[en] In the field of phototonics there is an increasing demand for devices capable of storing and processing large quantities of optical information. Ferroelectric films, especially those based on (Pb,La) (Zr, Ti)O₃ solid solutions exhibit a combination of properties, such as large electrooptic coefficients, high photosensitivities, and nonvolatile memory that make them particularly attractive for these applications. Storage of optical images or data is based on the ability to modify the switching voltage for domain reorientation by illumination. Optical techniques for reading and processing stored information are based on either the quadratic electrooptic effect or on a photocurrent response. The mechanisms and limitations for image storage by photoactivated switching and for optical read-out and processing techniques will be discussed with respect to film composition and microstructure. In this paper the usage of ferroelectric films for optical storage disks, digital cameras, image comparators and spatial light modulators are discussed

[en] Ion irradiation was used to pattern a region of red-light emitting porous silicon by eliminating visible-light photoluminescence (PL). The PL peak wavelength is approximately 735 nm and shows little dependence on the excitation-light wavelength. The ratio of PL intensities for different excitation wavelengths was shown to be proportional to the ratio of the absorption coefficients. Below saturation, the integrated PL intensity increased linearly with excitation-light power density

[en] Spatially resolved resistivity measurements of current transport across individual grain boundaries have been made on superconducting YBa₂Cu_eO₇. These experiments were done by low-temperature scanning electron microscopy with a resolution of 1 to 2 micrometers, and they show directly the limitation of the critical current density caused by grain boundaries in YBa₂Cu₃O₇. Furthermore, complex spatial patterns of the current transport across grain boundaries were observed. These patterns reflect self-excited resonances of the grain boundaries and are closely correlated to the unexplained sub-gap structure in the current-voltage characteristics of polycrystalline YBa₂Cu₃O₇

[en] A detailed analysis of Pt/Ti, Pt/TiO₂, and Pt/ZrO₂ electrodes was carried out to develop a bottom electrode stack for sol-gel derived thin films capacitors. For the Pt/Ti stack, the choice of layer thickness and deposition temperature is found to affect adhesion to the SiO₂/Si substrate as well as the extent of hillock formation and Pt endash Ti interaction. By using elevated temperature deposition, Pt films close to 1 μm in thickness can be produced with relatively good adhesion and morphological stability using Ti adhesion layers. In addition, Pt films grown on ZrO₂ and TiO₂ adhesion layers exhibit little morphological change and no degradation in sheet resistance after annealing at 650 degree C. However, neither ZrO₂ nor TiO₂ are as effective as Ti metal in promoting Pt adhesion. Experiments aimed at establishing a correlation between hillock formation and capacitor yield revealed two important results. First, the behavior of Pt/Ti stacks during annealing in air is markedly different from their behavior during PZT film crystallization. Second, preannealing of the Pt/Ti in air prior to PZT film growth actually improves capacitor yield, even though hillock formation occurs during the preannealing treatment. Implications of these results regarding the role of hillocks in controlling capacitor yield are discussed. copyright 1997 Materials Research Society

[en] We find that the reduction of the switchable polarization in BaTiO₃ crystals via repeated polarization reversals (fatigue) is accompanied by the trapping of electronic charge and atomic scale distortions in the perovskite oxygen octahedron. The distortions are proposed to involve oxygen vacancies. copyright 1995 American Institute of Physics

[en] The authors report results for both magnetic and transport measurements on thin epitaxial films of YBa₂Cu₃O_7-chi which show critical current densities of 10⁷ amps/cm² at 4.2Κ. They have well formed symmetrical hysteresis loops, flux trapping effects at low fields and linear susceptibilities at low fields. Magnetic and transport critical currents are in good agreement at low temperatures. The above properties ar attributed to strong pinning from point defects which are suggested to be more numerous in films than in bulk single crystals

