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

Abstract

Abstract— 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.

High-Performance Solution-Processed Amorphous InGaZnO Thin Film Transistors with a Metal–Organic Decomposition Method

“…Due to high charge carrier mobility and high optical transparency, InGaZnO (IGZO) have attracted considerable interest from the electronic industry for application for thin film transistors (TFT) display backplanes [1][2][3][4][5][6][7][8]. Recently, the IGZO films are deposited typically by magnetron sputtering deposition, or/and chemical vapor deposition (CVD), or/and atomic layer deposition (ALD) processes.…”

“…The solution of metal acetylacetonates (In(acac) 3 , Zn(acac) 2 and Ga(acac) 3 ) is adopted as the precursor. The IGZO films are deposited by spin-coating and then annealed at moderate process temperature (≤500 ∘ C) in air.…”

A printed aluminum cathode with low sintering temperature for organic light-emitting diodes

“…We found the ink based on isopropyl ether (O(C 3 H 7 ) 2 ) to be particularly effective in achieving compact Al lms at relatively low temperature, and this ether is safer in use than the more familiar diethyl ether (O(C 2 H 5 ) 2 ), which is highly ammable even at À5 C, as mentioned by Schmidt et al 16 In addition, Al lms prepared using AlH 3 [O(C 4 H 9 ) 2 ] can be successfully formed at 110-150 C. 14,15 On the other hand, this temperature is still too high for some exible substrates and organic active layers, as mentioned above, and we therefore adopted the highly volatile but easily manipulated solvent O(C 3 H 7 ) 2 for printing the Al cathode, giving a sintering temperature of 80 C.…”

“…Apart from these signals, there were no other signicant peaks. This conrmed both the purity of the Al precursor, and the chemical structure of the Al precursor ink as AlH 3 …”

“…In addition, due to the highly oxidative conditions encountered during the preparation of Al nanoparticles or inks in air, an Al 2 O 3 shell between 3 and 10 nm thick is inevitably present on the surface of the Al particles, giving low electrical conductivity. 14 Recently H. M. Lee 14,15 has proposed the use of an Al solution process for stamping Al cathodes using an ink based on AlH 3 [O(C 4 H 9 ) 2 ]. In the presence of a Ti(O-i-Pr) 4 catalyst and an inert atmosphere this Al compound is converted at 150 C into an Al lm.…”