Highly reliable a‐IGZO TFTs on a plastic substrate for flexible AMOLED displays

We have successfully reduced threshold voltage shifts of amorphous In–Ga–Zn–O thin‐film transistors (a‐IGZO TFTs) on transparent polyimide films against bias‐temperature stress below 100 mV, which is equivalent to those on glass substrates. This high reliability was achieved by dense IGZO thin films and annealing temperature below 300 °C. We have reduced bulk defects of IGZO thin films and interface defects between gate insulator and IGZO thin film by optimizing deposition conditions of IGZO thin films and annealing conditions. Furthermore, a 3.0‐in. flexible active‐matrix organic light‐emitting diode was demonstrated with the highly reliable a‐IGZO TFT backplane on polyimide film. The polyimide film coating process is compatible with mass‐production lines. We believe that flexible organic light‐emitting diode displays can be mass produced using a‐IGZO TFT backplane on polyimide films.     

Production of uniform droplets using membrane, microchannel and microfluidic emulsification devices

This review provides an overview of major microengineering emulsification techniques for production of monodispersed droplets. The main emphasis has been put on membrane emulsification using Shirasu Porous Glass and microsieve membrane, microchannel emulsification using grooved-type and straight-through microchannel plates, microfluidic junctions and flow focusing microfluidic devices. Microfabrication methods for production of planar and 3D poly(dimethylsiloxane) devices, glass capillary microfluidic devices and single-crystal silicon microchannel array devices have been described including soft lithography, glass capillary pulling and microforging, hot embossing, anisotropic wet etching and deep reactive ion etching. In addition, fabrication methods for SPG and microseive membranes have been outlined, such as spinodal decomposition, reactive ion etching and ultraviolet LIGA (Lithography, Electroplating, and Moulding) process. The most widespread application of micromachined emulsification devices is in the synthesis of monodispersed particles and vesicles, such as polymeric particles, microgels, solid lipid particles, Janus particles, and functional vesicles (liposomes, polymersomes and colloidosomes). Glass capillary microfluidic devices are very suitable for production of core/shell drops of controllable shell thickness and multiple emulsions containing a controlled number of inner droplets and/or inner droplets of two or more distinct phases. Microchannel emulsification is a very promising technique for production of monodispersed droplets with droplet throughputs of up to 100?l?h^?1.     

Modification of mesophase pitch by blending Part 2 Modification of mesophase pitch fibre precursor with thermoresisting polyphenyleneoxide (PPO)

Polyphenyleneoxide was blended in amounts of 5 or 10 wt% into petroleum-derived mesophase pitch to reinforce the pitch fibre before the oxidative stabilization to achieve better handling properties. Although polyphenyleneoxide was fusible but hardly soluble in the mesophase pitch even at a spinning temperature of 350° C, blended pitch could be smoothly spun into pitch fibre 10m diameter, as could the parent pitch. Fibrous polyphenyleneoxide of less than 1m diameter was homogeneously dispersed in the pitch fibre, being arranged along the fibre axis. Such fibrous polyp henyleneoxide reinforced the pitch fibre considerably. The fibrous substances at the centre of the fibre disappeared in the carbonized fibre at 1300° C after oxidation at 250° C, although some short ones were observed in the skin region of the fibre, suggesting that polyphenyleneoxide was co-carbonized to be assimilated with mesophase pitch at the centre of the fibre, where the effects of oxidation may be rather limited. The oxidation reactivity and its mechanical strength after carbonization were slightly lower in comparison with those of the parent mesophase pitch.     

Effect of Composition on the Oxygen Tracer Diffusion in Transparent Yttrium Aluminium Garnet (YAG) Ceramics

The grain boundary structure and oxygen tracer diffusion in transparent yttrium aluminum garnet (YAG) ceramics varying from 2% excess of Y₂O₃ to 0.5% excess of Al₂O₃ were studied. The characterization of the specimens is as follows: (i) For the Y₂O₃-excess specimen, a second phase (yttrium aluminum perovskite: YAP) containing silicon in the grain boundary was found, (ii) For the Al₂O₃-excess specimen, both aluminum-rich particles (alumina) and a silicon-rich segregant layer were observed in the grain boundary. The volume diffusion of the oxygen tracer is little influenced by the excess composition. In contrast, the grain boundary diffusion of the oxygen tracer is suppressed in the Y₂O₃-excess specimens, compared to Al₂O₃-excess specimens. These differences are thought to result from the chemical reaction between the second phase and the intergranular liquid phase during the sintering.     

