Solution‐processed oxide semiconductors for low‐cost and high‐performance thin‐film transistors and fabrication of organic light‐emitting‐diode displays

High‐performance solution‐processed oxide‐semiconductor (OS) thin‐film transistors (TFTs) and their application to a TFT backplane for active‐matrix organic light‐emitting‐diode (AMOLED) displays are reported. For this work, bottom‐gated TFTs having spin‐coated amorphous In‐Zn‐O (IZO) active layers formed at 450°C have been fabricated. A mobility (μ) as high as 5.0 cm2/V‐sec, −0.5 V of threshold voltage (VT), 0.7 V/dec of subthreshold swing (SS), and 6.9 × 108 of on‐off current ratio were obtained by using an etch‐stopper (ES) structure TFT. TFTs exhibited uniform characteristics within 150 × 150‐mm2 substrates. Based on these results, a 2.2‐in. AMOLED display driven by spin‐coated IZO TFTs have also been fabricated. In order to investigate operation instability, a negative‐bias‐temperature‐stress (NBTS) test was carried out at 60°C in ambient air. The IZO‐TFT showed −2.5 V of threshold‐voltage shift (ΔVT) after 10,800 sec of stress time, comparable with the level (ΔVT = −1.96 V) of conventional vacuum‐deposited a‐Si TFTs. Also, other issues regarding solution‐processed OS technology, including the instability, lowering process temperature, and printable devices are discussed.