Threshold voltage shifts of a-IGZO TFTs on plastics against biastemperature stress were successfully reduced below 0.03 V, equivalent to those on glass substrates. We have developed an 11.7inch qHD (960×RGB×540) flexible bottom-emission active-matrix organic light-emitting diode (AMOLED) driven by a-IGZO TFT backplane fabricated on a transparent polyimide film.

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.

Characteristics have been investigated for both KrF excimer-laser light and KrF excimer-laser crystallization of Si thin films. The results were applied to design an optical system for growing densely packed and large grains. A high-resolution beam profiler confirmed that the laser light intensity distribution on the sample surface had a nearly ideal triangular form with a maximum-to-minimum intensity ratio of approximately 2, as designed. This distribution could grow 5-mm-long grains with a packing efficiency close to 100% by a single laser light pulse.

Phase-modulated excimer laser annealing ͑ELA͒ is an advanced excimer-laser crystallization method characterized by the intensity modulation of irradiated light by a phase modulator. In this method, a temperature gradient is formed in melted Si and large crystal grains are laterally grown at predetermined positions. In order to form grains with a high packing efficiency, a periodic "V-shaped" form of the light intensity distribution is desired. In the present study, a novel duty phase modulator is developed for projectiontype PMELA. The light intensity distribution on the sample surface can be freely controlled and its design method is simple. We confirmed that a V-shaped light intensity distribution could be achieved by preparing a prototype duty phase modulator. In addition, crystallization was carried out with this duty phase modulator and 5-m-long crystal grains with a high packing efficiency were successfully grown.Excimer laser crystallization ͑ELC͒ is a key technology for polycrystalline Si thin-film transistors ͑poly-Si TFTs͒ designed for system-on-glass devices and has been the subject of numerous studies. Phase-modulated excimer laser annealing ͑PMELA͒, which we have been investigating, is an advanced ELC method featuring the intensity modulation of irradiated light on a-Si using a phase modulator ͑Fig. 1͒. In this method, a temperature gradient is formed in melted Si and large crystal grains grow laterally at predetermined positions. In this way, a TFT channel section can be prepared from a single-crystal grain. TFTs of higher performance can be prepared from these large crystal grains than from conventional poly-Si.In order to form a whole circuit, it is necessary to grow large crystal grains with a high packing efficiency. For this purpose, the distribution of the light intensity is determined based on the following characteristics of lateral growth.1. Lateral growth starts at a certain "lateral growth starting intensity". At a lower light intensity, Si does not melt or it remains in the form of fine grains.2. Lateral growth takes place along the direction of the temperature gradient, namely, the direction of the light intensity gradient. If this gradient is small, the lateral growth will stop halfway.Based on these characteristics, we have identified the optimum distribution to have a periodic "V-shaped" form to grow crystal grains with a high packing efficiency. As shown in Fig. 2, crystal nuclei are generated at the bottom of the V-shape irradiating light intensity distribution. Subsequently, lateral growth can take place along the gradient of the V-shape to peak intensity points. In this way, it is possible to grow large crystal grains with a high packing efficiency. It is important that the light intensity at the bottom of the V-shape is exactly the lateral growth starting intensity. If the intensity at the bottom of the V-shape is too low, large grains cannot be formed in those regions. If the intensity at the bottom of the V-shape is too high, random nucleation, resulting in small grains, takes...

A conventional phase modulator having only “holes” (or “bumps”) on a quartz plate has been found to have insufficient depth-of-focus (DOF) characteristics. This poor DOF can be attributed to the phase advancement (or retardation) of the zeroth-order diffracted light wave. This phase effect has been applied to developing two types of modulator: one with a sufficiently large DOF, and the other, a single-plate phase modulator capable of producing a two-dimensional light intensity profile suitable for growing arrays of large grains. It was confirmed experimentally that this single-plate modulator could grow arrays of large grains 5 µm in pitch.