Hexaaqua Metal Complexes for Low-Temperature Formation of Fully Metal Oxide Thin-Film Transistors

Abstract

We investigated aqueous metal complex-based oxide semiconductor films formed with various ligands, such as chloride, acetate, fluoride, and nitrate. Nitrate ligand-based indium(III) precursor was easily decomposed at low temperature due to the replacement of all nitrate ions with water during solvation to form the hexaaqua indium(III) cation ([In(H 2 O) 6 ] 3+ ). Hexaaqua indium(III) cation was a key complex to realize high-quality oxide films at low temperature. Additionally, Al 2 O 3 -based high-k dielectric was also employed by using a nitrate precursor, and the hexaaqua aluminum(III) cation ([Al(H 2 O) 6 ] 3+ ) was confirmed. This complex-based Al 2 O 3 film showed high breakdown voltage and stable capacitance under high frequency operation compared to organic solvent-based Al 2 O 3 films. We successfully demonstrated aqueous-based In 2 O 3 TFTs with Al 2 O 3 high-k gate dielectrics formed at 250°C with a wide gate voltage operation and high saturation mobility and on/off ratio of 36.31 ± 2.29 cm 2 V −1 s −1 and over 10 7 , respectively. ■ INTRODUCTIONAmorphous metal oxide semiconductor (AOS)-based electronic devices have been developing rapidly for use as thin-film transistors (TFTs) in display backplanes, sensors, and logic devices. 1−3 In particular, the high field-effect mobility (>10 cm 2 V −1 s −1 ), transparency, and electrical stability of AOS TFTs are attractive for flexible transparent circuit applications. Recent research has focused mainly on developing new materials with high mobility and stability, diverse substrates, and facile processing methods. 4,5 Various processing methods are used to deposit AOS such as atomic layer deposition, pulsed laser deposition, sputtering, and solution process. Except for the solution process, most processes are associated with the high cost and the use of vacuum facilities. In order to consider this issue, solution processing has emerged as a future technology with simple process and low cost. Although solution processing of AOS TFTs has great potential, the electrical properties of these devices strongly depend on the processing temperature, and their electrical performances are much lower than that achieved with vacuum processing even after annealing over 450°C. To overcome this obstacle, several solutions have been proposed, including new material synthesis, 6−8 different ligandbased precursor optimization, 9 nanostructure-based film formation, 10,11 ultraviolet (UV) irradiation, 12 high pressure annealing, 13 microwave irradiation, 14 and ozone treatment. 15 A recent study of metal oxide film formed by the aqueous route showed the possibility of a low-temperature process by reducing the amount of carbon-based organic solvent, additives, and ligands in the metal precursors to lessen the detrimental effects of carbon impurities. 16,17 On the basis of an aqueous system, many kinds of metal precursors with different ligands could be selected to form metal oxide formation such as metalbased nitrate, acetate, chloride, fluoride, iodide, and so on. Besides, aqueous...

Printable Semiconductors for Backplane TFTs of Flexible OLED Displays

“…The low‐temperature feature of this method originates from the weak coordination bond (i.e., electrostatic reaction) between the metal cation and neighboring aquo ion. The connection can be easily broken at lower temperatures compared with the covalent bonding in conventional organic‐based precursors . Optimized In 2 O 3 TFTs on flexible PEN substrates were obtained by annealing at 200 °C, yielding a reasonable μ FE of 3.14 cm 2 V −1 s −1 , a high I on / I off over 10 9 , and a voltage shift of 1.47 V with 10 4 s of positive gate bias stress.…”

“…To deposit high‐quality oxide thin films from solution at low temperatures, the selection of metal salt precursors is crucial for the reaction trigger, impurity decomposition, and oxide framework formation. By using thermogravimetric analysis, nitrate precursors were demonstrated to possess the lowest decomposition temperature (≈200 °C) compared with other types, such as chloride, acetate, and fluoride . However, some metal nitrates are unstable and difficult to handle, such as those of Sn, Zr, Hf, and Sb .…”

P-6: Aqueous Precursor Based Solution-Processed Metal Oxide Semiconductor

“…Details can be found in our previous publications. [7,8] For redox reaction, 221.1 mg of indium chloride (InCl 3 , Aldrich, 99.999%) and 0.0861 g of perchloric acid (HClO 4 , Aldrich, ACS reagent, 60%) are added into 10 mL of water. 2-Methoxyethanol (2-ME) solution was synthesized by adding 0.05 mL of ammonium hydroxide (NH 4 OH, 28.0%, Aldrich, 99.99%), 0.05 mL of acetylacetone (AcAc, Aldrich, 99%) and 300 mg of indium nitrate hydrate (In(NO 3 ) 3 ·xH 2 O, Aldrich, 99.999%) into 10 mL 2-ME.…”

All‐Solution‐Processed Metal Oxide/Chalcogenide Hybrid Full‐Color Phototransistors with Multistacked Functional Layers and Composition‐Gradient Heterointerface

“…However, rare‐metal oxide semiconductors and organic/nanoscale‐inorganic semiconductors have still been utilized for carrier transport and visible‐light absorption in all‐solution‐processed hybrid structures . Moreover, most precursor solutions for large‐area compatible solution processes such as sol‐gel, chemical bath deposition (CBD), and electrodeposition have corrosive acidic/basic chemical properties . Therefore, selection of alternative functional materials (rare‐metal‐free high‐mobility oxide semiconductor and high‐efficiency inorganic photoabsorber), suppressed charge trap sites, and chemically stable solution process should be considered to realize all‐solution‐processed metal oxide/chalcogenide semiconductor‐based multistacked visible‐light photo‐TRs for fast dynamic and full‐color photodetection.…”