Solution-Processed Indium-Zinc Oxide Transparent Thin-Film Transistors

Abstract

Transparent thin-film transistors ͑TTFTs͒ with an indium-zinc oxide ͑IZO͒ active layer by the solution-processed deposition method were fabricated and their TFT characterization was examined. Solution-processed IZO thin films were amorphous and highly transparent with Ͼ90% transmittance in the visible region with an optical bandgap of 3.1 eV. Spin-coated IZO TTFTs were operated in depletion mode and showed a field-effect mobility as high as 7.3 cm 2 /V s, a threshold voltage of 2.5 V, an on/off current ratio greater than 10 7 , and a subthreshold slope of 1.47 V/decade. Metal-oxide thin films have been traditionally used as insulators, dielectrics, and conductors in ͑opto͒electronic devices. Recently, metal-oxide thin films have been intensively studied to be applied as transparent semiconducting active layers in transparent thin-film transistors ͑TTFTs͒. Transparent oxide semiconductors ͑TOSs͒ have many advantages compared to silicon or organic semiconductors. TOSs are transparent in the visible region due to their large bandgap and have environmental stability and high field-effect mobility comparable to that of polycrystalline silicon. 1,2 Many TOSs such as ZnO, 3,4 zinc-tin oxide ͑ZTO͒, 5,6 indium-zinc oxide ͑IZO͒, 7-9 and indium-gallium-zinc oxide ͑IGZO͒ 2,10,11 have been reported for transparent active-channel materials in TTFTs. Several TTFTs using TOSs 12,13 and even fully transparent flexible structures 3,14 have been reported. TTFTs based on TOSs are considered to be an alternative to amorphous Si TFTs. However, TOSs are generally prepared by vacuum-deposition methods such as rf magnetron sputtering and pulsed laser deposition. Vacuum-deposition methods require expensive equipment and result in high manufacturing costs.Solution-processed thin-film deposition methods could offer many advantages such as simplicity, low cost, and high throughput that enable the fabrication of high-performance and low-cost electronics. In addition, solution-processed deposition methods such as screen printing, inkjet printing, and imprinting offer the possibility of the direct patternability of TOS thin films which could replace the conventional photolithographic technique. Recently, ZnO, 15-17 ZTO, 18 and IZO-based 19 TTFTs fabricated by solution-processed deposition using metallorganic or metal halide precursors in various solvents were reported to have high mobility up to ϳ16 cm 2 /V s and to give direct patternability. However, in the case of using metal chloride as precursors, the presence of chloride ions during heattreatment of the film is unfavorable under certain circumstances. In addition, TTFTs fabricated by solution-processed deposition showed high off currents and a low on/off current ratio compared to the vacuum-deposited TTFTs.In this article, we report the amorphous IZO semiconductor thin films fabricated by solution process under ambient air conditions using metal acetates as precursors and the performance of TTFTs with an amorphous IZO active layer. Spin-coated IZO thin film was uniform, highly transparent...

An ‘aqueous route’ for the fabrication of low-temperature-processable oxide flexible transparent thin-film transistors on plastic substrates

“…An aqueous route allows for the preparation of IZO TFTs at a lower temperature compared with that used in the previously reported 2-methoxyethanol-based approach. [10][11][12] To investigate the uniformity of the devices, 36 TFTs with an IO active layer prepared via the aqueous route were fabricated at an The storage stability of a precursor solution is an important issue in sol-gel chemistry. The TFTs fabricated from pristine and 100-day-old aqueous solutions were compared with investigate the storage stability of the aqueous solution.…”

“…The high annealing temperature, which is usually 4400 1C, is not compatible with flexible plastic substrates, with conventional glass or with the stacked multi-layer structures because of the mismatch in the coefficient of thermal expansion between the layers during deposition. [10][11][12] A few studies on low-temperatureprocessable MOSs have been reported. [13][14][15][16] However, the authors of these studies used either complex and unstable precursors that required significant effort and multiple steps for synthesis or complicated chemical reactions that are not appropriate for the general fabrication technique.…”

Novel ZrInZnO Thin‐film Transistor with Excellent Stability

“…There have been many reports of high-performance TFTs with oxide semiconductors, including ZnO, [8][9][10] InZnO, [11][12][13] ZnSnO, [14] and InGaZnO [15][16][17][18][19] as the channel materials. The field-effect mobilities (m FE ), sub-threshold gate swing (S), and I on/ off ratios of ZnO-based TFTs have been dramatically improved since Hosono and coworkers reported the usage of amorphous InGaZnO as a channel material using physical-vapor-deposition techniques.…”

Effects of Post-Deposition Annealing Atmosphere and Duration on Sol-Gel Derived Amorphous Indium-Zinc-Oxide Thin-Film Transistors

“…A precursor solution of Zn(CH 3 COO) 2 ·2H 2 O with limited solubility in alcohols is easily precipitated or gelled, while In(CH 3 COO) 3 is not soluble in 2-ME. Both 0.4 M of Diethanolamine (DEA) and 0.4 M of acetylacetone were utilized to stabilize the IZO precursor solution (18,19). The channel width and length of all a-IGZO TFTs were 500 μm and 50 μm, respectively.…”