Abstract
Hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) and amorphous indium-gallium-zinc oxide (a-IGZO) TFTs have been widely used in the gate driver circuits and pixel circuits of the active-matrix liquid crystal displays due to their higher uniformity, lower manufacturing cost, and lower leakage currents than low-temperature polycrystalline (LTPS) TFTs. Moreover, a-IGZO TFTs have higher mobility than a-Si:H TFTs, and thus pixel circuits based on a-IGZO TFTs can enhance driving capability, decreasing the overall layout area. Nevertheless, both a-Si:H and a-IGZO technologies only have n-type TFTs, so the complementary metal-oxide-semiconductor (CMOS) circuits cannot be implemented by them directly. Furthermore, a-Si:H and a-IGZO TFTs have the severe threshold voltage shift which results from bias under long-term stress. In summary, the aforementioned issues must be considered in the design of the gate driver circuit and the pixel circuit using n-type TFTs.This thesis proposes two a-Si:H gate driver circuits and one a-IGZO pixel circuit of blue phase liquid crystal displays (BPLCDs), and the feasibility of the proposed circuits is verified by the HSPICE simulator. The first a-Si:H gate driver circuit, consisting of eight TFTs and three capacitors, is suitable for high-resolution panels. The gate node of the driving TFT is bootstrapped twice to a higher voltage level by the capacitive coupling effect, so the output node can be discharged faster to a low voltage level. According to the simulation results, the falling time of the output waveform is only 1.42 μs when the capacitance of two storage capacitors is chosen properly. The second a-Si:H gate driver circuit is composed of 12 TFTs and three capacitors for use in in-cell touch panels. To increase the report rate and prevent display-to-touch crosstalk (DTX), the display operation stops eight times to perform touch sensing period in the frame time. In this work, the driving TFT is turned off to suppress the threshold voltage shift during the touch sensing period. Based on the simulation results, stable output waveforms are successfully generated before and after the touch sensing period. The third proposed design is a simple pixel circuit that comprises three a-IGZO TFTs and two capacitors for use in BPLCDs. The coupling method is utilized to produce the wide output voltage range that is twice the data voltage range supplied by the source driver integrated circuit. Simulation results show that the output voltage range of 0.342 V to 29.6 V can be achieved with a 0 V to 15 V input voltage range.
| Date of Award | 2016 |
|---|---|
| Original language | Chinese (Traditional) |
| Supervisor | Chih-Lung Lin (Supervisor) |