투명 플렉시블 디스플레이용 IGZO 박막 트랜지스터의 층간절연막에 따른 특성 연구

Abstract

Active-matrix organic light-emitting diode (AMOLED) displays have been widely developed as ideal flat-panel displays due to their wide viewing angle, high brightness, fast response time, compactness, light weigh, vivid color, and high contrast ratio. Despite these advantages, however AMOLED display still have problems with regard to large-display applications, such as in computer monitors and televisions. The main issue of large AMOLED displays is their backplane, for which hydrogenated amorphous silicon (a-Si:H) and low-temperature polycrystalline-silicon (LTPS) are currently being used.

The a-Si:H TFT technology has the advantages of uniform electrical characteristics (e.g. mobility and threshold voltage), low-cost process, and large glass size because it does not require the ion-doping process and crystallization, but a-Si:H TFTs have critical drawbacks when used in the actual backplanes of AMOLED displays. As the field effect mobility of a-Si:H TFTs have poor stability: their threshold voltages shift under constant current stress. On the other hand, LTPS TFTs have high field effect mobility and excellent stability, but crystallization is needed to convert a-Si:H to LTPS TFTs, and this process has a high cost. Moreover, as LTPS TFTs have grain boundaries, their threshold voltages are not uniform. This is overcome by using complex compensation pixels, which have a low yield and a high cost. Therefore, a-Si:H and LTPS backplanes are not suitable for large AMOLED displays.

Recently, indium gallium zinc oxide TFTs were developed for use in the backplanes of AMOLED displays because they have various advantages compared to a-Si:H and LTPS TFTs. IGZO TFTs have higher field effect mobility than a-Si:H TFTs. As such, they have good driving capabilities, which can enable them to drive large displays. IGZO TFTs also have higher current on/off ratios as well as better stability under constant current stress than a-Si:H TFTs do.

Moreover, they can be fabricated using a lower-temperature process and have less processing steps compared with LTPS TFTs.

In this work, we investigate amorphous indium-gallium-zinc-oxide thin-film-transistors (a-IGZO TFTs). The effects of the interface between the IDL and IGZO channel on the electrical properties of a-IGZO TFTs were simulated. Two kinds of IDLs were analyzed, which were aluminum oxide and silicon nitride. And then we fabricated a-IGZO TFTs with optimized parameters.