source metalorganic chemical vapor deposition onto Pt/SiO2/Si, as a function of the two most commonly varied microstructural parameters: film thickness and Ti nonstoichiometry y. We find that the overall behavior of these samples is adequately described by mean-field, Landau–Ginzburg–Devonshire theory as for bulk ferroelectrics. However, we quantify the impact of three separable factors for these films that greatly alter the dielectric susceptibility as a function of temperature, compared to that found for bulk ceramic samples at the same Ba/Sr ratio of 70/30: (i) Ti nonstoichiometry; (ii) the apparent interface effect; and (iii) the plane equibiaxial stress state resulting from thermal expansion mismatch strains. When these factors are properly taken into consideration, we show that these fine grained thin films behave in a manner entirely consistent with expectations based on ...

The crystallinity and the microstructure of Sr0.8Bi2.3Ta2O9 (SBT) thin films improved with increasing annealing temperature, and strongly influenced the ferroelectric properties. In addition, the properties of SBT films, such as remanent polarization and leakage current density, are closely related to the film/electrode interface and surface roughness of the underlying electrode. SBT films on Pt/TiO2/SiO2/Si and Pt/ZrO2/SiO2/Si substrates exhibited high remanent polarization, low leakage current density, and low voltage saturation as compared to SBT films on Pt/Ti/SiO2/Si substrates. This is deduced to be related to differences in film orientation, electrode roughness, and out-diffusion of Ti onto the surface of the bottom electrode.

The ferroelectric and piezoelectric properties of 2000 {angstrom} thick chemical solution deposited Pb(Zr{sub x}Ti{sub 1{minus}x})O{sub 3} (PZT) thin films were investigated. Several Zr/Ti ratios were studied: 30/70, 50/50 and 65/35, which correspond to tetragonal, near-morphotropic, and rhombohedral symmetries. In all samples, a {l_brace}111{r_brace}-texture is predominant. Longitudinal piezoelectric coefficients and their dc field dependence were measured using the contact AFM method. The expected trend of a maximum piezoelectric coefficient at or near to the MPB was not observed. The composition dependence was small, with the maximum d{sub 33} occurring in the tetragonal material. To explain the results, crystallographic texture and film thickness effects are suggested. Using a modified phenomenological approach, derived electrostrictive coefficients, and experimental data, d{sub 33} values were calculated. Qualitative agreement was observed between the measured and calculated coefficients. Justifications of modifications to the calculations are discussed.

Mixed composition layered lead zirconate titanate (PZT) films sZr/Ti ratio = 30/70 + 65/35d with stoichiometric lead containing PZT thin layer at the film/electrode interface were successfully fabricated by a modified chemical solution deposition method. These modified PZT thin films are highly (111) textured, and have square-shaped P-E hysteresis loops with large remanent polarization and low coercive field, as well as low saturation voltage. In addition, these films show good fatigue and imprint behavior with Pt electrodes; the retained polarization of the modified film was above 50% after fatigue testing to 109 cycles, and the thermally induced voltage shifts (ΔV) were 0.51 V after heating at 150 °C for 4410 s, two times lower than for films without a stoichiometric thin layer.

We have investigated the effect of oxygen vacancies on imprint and fatigue behavior of the PLZT thin films. It is found that the compensation of oxygen vacancies with various dopant concentrations and electrode structures is an important process parameter in determining the tendency to imprint and fatigue. In the case of PLZT thin films, the voltage shifts related to imprint are attributed to the trapping of electrons at ionic defect sites such as oxygen vacancies near the film/electrode interface, the magnitude of polarization, and concentration of defect-dipole complexes involving oxygen vacancies such as V′Pb–V••o. The strong dependence of fatigue rate on electrode material for PLZT thin films is due to the effect of the ferroelectric/electrode interaction on the pinning and/or unpinning rate involving the accumulation of oxygen vacancies near the film/electrode interface during fatigue cycling. By using RuO2 as the top and/or bottom electrode instead of Pt, improved fatigue properties are obtained compared to Pt/PLZT/Pt capacitors. This is because a reduced accumulation of oxygen vacancies near the interface by the oxide electrode such as RuO2 may reduce the electronic charge trapping and, consequently, lead to less domain wall pinning.

