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We have fabricated 6.5 in. flexible full-color top-emission active matrix organic light-emitting diode display on a polyimide (PI) substrate driven amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs). The a-IGZO TFTs exhibited field-effect mobility (μFE) of 15.1 cm2/V s, subthreshold slope of 0.25 V/dec, threshold voltage (VTH) of 0.9 V. The electrical characteristics of TFTs on PI substrate, including a bias-stress instability after 1 h long gate bias at 15 V, were indistinguishable from those on glass substrate and showed high degree of spatial uniformity. TFT samples on 10 μm thick PI substrate withstood bending down to R=3 mm under tension and compression without any performance degradation.

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Droughts are destructive climatic extreme events, which may cause significant damages both in natural environments and human lives. Drought forecasting plays an important role in the control and management of water resources systems. In this study, a conjunction model is presented to forecast droughts. The proposed conjunction model is based on dyadic wavelet transforms and neural networks. Neural networks have shown great ability in modeling and forecasting nonlinear and nonstationary time series in a water resources engineering, and wavelet transforms provide useful decompositions of an original time series. The wavelettransformed data aids in improving the model performance by capturing helpful information on various resolution levels. Neural networks were used to forecast decomposed sub-signals in various resolution levels and reconstruct forecasted sub-signals. The performance of the conjunction model was measured using various forecast skill criteria. The model was applied to forecast droughts in the Conchos River Basin in Mexico, which is the most important tributary of the Lower Rio Grande/Bravo. The results indicate that the conjunction model significantly improves the ability of neural networks for forecasting the indexed regional drought.

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Organometal halide perovskites have attracted widespread attention as the most favorable prospective material for photovoltaic technology because of their high photoinduced charge separation and carrier transport performance. However, the microstructural aspects within the organometal halide perovskite are still unknown, even though it belongs to a crystal system. Here direct observation of the microstructure of the thin film organometal halide perovskite using transmission electron microscopy is reported. Unlike previous reports claiming each phase of the organometal halide perovskite solely exists at a given temperature range, it is identified that the tetragonal and cubic phases coexist at room temperature, and it is confirmed that superlattices composed of a mixture of tetragonal and cubic phases are self-organized without a compositional change. The organometal halide perovskite self-adjusts the configuration of phases and automatically organizes a buffer layer at boundaries by introducing a superlattice. This report shows the fundamental crystallographic information for the organometal halide perovskite and demonstrates new possibilities as promising materials for various applications.

An active matrix-type stretchable display is realized by overlay-aligned transfer of inorganic light-emitting diode (LED) and single-crystal Si thin film transistor (TFT) with roll processes. The roll-based transfer enables integration of heterogeneous thin film devices on a rubber substrate while preserving excellent electrical and optical properties of these devices, comparable to their bulk properties. The electron mobility of the integrated Si-TFT is over 700 cm 2 V −1 s −1 , and this is attributed to the good interface between the Si channel and the thermally grown SiO 2 insulator. The light emission properties of the LED are of wafer quality. The resulting display stably operates under tensile strains up to 40%, over 200 cycles, demonstrating the potential of stretchable displays based on inorganic materials.Figure 7. Electrical and mechanical properties of Si-TFT, μ-LED, and integrated pixel device stretched by 0%, 20%, 30%, and 40%. a) Transfer plots and I-V (inset) characteristics of the transistor. b) I-V characteristics of the μ-LED. c) Plot of unit pixel current versus data voltage. Here, V Data sweeps from −1 to 9 V and the PDMS substrate is stretched up to 40%. d) Normalized on/off current values of the unit pixel at the initial state, after stretching, after recovery, and after repeated stretching-recovery.Figure 6. Optical images of a) experimental set-up for mechanical stretching test during AM addressing operation, followed by the insulation wiring process; b) a stretchable AM-LED display, showing uniform emission characteristics under uniaxial strain (top 0%, bottom 40%; white lines indicate the horizontal direction); c) magnified islands and bridges under the conditions of (b). d) Strain distribution on the stretchable AM-LED display, simulated by FEM. Most of the strain occurs on the serpentine-shaped bridge region; the strain on the island region is negligible.

We investigated the threshold voltage (Vth) instability for various gate dielectrics (SiNx and SiOx) in amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors (TFTs). The a-IGZO TFTs with SiNx 150 °C exhibited reasonable electrical performance (field-effect mobility of 8.1 cm2/V s and Ion/off ratio of >108) but showed huge Vth shift under positive gate bias. The TFTs with SiOx dielectrics exhibit smaller Vth instability than those of SiNx dielectrics. This behavior can be explained by using simple charge trapping into the gate insulators and the difference of Vth instability on various dielectrics may be originated from the hydrogen contents, providing high density of charge traps in gate dielectrics.