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

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.