We have investigated the effect of RuO2 (10, 30, 50 nm)/Pt layered hybrid bottom electrode structure and film composition on the leakage and fatigue properties of chemical solution derived Pb(ZrxTi1−x)O3 (PZT) thin films. It was observed that the use of high Ti content (Zr: Ti = 30: 70) films with control of excess PbO at the thin RuO2 (10 nm)/Pt bottom electrode surface reduced leakage current and showed good fatigue properties with high remanent polarization compared to the use of high Zr films (Zr: Ti = 50: 50) or thicker RuO2 (30, 50 nm)/Pt bottom electrodes. Typical P-E hysteresis behavior of PZT films was observed even at an applied voltage of 3 V, demonstrating greatly improved remanence and coercivity. Fatigue and breakdown characteristics of these modified PZT thin films (Zr: Ti = 30: 70) on RuO2 (10 nm)/Pt, measured at 5 V, showed stable behavior, and less than 15% fatigue degradation was observed up to 1010 cycles.

Recent developments in ferroelectric films have been made in terms of their application in nonvolatile memories and dynamic random access memories. One highlight is the report of a complete description of the temperature-dependent dielectric behavior of (Ba, Sr)TiO 3 films as a function of strain, composition, and thickness. For the first time, a direct link has been made between the thin film and bulk electrical properties.

The electrical properties and surface morphologies of (Ba, Sr)TiO3 thin films, with various bottom electrode structures, deposited by liquid delivery metal organic chemical vapor deposition were investigated. Ir and Ru films as a bottom electrode with varying deposition temperatures were prepared onto SiO2 and polySi substrate structures using ion beam sputtering technique. It is observed that electrical properties of BST films deposited by liquid delivery MOCVD was changed with the deposition temperatures of Ir and Ru as well as substrate structures. Furthermore, it is revealed that these variations in leakage current could be strongly related with the roughness of BST films.

We investigate the imprint phenomenon by poling ferroelectric PLZT capacitors into a known state and exposing the devices to elevated temperatures. It is found that the compensation of oxygen vacancies is a important process parameter in determining the tendency to imprint. In the case of PLZT thin films, the voltage shifts related to imprint failure are attributed to the trapping electrons at defect sites near film/electrode interface, the magnitude of polarization and concentration of defect-dipole complexes involving oxygen vacancies such as V″Pb - V″o. The thermally induced voltage shifts in PLZT thin films are dopant concentration dependent and decrease with increasing the La concentration of the films.

Possible domain patterns are developed for (001) oriented (pseudocubic indexing) epitaxial rhombohedral perovskite ferroelectric (FR) films. We assume that the films are grown above their Curie temperature (TC) in a cubic paraelectric (PC) state. The rhombohedral distortion consists of a “stretch” along one of the four 〈111〉 crystallographic directions of the cubic perovskite unit cell. Domain pattern formation is concurrent with the PC→FR transformation on cooling from the growth temperature. The domain patterns form to minimize elastic energy in the film, at the energetic expense of both forming domain boundaries and developing local stresses in the substrate. Eight possible domains may form, half of which are related by inversion, thus leading to four mechanically distinct variants. The possible domain walls are determined by mechanical and charge compatibility and follow closely from the analysis of Fousek and Janovec [J. Appl. Phys. 40, 135 (1969)]. Domain patterns may develop with either {100} or {1...

The coherency defect technique is developed for the domain pattern energetics in rhombohedral (001) epitaxial ferroelectric films. The coherency defects that are necessary to maintain the epitaxy during the ferroelectric phase transition are considered to be the only sources of elastic strains and stresses (and, correspondingly energy) in the film/substrate system. The coherency defects include: (i) a uniform distribution of edge dislocations which are responsible for the in-plane tension or compression and have Burgers vectors parallel to the interface; and two kinds of mesoscale defects: (ii) Somigliana screw dislocations which are responsible for in-plane shear; and (iii) wedge disclinations which are responsible for the out of plane rotations in neighboring domains. Using this approach, analytical expressions were found for the elastic energy in the film/substrate system for both the {101}-ri/rj and the {100}-ri/rj domain patterns. These two configurations differ by the orientation of domain walls, coherency defect content, and also the morphology of the free surface (flat versus puckered surfaces). Calculations are performed for screened mesoscale coherency defect configurations that represent a single embedded domain pattern and multidomain patterns. The following mesoscale defect configurations are used for these calculations: Somigliana dislocation dipoles, wedge disclination dipoles, Somigliana dislocation quadrupoles, and disclination quadrupoles. It is predicted that there is no critical thickness for domain pattern formation in rhombohedral ferroelectric epitaxial films. Agreement is shown between experimentally observed domain widths and theoretically predicted values.

The resistance degradation behavior of Ba0.7Sr0.3TiO3 (BST) and SrTiO3 (ST) thin films is compared to the degradation behavior of titanate single crystals and ceramics with respect to the dependence on parameters such as temperature, thickness of the sample, applied voltage, acceptor dopant concentration and electrode material. Different model considerations to explain the resistance degradation in titanate thin films are discussed.

