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 degrees C have been fabricated. A mobility (mu) as high as 5.0 cm(2)/V-sec, -0.5 V of threshold voltage (V-T), 0.7 V/dec of subthreshold swing (SS), and 6.9x10(8) of on-off current ratio were obtained by using an etch-stopper (ES) structure TFT. TFTs exhibited uniform characteristics within 150 x 150-mm(2) 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 degrees C in ambient air. The IZO-TFT showed -2.5 V of threshold-voltage shift (Delta V-T) after 10,800 sec of stress time, comparable with the level (Delta V-T = -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.