Carbonization of coals to produce anisotropic cokes. 1. Modifying activities of some additives in the co-carbonization of low-rank coals

Using low-rank coals, the modifying activities of some petroleum, coal tar and aromatic hydrocarbon additives have been examined to find procedures for their utilization in the preparation of blast furnace coke. Petroleum pitch, especially after hydrogenation, exhibited excellent modifying activity even with non-fusible coals. In contrast, the activity of coal tar was very limited with such coals. The napththenic component, revealed by n.m.r. of the additives, appears to be important in the co-carbonization by inducing fusibility and anisotropic development in such coals. Co-carbonization to recover the dehydrogenated additives was attempted. However, there was no development of the anisotropy in the resultant coke by dissolution of the coal particles although the coal particles were firmly fixed in the matrix. Acid-refluxing treatment of non-fusible coals was found to enhance their modification susceptibility, indicating that some of the acid-soluble mineral matter is important in the thermal depolymerization or fusion process of the coal.     

Preparation and performance of poly(vinyl butyral) membrane for ultrafiltration

Ultrafiltration membrane was prepared from poly(vinyl butyral). The effects of membrane thickness, polymer concentration, evaporation time, and evaporation temperature, etc., on the performance of the resulting membranes have been studied. Dimethylacetamide was used as a casting solvent. The membrane formed by casting the polymer from a 15 wt % solution and evaporation at 25°C for 30 s had a flux value of 250 cm³ / cm² h (4.8 kg/cm², 26°C) at 92.9% rejection level for dextran sodium sulfate (average mol. wt. 550,000) separation. © 1993 John Wiley & Sons, Inc.     

Synthesis of poly(α-thiophenediyl)benzylidene with high molecular weight and its thermal stability

Summary The synthesis of poly(-thiophenediyl)benzylidene (PTB) with high molecular weight is described. Number-average degrees of polymerization reached about 74. The characterizations of the polymer was investigated by ¹H-NMR, ¹³C-NMR, IR, and UV-VIS spectra. The polymer with well-defined structure and high molecular weight was obtained by polymerization at low temperature and in polar solvent. This polymer was thermally stable and a thermal decomposition took place at 391°C under nitrogen and at 370°C under air. The glass transformation temperature was 117°C and this PTB was nonfusible.     

Radiation grafting of α,β,β-trifluoroethylenesulfonyl fluoride onto low-density polyethylene film by simultaneous irradiation method. I. Kinetic study of simultaneous-irradiation grafting

α,β,β-Trifluoroethylenesulfonyl fluoride (TFESF) was grafted onto polyethylene (PE) film by a simultaneous-irradiation method. The influences of the grafting conditions were analyzed kinetically. The dependencies of the grafting rate on the dose rates and monomer concentrations ranging from 10 to 75% were found to be of 1 and 0 order, respectively. The overall activation energy for the graft polymerization was 2.05 × 10⁴ J/mol. The grafting rate was found to be independent of the film thicknesses ranging from 25 to 100 μm.     

Solubility of Si3N4 in Liquid SiO2

The nitrogen solubility in the SiO₂-rich liquid in the metastable binary SiO₂-Si₃N₄ system has been determined by analytical TEM to be 1%–4% of N/(O + N) at 1973–2223 K. Analysis of the near edge structure of the electron energy loss peak indicates that nitrogen is incorporated into the silicate network rather than being present as molecular N₂. A regular solution model with a positive enthalpy of mixing for the liquid was used to match the data for the metastable solubility of N in the presence of crystalline Si₃N₄ and to adjust the computed phase diagram. The solubility of Si₃N₄ in fused SiO₂ is far less than reported in liquid silicates also containing Al, Mg, and/or Y. Apparently, these cations act as modifiers that break anion bridges in the silicate network and, thereby, allow further incorporation of Si₃N₄ without prohibitive amounts of network cross-linking. Finally, indications emerged regarding the diffuse nature of the Si₃N₄-SiO₂ interface that leads to amorphous regions of higher N content.     

High-Temperature Fracture Mechanism of Low-Ca-Doped Silicon Nitride

High-purity Si₃N₄ (with 2.5 wt% glassy SiO₂) doped with 0 to 450 at.ppm of Ca was prepared as a model system to investigate the effects of grain-boundary segregants on fracture phenomenology at 1400°C. Subcritical crack-growth (SCG) resistance as well as creep resistance was degraded significantly by the presence of a small amount of Ca. The internal friction of the doped materials exhibited the superposition of a grain-boundary relaxation peak and a high-temperature background, and the apparent viscosity of the grain-boundary film was determined from the peak. Based on these experimental data, the fracture mechanism at 1400°C was divided into three regions: "brittle," SCG, and creep failure as a function of both external strain rate and Ca concentration, C _Ca. From the investigation of the C _Ca dependence of the critical strain rate for the transition from "brittle" to SCG fractures, the SCG phenomenon is suggested to be triggered by small-scale, grain-boundary sliding. The C _Ca dependence of "steady-state" creep rate was far from the theoretical dependence of diffusional creep via a solution-precipitation mechanism. The discrepancy was interpreted to be due to the presence of an impurity-insensitive creep component. This component may correspond to the lowest limit of the tensile creep rate in Si₃N₄ polycrystalline materials containing intergranular glassy-SiO₂ film.