Effects of Drying Temperature on Surface Morphology and Electric Behavior of IGZO Thin Film Prepared by Solution Process
- PDF / 125,398,163 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 76 Downloads / 183 Views
Effects of Drying Temperature on Surface Morphology and Electric Behavior of IGZO Thin Film Prepared by Solution Process Nobuko Fukuda, Shintaro Ogura, Koji Abe, 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 have achieved a drastic improvement of the performance as thin film transistor (TFT) for solution-processed IGZO thin film by controlling drying temperature of solvents containing the precursor solution. The IGZO-precursor solution was prepared by mixing of metal nitrates and two kinds of organic solvents, 2-methoxyethanol (2ME) and 2,2,2-trifluoroethanol (TFE). 2ME was used for dissolving metal nitrates. TFE was added as a solvent for reducing surface tension as small as possible, leading to improvement of the wettability of the precursor solution on the surface of the substrate. In order to discuss the relationship between morphology and drying process, the spin-coated IGZO-precursor films were dried at room temperature and 140 ºC on a hotplate, respectively. Annealing of the both films was carried out at 300 ºC in an electric oven for 60 min after each drying process. Drying at room temperature provides a discontinuous film, resulting in a large variation of the TFT performance. On the other hand, drying at 140 ºC provides a continuous film, resulting in the higher TFT performance and a minor variation. The difference in surface morphologies would be derived from the evaporation rate of the organic solvents. The rapid evaporation at 140 ºC brings about rapid pinning of the spin-coated precursor layer on the substrate. Preparation process via the drying at 140 ºC gave ~ 1 cm2 V-1 s-1 of the saturated mobility, quite small hysteresis, and 107~ 108 of the on-off ratio. INTRODUCTION Solution process is a simple method for obtaining metal oxide thin layers without vacuum technology. Recently the solution process has been focused in terms of cost-saving and energy conservation for manufacturing. The research trend to flexible electronics also accelerates improvement of the solution process and the materials. Especially, the precursor materials have been widely developed for satisfying low temperature process. Metal alkoxide is one of the promising materials for obtaining metal oxides [1]. Metal alkoxides provide the highperformance mixed oxide semiconductors such as indium gallium zinc oxide (IGZO) and indium zinc oxide (IZO) from the solution process at less than 250 ºC. The process, however, requires an inert gas atmosphere. Organic solutions containing metal salts are also promising materials as the metal oxide precursors. In this case, thermal process at more than 400 ºC provides the high performance mixed oxide semiconductors (~ 1 cm2 V-1 s-1) in air [2]. That is because decomposition of an amine compound in the organic solution occurs at 300-400 ºC. In other cases, photo-sintering with a xenon flash lamp [3], irradiation of an excimer laser [4], and UVozone treatment
