Hsing‐Hung Hsieh

We report a model of the carrier transport and the subgap density of states in amorphous InGaZnO4 (a-IGZO) for device simulation of a-IGZO thin-film transistors (TFTs) operated in both the depletion mode and the enhancement mode. A simple model using a constant mobility and two-step subgap density of states reproduced well the characteristics of the a-IGZO TFTs. a-IGZO exhibits low densities of tail states and deep gap states, leading to small subthreshold swings and high mobilities.

Scaling behaviors of ZnO transparent thin-film transistors (TTFTs) have been studied by fabricating series of miniaturized ZnO TTFTs having various channel widths and lengths. Mobility of >8cm2∕Vs and on/off ratio of up to 107 are achieved with these TTFTs. Results show that these ZnO TTFTs retain rather well-behaved transistor characteristics down to the channel length of ∼5μm, rendering possible high-resolution applications. More apparent short-channel effects (e.g., lowering of threshold voltages, degradation of the subthreshold slope with the decrease of the channel length and the increase of the drain voltage, loss of hard saturation, etc.) are observed when the channel length is reduced below 5μm.

Oxide-semiconductor-based thin-film transistors (TFTs), particularly the amorphous ones, are becoming an important emerging technology. Since oxide semiconductors easily form polycrystalline phases, usually more complicated oxide mixtures are needed for growing amorphous phases. In this letter, we report that by simply reducing the thickness, ZnO can be intentionally grown into the amorphous phase. Furthermore, both top-gate and bottom-gate amorphous ZnO TFTs of micrometer scales were effectively implemented using fully lithographic and etching processes. Rather high field-effect mobilities of 25 and 4cm2∕Vs and on∕off current ratios of >107 and >106 were achieved for top-gate and bottom-gate configurations, respectively.

A long bothering issue in microcavity organic light-emitting devices (OLEDs) is the difficulty to simultaneously achieve enhanced cd/A efficiency, enhanced external quantum efficiency, enhanced color saturation, and stable colors with viewing angles in the same device design. In this work, we show that microcavity top-emitting OLEDs integrated with microlenses may provide a universal approach for simultaneously achieving all these desired nice characteristics. Furthermore, the pixel blurring often occurring in employment of microlenses to conventional bottom-emitting OLEDs is significantly suppressed by combination of top-emitting microcavity OLEDs and microlenses.