Yujiro Hara

4.1: Low-Temperature-Processed IGZO TFTs for Flexible AMOLED with Integrated Gate Driver Circuits

We have reduced threshold voltage shift of IGZO TFTs processed at 200°C under bias-temperature stress of Vg = 20 V at 70°C for 2000 s to 0.22 V by optimizing IGZO deposition and annealing conditions. A flexible AMOLED display with integrated gate driver circuits has been demonstrated.

Preparation of Pb(Zr, Ti)O3 Thin Films on Glass Substrates.

Lead-zirconate-titanate (PZT) thin films were prepared on non-alkaline glass substrates widely used in liquid crystal display (LCD) devices, by plasma-assisted magnetron RF sputtering with an immersed coil. After preparation of the PZT thin film, the glass was available for use in LCD device processing. No mutual diffusion of the elements was recognized between the glass substrate and the bottom electrode. The PZT layer had a dense film structure with rectangular and columnar grains, and only its perovskite phase was crystalline. PZT thin films on a glass substrate had leakage current densities of about 10-8 A/cm2, acceptable hysteresis loop shapes with the remanent polarization (Pr) of 45 µC/cm2 and the coercive field (Ec) of 90 kV/cm. Ferroelectric properties on a glass substrate almost conform with those on a Si-based substrate.

Equivalent Circuit Model for Thresholdless Antiferroelectric Liquid Crystal Displays

For high quality displays, analog responding liquid crystals with spontaneous polarization need to be coupled with active matrix driving schemes. Our goal is to investigate the possibilities for optimizing liquid crystal materials, thin film transistors, and driving schemes. In this paper, the electrooptical properties of thresholdless antiferroelectric (TLAF) liquid crystal displays (LCDs), which are analog responding, are modeled using an electric circuit which can be applied to conventional simulators. A novel procedure for deducing the circuit parameters on the basis of the experimental results is discussed. It was found that the voltage-dependent capacitance due to the induced spontaneous polarization is important for describing the static and dynamic behavior at different applied voltages. It is shown that our equivalent circuit model reproduces the pixel voltage as well as the transmittance of active-addressed TLAF-LCDs.

A 15‐in. XGA thresholdless antiferroelectric LCD addressed by TFTs and using the quasi‐dc driving method

— A 15-in. TFT-LCD with XGA resolution using thresholdless antiferroelectric liquid crystal (TLAF) has been developed. TLAF materials show V-shaped switching and enable display of analog gray scale, wide viewing angle, and fast response. However, in the case that high-resolution TFT-LCDs using materials with large spontaneous polarization such as TLAF were driven by the conventional method, alternating current (ac) driving, the obtained contrast ratio was limited because of a sharp decline of holding voltage due to the growth of a depolarization field. In order to enhance the contrast ratio, a novel driving method referred to as quasi-dc driving was proposed. In the quasi-dc driving, the polarity of the applied voltage to liquid crystals inverts at certain intervals of several seconds. Moreover, the applied voltage and the charging time at the time of polarity inversion are increased more than the intended signals. By this method, the 15-in. TFT-LCD using TLAF with high contrast ratio (more than 100:1) and wide viewing angle was realized.

33.1: A 3.2‐in. LCD Panel using Amorphous Silicon TFT Formed with Novel Selective and Dispersive Transfer Technique

A novel formation process for TFT using our proposed novel selective transfer technique, which enables low cost TFT fabrication on a large and flexible substrate, is proposed. This technique is used to fabricate a 3.2-inch LCD Panel using amorphous silicon TFT transferred on glass substrate for the first time.

LP‐4: Late‐News Poster: Reflective Color Image‐Memory LCD Using Ferroelectric Film on LC Glass Substrate

A 2.8″-diagonal reflective image-memory LCD using ferroelectric film for memory elements, which enables ultra-low-power consumption, is fabricated on a glass substrate for the first time. The asymmetrical feature of the hysteresis loop is improved by symmetrical ferroelectric capacitor configuration, and achieved an image-memory color LCD with good quality.