Abstract
In recent years, hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) and amorphous indium-gallium-zinc oxide thin-film transistors (a-IGZO TFTs) integrated in active-matrix liquid crystal displays (AMLCDs) have become the mainstream because of the low-cost fabrication and better uniformity over large-area substrates. However, the severe threshold voltage (VTH) shifts of a-Si:H TFTs and a-IGZO TFTs lead to the instability of gate driver and pixel circuits. Additionally, AMLCDs integrated with in-cell touch structure have attracted considerable attention. However, when the display driving and the touch sensing operate simultaneously, the display signals interfere in the sensed touch signals by parasitic capacitive coupling. This is defined as display-to-touch crosstalk (DTX). Consequently, solving the DTX has become an intensive issue for in-cell touch panels. Among AMLCD technologies, blue-phase liquid crystal (BPLC) is regarded as a next-generation technology for displays because it provides sub-millisecond response time, alignment-layer-free process, and wide viewing angle compared to LC. However, high operating frequency of the pixel circuit causes a decrease in the dielectric constant of BPLC. This phenomenon is called the high frequency effect. Therefore, the voltage variations across BPLC during the emission period lead to incorrect gray levels in displays.This thesis proposes two a-Si:H gate driver circuits and an a-IGZO BPLC pixel circuit. The feasibility of the proposed circuits is verified through an HSPICE simulator and experimental results. The first gate driver circuit uses four-phase overlapping clock signals and the proposed pull-down circuit to reduce the leakage current when generating the output waveforms, maintaining high driving capability of driving TFT. Measurements-made during a high-temperature reliability test over 720 hours indicate that the output waveforms of the proposed circuit are highly stable. The second gate driver circuit is designed for use in in-cell touch panels. The proposed circuit pauses the operation of the display driving to support touch sensing operations several times per frame and then re-starts the display operation again. Simulation results indicate that the variations of rising time and falling time of output waveforms before and after touch sensing operation are 3.71% and 0.24%, respectively, when the VTH of re-charge TFT shifts by 10 V. The third circuit is a pixel circuit for high-resolution and high-frame-rate BPLC displays. With an inverter structure, the circuit generates saturation current to charge BPLC continuously, ameliorating the high frequency effect of BPLC. During the emission period, the circuit turns off all TFTs to avoid leakage current flowing into BPLC. The simulation results indicate that the proposed circuit achieves stable and uniform output characteristics even if the VTH of a-IGZO TFTs shifts by ±1.5 V.
| Date of Award | 2016 |
|---|---|
| Original language | Chinese (Traditional) |
| Supervisor | Chih-Lung Lin (Supervisor) |