The temperature- and field-dependent permittivities of fiber-textured Ba0.7Sr0.3TiO3 thin films grown by liquid-source metalorganic chemical vapor deposition were investigated as a function of film thickness. These films display a nonlinear dielectric response under conditions representative of those encountered in dynamic random access memories or other integrated capacitor applications. This behavior has the exact form expected for a classical nonlinear, nonhysteretic dielectric, as described in terms of a power series expansion of the free energy in the polarization as in the Landau–Ginzburg–Devonshire approach. Curie–Weiss-like behavior is exhibited above the bulk Curie point (∼300 K), although the ferroelectric phase transition appears frustrated. Small-signal capacitance measurements of films with different thicknesses (24–160 nm) indicate that only the first term in the power series expansion varies significantly with film thickness or temperature. Possible origins for this thickness dependence are...

(Ba,Sr)TiO3 (BST) thin films grown by chemical vapor deposition and with platinum (Pt) top and bottom electrodes have been characterized with respect to the leakage current as a function of temperature and applied voltage. The data can be interpreted via a thermionic emission model. The Schottky approximation accounts for superohmic behavior at higher fields, but the barrier lowering is stronger than expected from this theory. While the leakage mechanism is comparable to SrTiO3 thin films prepared by chemical solution deposition, the absolute values of the leakage current are significantly lower for the metalorganic chemical vapor deposition (MOCVD) prepared BST film. This is presumably due to a more homogeneous microstructure of the latter and may also be due to different electrode processing. The influence of the film thickness on the leakage in combination with additional findings is used to discuss the field distribution in the films under a dc voltage stress.

An important application of ferroelectric films is their incorporation into dynamic random-access memories (DRAMs) as the storage node capacitor dielectric. Dynamic random-access memories represent a large market that is experiencing strong growth, but they are particularly significant as the technology leader for semiconductor devices. As products move to higher and higher integration density, new developments are first introduced in DRAMs. The steady trend toward higher density has placed severe demands on the device designs, particularly with respect to “squeezing” the capacitor into the available space.

An approach for embedding high-permittivity dielectric thin films into glass epoxy laminate packages has been developed. Lead lanthanum zirconate titanate (Pb0.85La0.15(Zr0.52Ti0.48)0.96O3, PLZT) thin films were prepared using chemical solution deposition on nickel-coated copper foils that were 50 μm thick. Sputter-deposited nickel top electrodes completed the all-base-metal capacitor stack. After high-temperature nitrogen-gas crystallization anneals, the PLZT composition showed no signs of reduction, whereas the base-metal foils remained flexible. The capacitance density was 300–400 nF/cm2, and the loss tangent was 0.01–0.02 over a frequency range of 1–1000 kHz. These properties represent a potential improvement of 2–3 orders of magnitude over currently available embedded capacitor technologies for polymeric packages.

The mechanical properties of metal reinforced ceramics, especially Al/Al2O3 composites with interpenetrating networks, are described. Key parameters to tailor the characteristics of these materials are the ligament diameter and volume fraction of ductile reinforcement. Fracture strength and fracture toughness data are given as a function of both variables and are compared with the corresponding values for the porous preforms. A simple model accounts for the influence of metal volume and metal ligament diameter on the plateau toughness of the composites. The increase in fracture strength from the porous preform to the composite is found to be much larger than the gain which can be predicted from the increase in fracture toughness alone. A discussion of fracture strength in these composites therefore must include at least two issues, crack propagation through the matrix as well as crack initiation at metal filled pores.

We have used conventional and high-resolution transmission electron microscopy to investigate the microstruture of epitaxial, ferroelectric PbTiO3films grown by pulsed laser ablation on (001) MgO single crystals, and on MgO covered with epitaxial Pt or SrTiO3. Pronounced variations are found in the widths and lengths ofa-axis-oriented domains in these films, although the volume fraction ofa-axis-oriented material varies only weakly for the different types of samples. In addition, the films deposited onto Pt-coated MgO have a larger grain size than those deposited onto bare MgO or SrTiO3/MgO. Possible reasons for the variations in the distribution ofa-axis-oriented material in these samples include differences in the elastic properties and electrical conductivities of the different substrate combinations.

