Effects of Amines on Chemical and Physical Behaviors of Viscous Precursor Sols to Indium Gallium Zinc Oxide
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Effects of Amines on Chemical and Physical Behaviors of Viscous Precursor Sols to Indium Gallium Zinc Oxide Nobuko Fukuda, Shintaro Ogura, Ken-ichi Nomura, and Hirobumi Ushijima Flexible Electronics Research Center (FLEC), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8565, Japan. ABSTRACT We synthesized viscous precursors to indium gallium zinc oxide (IGZO) using three kinds of alcoholamines, ethanolamine (EA), diethanolamine (DEA), and triethanolamine (TEA), by a simple process. The viscous precursors are obtained just by vigorous stirring of alcoholamine and urea in an aqueous solution containing the metal nitrates during heating at 150-160 ºC. The precursor containing EA (EA-precursor) is a pale-orange suspension containing aggregates of the metal hydroxides and shows pseudoplastic flow. The precursors containing DEA (DEAprecursor) and TEA (TEA-precursor) are transparent pale-yellow and dark-orange sols, respectively. They give Newtonian flow in the lower shear rate and pseudoplastic flow in the higher shear rate. Higher concentration of metal salts leads to higher viscosity of the precursors. According to thermogravimetry-differential thermal analysis (TG-DTA) for the EA- and DEAprecursors, evaporation of alcoholamine occurs at around each boiling point and subsequently formation of metal oxides occur at around 300 ºC. In the case of the TEA-precursor, formation of metal oxides occurs before pyrolysis of TEA attributed to the higher boiling point of TEA. The thin IGZO film, which is prepared by spin-coating of the diluted DEA-precursor and subsequent sintering at 450 ºC for 30 min, shows 0.02 cm2 ·V-1s-1 of the mobility and 10-5 of the on/off ratio. The highly viscous DEA-precursor containing high concentration of metal ions allows patterning in an area of 100 cm2 onto a surface of a silicon wafer with screen printing. INTRODUCTION Printing technology has great potentials for low-cost manufacturing of electronic and photoelectronic devices. The advantages of the printing technology include reduction of the number of manufacturing processes such as mask-less patterning, energy conservation, and suitability for manufacturing of flexible devices. Recently various printing processes and printable materials as inks have been widely developed for printed devices [1-3]. The printing methods are deeply related to chemical and physical properties of the inks. Viscosity is one of the key factors for determining the printing method. For example, appropriate viscosity for inkjet printing is lower than that for screen and offset printings. The most important points in development of printable materials are design and synthesis tailored to the desired printing method. Indium-gallium-zinc oxide (IGZO) is an attractive material as a transparent metal oxide semiconductor [4]. Amorphous IGZO films prepared by sol-gel process and sintering show high performance as an n-typed semiconductor of a thin film transistor (TFT) [5]. Typical IGZO precursors are low-viscous sols with ap
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