Electro-structural and Film Growth Properties of Room-temperature Deposited Indium-Tin-Oxide on Polymer Substrates
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Electro-structural and Film Growth Properties of Room-temperature Deposited Indium-Tin-Oxide on Polymer Substrates Sung Kyu Park, Jeong In Han, Dae Gyu Moon, Won Keun Kim, and Min Gi Kwak Information Display Research Center, Korea Electronics Technology Institute, Pyungtaek, Kyunggi, Korea. ABSTRACT Electrical and structural properties of indium-tin-oxide (ITO) films on flexible polymer substrates were investigated. Room temperature sputtered ITO films on polymer substrates are initially amorphous but become partially crystalline as oxygen partial pressure decreases under 1.5%. The crystallinity shows more (400) and (222) preferentially oriented textures as decreasing of oxygen pressure resulting in lower resistivity. Moreover, an interesting growth property similar to 3D growth mechanism including larger grain size and columnar-like grain structure was also observed. It is considered that the columnar-like grain structure is probably attributed to the poor surface morphology of polymer substrates Based on the experiments, we obtained high performance ITO films on a polycarbonate substrate including 3.8 x 10 –4 Ω-cm in resistivity and transmittance above 80% in the visible ranges at 0.2% oxygen partial pressure. INTRODUCTION Indium-tin-oxide (ITO) is frequently used in optoelectronic devices that require high electrical conductivity and high transparency in the visible region. Nowadays, optoelectronic devices, based on polymer substrates using organic material as an active layer such as organic transistors and OLEDs, have been envisioned as a viable alternative to traditional optoelectronic devices [1-4]. However, the lower thermal tolerance of polymer substrate and organic material need very low temperature process inevitably. Therefore, recent technical trend in the fields has favored low temperature deposited ITO films with high conductivity. In this research, we studied the electrical, structural and optical properties of ITO film deposited on polymer substrate and its time-dependent film growth properties concerning electrical performance. EXPERIMENTAL DETAILS Deposition of ITO films on polymer substrates was performed by rf-magnetron sputtering system which was modified for these studies. The ITO target used for these experiments was 10 wt% SnO2 doped In2O3 with 4-inch diameter. The distance between the target and the substrate was about 60 mm (T-S). Preliminary, polycarbonate (PC) and polyethersulfone (PES) substrates (100 µm-thickness) were pre-annealed at 120°C for the reduction of polymer shrinkage and sequent deposition process was preceded in the mixture of argon and oxygen gases by controlling with a mass flow meter. The oxygen partial pressure was varied from the minimum (0%) up to a level at which no evident changes observed (15%). Base pressure of the sputtering system was 1 x 10-7 Torr, the process pressure was 3.5 x 10-3 Torr and the sputtering power
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applied to the process was 100 W. The film thickness was measured by thickness profiler and controlled by the adjustment of depositi
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