Using conventional and high resolution transmission electron microscopy, the dislocation structures in PbTiO3 thin films grown epitaxially on [001]-oriented MgO and SrTiO3 single crystals are studied. High resolution cross-sectional images of the films grown on MgO exhibit misfit dislocations with Burgers vectors of 1/2 〈010〉 and line directions of 〈100〉. The latter are identified by imaging the interface in two non-parallel zone axes. Plan-view studies of films grown on SrTiO3 reveal dislocations with Burgers vectors of 〈010〉 lying along 〈100〉 directions in the plane of the film. High resolution microscopy of cross-sectional samples shows dislocations in these films that have the additional half-plane on the substrate side of the film, opposite to what is required to accommodate the lattice misfit at room temperature. The mechanisms for dislocation formation and the role of the dislocations in stress relaxation with respect to the competing mechanism of 90° domain formation are discussed. Mit konventioneller und hochauflosender Transmissionselektronenmikroskopie werden Versetzungs-strukturen in PbTiO3-Filmen, die epitaktisch auf [001]-orientierten MgO- und SrTiO3-Einkristallen aufgewachsen wurden, untersucht. Hochauflosungsbilder von Querschnittsproben der Filme auf MgO zeigen Misfit-Versetzungen mit Burgers-Vektoren von 1/2 〈010〉 und Linienrichtungen von 〈100〉. Die letzteren werden durch eine Abbildung der Grenzflache in zwei nicht parallelen Zonenachsen bestimmt. Untersuchungen von Aufsichtsproben der Filme auf SrTiO3 zeigen Versetzungen mit Burgers-Vektoren von 〈010〉 entlang der 〈100〉 Richtungen der Filmebene. Hochauflosende Mikroskopie an Querschnitts-proben zeigt Versetzungen in diesen Filmen, bei denen sich die eingeschobene Halbebene auf der Substratseite des Films befindet, genau umgekehrt, wie es zum Ausgleich der Gitterfehlpassung bei Raumtemperatur notwendig ware. Die Mechanismen fur die Entstehung der Versetzungen und ihre Rolle beim Abbau von Spannungen unter Berucksichtigung des konkurrierenden Mechanismus, der Bildung von 90° Domanen, werden diskutiert.

Using transmission electron microscopy, we have compared the domain configurations in epitaxial, ferroelectric PbTiO 3 films grown on different substrates and to different film thicknesses. These configurations change considerably between the different samples. In addition, we have characterized the film/substrate interfaces by high-resolution transmission electron microscopy. It is proposed that the elastic properties of the substrate play a role in determining the domain configuration by influencing the accommodation of tilts of the film lattice.

Grazing-incidence small-angle x-ray scattering (GISAXS) and high-resolution transmission electron microscopy (HRTEM) were used to investigate phase separation in hafnium silicate films after rapid thermal annealing between 700 and 1000 °C. 4-nm-thick Hf–silicate films with 80 and 40 mol % HfO2, respectively, were prepared by metalorganic vapor deposition. Films of the two compositions showed distinctly different phase-separated microstructures, consistent with two limiting cases of microstructural evolution: nucleation/growth and spinodal decomposition. Films with 40 mol % HfO2 phase separated in the amorphous by spinodal decomposition and exhibited a characteristic wavelength in the plane of the film. Decomposition with a wavelength of ∼3 nm could be detected at 800 °C. At 1000 °C the films rapidly demixed with a wavelength of 5 nm. In contrast, films with 80 mol % HfO2 phase separated by nucleation and growth of crystallites, and showed a more random microstructure. The factors determining specific film...

The leakage and dielectric properties of a thickness series (90–480 nm) of {100} fiber-textured metalorganic chemical vapor deposited (Ba0.75Sr0.25)Ti1+yO3+z (BST) thin films on Pt/SiO2/Si were investigated. The permittivity demonstrated a suppressed temperature and electric field response that transitioned to a more bulk-like response with increasing thickness, consistent with earlier observations. At low fields the leakage currents showed a weak-field dependence and a monotonic increase with increasing temperature. In contrast, a positive temperature coefficient of resistance (PTCR) was observed in the leakage current behavior at high-field. The PTCR behavior was more pronounced for thicker BST films. The observed effect is contrasted with PTCR behavior in bulk BaTiO3 ceramics.

The volatility of bismuth and bismuth oxide species complicates the growth of phase-pure films of SrBi2Nb2O9 and SrBi2Ta2O9. Films that appear phase-pure by x-ray diffraction can have microstructural defects caused by transient bismuth nonstoichiometry which have a significant impact on properties. Such defects are resolved by transmission electron microscopy. Post-growth loss of bismuth from a slowly cooled SrBi2Ta2O9 film resulted in the generation of a high density of out-of-phase boundaries (OPBs), which are demonstrated to be ferroelectrically inactive. In another film, the difference in the rate of desorption of bismuth oxides from SrTiO3 versus that from SrBi2Nb2O9 led to bismuth enrichment at the film–substrate interface, and the formation of an epitaxial reaction layer in an otherwise stoichiometric SrBi2Nb2O9 film. This different-composition layer would be expected to alter the electrical properties of the film as a whole. These results help explain the scatter in electrical data reported for si...