[en] The results of light-scattering measurements for a series of Pb(Zr,Ti)O₃ thin films prepared by a sol-gel method are presented and analyzed. The films differed due to the addition of different concentrations of acetylacetone to the precursor solution immediately prior to film fabrication. Visual inspection of the films indicated improvements in optical quality with the addition of acetylacetone. To quantify these improvements, two types of light-scattering measurements were performed: angularly resolved light scattering and spectrally resolved light scattering. Surprisingly, only slight differences between the films were observed using angularly resolved light scattering at 633 nm. In contrast, the spectrally resolved scattering revealed large differences between the films, with the films prepared using the largest concentrations of acetylacetone exhibiting the lowest scattering. The apparent contradiction between these findings is resolved using a theoretical model for light scattering due to fluctuations in the dielectric constant occurring within the volume of the thin film and by noting that slight thickness differences exist between the films in the series. Analysis of the light scattering from the best sample yields estimates for the amplitude (ξ₀ = 0.08) and the characteristic size (τ₀ = 110 nm) of the dielectric constant fluctuations. These estimates are consistent with the variations of the dielectric constant expected due to the birefringent, polycrystalline nature of these films

[en] It is shown that SrBi₂Ta₂O₉ (SBT) thin films can be made to exhibit significant polarization fatigue by electric-field cycling under broad-band, optical illumination. Photoinduced fatigue is also observed for Pb(Zr,Ti)O₃ (PZT) thin-film capacitors with (La,Sr)CoO₃ (LSCO) electrodes. These results demonstrate that both the Pt/SBT/Pt and the LSCO/PZT/LSCO systems are susceptible to fatigue effects, which are attributed primarily to pinning of domain walls due to charge trapping. Capacitors that have been fatigued under illumination can be fully rejuvinated by applying a dc saturating bias with light or by electric-field cycling without light, which indicates an intrinsic, field-assisted recovery mechanism. We suggest that fatigue is essentially a competition between domain wall pinning and unpinning and that domain pinning is not necessarily absent in these nominally fatigue-free systems, but rather these systems are ones in which unpinning occurs at least as rapidly as any pinning. In both cases, the extent of photoinduced fatigue decreases with increased cycling voltage, indicating the relative importance of field-assisted unpinning. Finally, the observation of photoinduced fatigue implies that increased injection rates, potentially due to oxygen vacancy accumulation, may account for the electrode dependence on fatigue in PZT thin films

[en] It is shown that voltage shifts in the hysteresis response of SrBi₂Ta₂O₉ (SBT) thin-film capacitors can be induced using both thermal and optical methods. These voltage shifts are important since they can lead to imprint failure in ferroelectric memory devices. It is suggested that the voltage shifts in the hysteresis curve of SBT are caused by trapping of electronic charge carriers near the film/electrode interfaces, as has been previously reported for the Pb(Zr,Ti)O₃ (PZT) system. In addition, a direct correlation is established between the magnitude and sign of remanent polarization (P_r) and the thermally induced voltage shifts (V_i), where V_i=αP_r+β. It is also found that, unlike the PZT system, the thermally induced voltage shifts in SBT are smaller than those optically induced. One possible implication of this result is that the contribution of defect endash dipole complexes to the voltage shifts in SBT is negligible. We suggest that the smaller contribution of defect-dipole complexes to the voltage shifts in SBT may be related to a smaller oxygen vacancy concentration in the perovskite sublattice of SBT as compared to that of PZT. copyright 1996 American Institute of Physics

[en] Pb(Zr,Ti)O₃ and (Pb,La)(Zr,Ti)O₃ thin films and bulk ceramics are shown to exhibit two distinct, but related types of photoinduced changes in their hysteresis behavior: (1) a photoinduced suppression of the switchable polarization and (2) a photoinduced voltage shift. Both effects give rise to stable and reproducible hysteresis changes and, thus, either could be the basis of an optical memory. Both phenomena can be explained by trapping of photogenerated charge at domain boundaries to minimize internal depolarizing fields. The space-charge field that causes the voltage-shift effect is primarily due to the migration and subsequent trapping of electrons. However, the thickness dependence of the voltage shift implies that the trapped charge is not confined to the interface. The voltage-shift kinetics exhibit a stretched-exponential dependence, whereas the polarization-suppression effect follows an exponential time dependence. However, both effects exhibit similar relaxation times. In addition, the relaxation time for the voltage-shift effect decreases with increasing light intensity according to a power-law relationship, τ∝I^-n, where 0.67< n<0.75