Dae-won Kim

76.2: Development of Highly Stable a‐IGZO TFT with TiOx as a Passivation Layer for Active‐Matrix Display

Titanium oxide (TiOx) was employed for passivation layer of indium-gallium-zinc oxide (a-IGZO) TFTs. Molybdenum (Mo) and titanium (Ti) was used as a source-drain metal. It is demonstrated the titanium layer could be used as an etch stopper layer to protect the back channel of a-IGZO during Mo etching process and transformed into TiOx by the surface treatment using oxygen plasma. From device measurement, we have observed that Ion/Ioff ratio and mobility are ∼108 and 9 cm2 V−1 sec−1, respectively. AMLCD panel has been demonstrated to verify the device uniformity and performance.

Fine-Patterned Organic Thin Film Transistors using Solution Organic Semiconductor Materials

To integrate solution-processible organic semiconductors in the array of thin-film transistors, fine-patterned organic thin-film transistors were fabricated by photolithography. Gold, which has a high work function, was used as a source–drain electrode to reduce the energy barrier between the organic semiconductor and the source–drain. Stacked double layers of gold and chromium were deposited and etched on a glass substrate to enhance the poor adhesion of gold on glass, and then a self-assembled monolayer was formed on them. Solutions of an organic semiconductor and a low-k organic gate insulator were spun by a spin coater and patterned by dry etching using a gate metal as a mask. The devices fabricated by this method show good electrical properties, average field effect mobilities of 0.2–0.3 cm2 V-1 s-1, and an on/off current ratio of over 105 in device dimensions of W/L=84/6 µm. The leakage current through the gate insulator between the gate and the source–drain was similar to that of SiNx in amorphous silicon thin-film transistor (a-Si TFT), which is lower than 10 pA. When the bias-stress stability of organic thin film transistors (OTFTs) was compared with that of a-Si TFT, the threshold voltage shift of OTFT was comparable to that of a-Si TFT, which is smaller than 1 V. However, the stability of OTFT should be further improved and discussed.

9.3: Control of Threshold Voltage in Back Channel Etch Type Amorphous Indium Gallium Zinc Oxide Thin Film Transistors

Tuning the process pressure at the deposition of the passivation layers has been suggested in the way of controlling the threshold voltage of a-IGZO TFTs, making it possible to employ gate driver integration. It has showed that Vth linearly changes with the pressure ΔVth/ΔPressure∼3.5V/100Pa. A 3.2 inch WVGA AMLCD with integrated gate driver circuits were successfully demonstrated using the enhancement mode BCE type bottom gate a-IGZO TFTs.

High resolution full color liquid crystal display driven by solution-processed organic thin film transistors

We have fabricated a solution processed high resolution (15.0 inch diagonal sized SXGA, 110ppi) organic thin film transistor array to drive the liquid crystal display, where the whole layers except an electrode were formed by organic materials using solution process. The TFT in the array exhibited an average field effect mobility of 0.2∼0.3 cm2/Vs, an on/off current ratio of 106, and obtained good uniformity as well as high mobility of OTFT performance.