(103) fiber-textured SrBi2Nb2O9 thin films have been grown on Pt-coated Si substrates using a SrRuO3 buffer layer. High-resolution transmission electron microscopy reveals that the fiber texture arises from the local epitaxial growth of (111) SrRuO3 grains on (111) Pt grains and in turn (103) SrBi2Nb2O9 grains on (111) SrRuO3 grains. The films exhibit remanent polarization values of 9 μC/cm2. The uniform grain orientation (fiber texture) should minimize grain-to-grain variations in the remanent polarization, which is important to continued scaling of ferroelectric memory device structures.

Barium strontium titanate thin films were deposited by sputtering on Pt/SiO2 structures using five different host substrates: magnesium oxide, strontium titanate, sapphire, silicon, and vycor glass. These substrates were chosen to provide a systematic change in thermal strain while maintaining the same film microstructure. All films have a weakly textured microstructure. Temperature dependent dielectric measurements from 100–500 K determined that decreasing thermal expansion coefficient of the host substrate (i.e., larger tensile thermal strain) reduced the film dielectric permittivity. The experimentally determined Curie–Weiss temperature decreased with increasing tensile thermal strain and the Curie–Weiss constant increased with tensile strain as predicted by Pertsev et al. [J. Appl. Phys. 85, 1698 (1999)].

We present in situ surface x-ray scattering measurements of PbTiO3 epitaxy by metal–organic chemical-vapor deposition. Oscillations in crystal truncation rod intensity corresponding to layer-by-layer growth are observed under a variety of growth conditions. At lower PbO overpressures, we observe a transition to step-flow growth and an increased rate of recovery after growth, indicating a higher surface mobility.

Microelectromechanical systems (MEMS) incorporating active piezoelectric layers offer integrated actuation, sensing, and transduction. The broad implementation of such active MEMS has long been constrained by the inability to integrate materials with giant piezoelectric response, such as Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PMN-PT). We synthesized high-quality PMN-PT epitaxial thin films on vicinal (001) Si wafers with the use of an epitaxial (001) SrTiO(3) template layer with superior piezoelectric coefficients (e(31,f) = -27 ± 3 coulombs per square meter) and figures of merit for piezoelectric energy-harvesting systems. We have incorporated these heterostructures into microcantilevers that are actuated with extremely low drive voltage due to thin-film piezoelectric properties that rival bulk PMN-PT single crystals. These epitaxial heterostructures exhibit very large electromechanical coupling for ultrasound medical imaging, microfluidic control, mechanical sensing, and energy harvesting.

We present a synchrotron x-ray study of the equilibrium polarization structure of ultrathin PbTiO(3) films on SrRuO(3) electrodes epitaxially grown on SrTiO(3) (001) substrates, as a function of temperature and the external oxygen partial pressure (pO(2)) controlling their surface charge compensation. We find that the ferroelectric Curie temperature (T(C)) varies with pO(2) and has a minimum at the intermediate pO(2), where the polarization below T(C) changes sign. The experiments are in qualitative agreement with a model based on Landau theory that takes into account the interaction of the phase transition with the electrochemical equilibria for charged surface species. The paraelectric phase is stabilized at intermediate pO(2) when the concentrations of surface species are insufficient to compensate either polar orientation.

The initial stages of deposition of a,b-axis-oriented YBa 2 Cu 3 O 7-δ onto LaAlO 3 substrates have been examined using transmission-electron microscopy. These films have their c axis parallel to the plane of the substrate throughout their thickness, including at the film-substrate interface: no initial layer with the c axis perpendicular to the plane of the substrate is observed. Nucleation of the c-parallel material is extremely dense, such that the triple perovskite layering along the c axis is sometimes disrupted, leading to structures containing two or four perovskite blocks instead of the usual three

We characterize the microscopic processes that take place during polarization reversal in the tetragonal phase of a monodomain order–disorder perovskite ferroelectric using molecular-dynamics simulation. Microscopically the polarization of each unit cell reorients from an [001] orientation to an [001] orientation through intermediate states with polarization parallel to [011] and [011]. For low electric field and low temperature, chains of polarization reverse in a spatially coherent manner, resulting in macroscopic intermediate states with orthorhombic symmetry. At high electric field and high temperature the process is completely incoherent and there is no well-defined macroscopic intermediate state.