Ferroelectric thin films such as barium strontium titanate (BST) and lead zirconate titanate (PZT) are potential materials for high-density dynamic/ferroelectric random-access memory applications. However, the properties of BST and PZT thin films are observed to be significantly inferior to their bulk counterparts. In addition, ferroelectric PZT films, when configured with metal electrodes, generally experience loss of switchable polarization (fatigue) under repetitive electrical cycling. We have reported previously that an interfacial defect layer was observed in BST/Pt interfaces. In this article, we discussed the possible origin of the interfacial defect layer and the effect it has on the thickness-dependent properties. We further suggested that fatigue in ferroelectrics could be explained by a field screening mechanism in which only a small fraction of the applied voltage is seen by the film bulk due to the screening effect of the interfacial layers.
The method of solvent-enhanced dye diffusion for patterning full-color (red, green, and blue) polymer light-emitting diode displays was investigated in detail. After local dry transfer of dye onto a device polymer film, the dye remains on the surface of the polymer layer and must be diffused into the polymer for efficient emission. Exposure of the polymer to solvent vapor at room temperature increases the dye-diffusion coefficient by many orders of magnitude, allowing rapid diffusion of the dye into the film without a long, high-temperature anneal that can degrade the polymer. The increase in diffusion is due to absorption of the solvent vapor into the polymer film, which increases the polymer thickness and decreases its effective glass transition temperature T g,eff. Measurements of the polymer in solvent vapor indicate that its thickness varies roughly linearly with pressure and inversely with temperature, with thickness increases as large as 15% often observed. A model based on Flory-Huggins theory is used to describe these results. The diffusion of the dye into the polymer was evaluated by photoluminescence and secondary-ion mass spectroscopy. This dye-diffusion increase is largest for high solvent-vapor partial pressures and, most surprisingly, is larger at lower temperatures than at higher temperatures. This anomalous temperature dependence is due to the increased solvent-vapor absorption and consequent reduction in the effective glass-transition temperature at lower temperatures.
Abstract— A transfer‐printing method for the patterning of thin polymer layers is described. A hard stamp with a raised feature is brought into contact with a spin‐coated organic film under elevated pressure and temperature to break the films. The patterned film is then transfer printed onto the devices. This method is used to print red/green/blue subpixel arrays with a pattern size as small as 12 μm at a resolution of 530 ppi to demonstrate its ability for full‐color organic light‐emitting‐display fabrication. Devices with printed organic layers have similar performance to spin‐coated controls under optimized printing temperature and pressure settings. The critical physical parameters include a soft intermediate plate for the sharp breaking of edge patterns, control of surface energies, and printing at moderate temperature and pressure to achieve intimate contact between the printed layer and the underlying substrate.
We report on the performance of a planetary multi-wafer MOCVD reactor which handles 5 six inch wafers simultaneously. The reactor is combined with a liquid delivery system which mixes the liquid precursors from three different sources: 0.35 molar solutions of Ba(thd)2 and Sr(thd)2 and a 0.4 molar solution of Ti(O-i-Pr)2(thd)2. The microstructure and the film stress were investigated by X-ray diffraction and the composition of the films was determined by X-ray fluorescence analysis. As a direct consequence of the reactor design we obtain a high uniformity of the films over 6 inch wafers, as well as high efficiencies for the precursor incorporation. Film growth is discussed within a wide parameter field and the finally achieved electrical properties, e.g., permittivity, loss tangent, leakage current, are discussed in relation to the microstructural properties.
Various bismuth-based pyrochlore films were deposited on copper clad laminate substrates at temperatures below 150 °C by pulsed laser deposition for embedded capacitor applications. The films showed smooth and dense morphologies during deposition at room temperature. Bi2Mg2/3Nb4/3O7 (BMN) pyrochlore films showed the most stable dielectric properties and leakage current behaviors as a function of film thickness and deposition temperature. The capacitance density and breakdown field of 150-nm-thick-BMN films deposited at 150 °C were approximately 325 nF/cm2 and 410 kV/cm, respectively. The BMN films showed a dielectric constant of 55, a dielectric loss of 1.6% at 100 kHz, and a leakage current density of 1×10-8 A/cm2 at an applied field of 250 kV/cm. Metal/insulator/metal (MIM) capacitors including various bismuth-based pyrochlore films are expected to be promising candidates for printed circuit board (PCB)-embedded capacitors.
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