Characteristics of indium–tin oxide thin films grown on flexible plastic substrates at room temperature

Transparent and conductive indium–tin oxide (ITO) thin films were deposited on polyethersulfone (PES) flexible plastic substrates by DC magnetron sputtering. The crystalline structure and optical–electric characteristics were investigated to achieve the optimum room-temperature growth conditions. The crystalline orientation and the surface morphology were characterized by X-ray diffraction (XRD) and the atomic force microscopy (AFM), respectively. The ITO/substrate interfaces were observed by scanning electron microscopy (SEM). In addition, the resistivity, the Hall effect, and the optical transmittance were measured to characterize the photo-electric properties of as grown films. It is found that the ITO films are epitaxially grown with the orientations 〈2 2 2〉, 〈4 0 0〉, and 〈4 4 0〉 perpendicular to the film plane. Moreover, the resistivity of thin film decreases with an increase in the (2 2 2) diffraction intensity. The obtained optimum growth conditions for the room-temperature deposition are: DC power=300 W, deposition pressure=2.0 mTorr, and the gas of Ar:O2=100:1. With the optimum conditions, the resistivity of 6.42×10−3 Ω cm, carrier concentration of 1.13×1019 cm−3, and transmittance of 85% for films grown on PES substrates are obtained. Comparing the results with those reported by other workers, we conclude that improved photo-electric properties of ITO films can be obtained by using the DC magnetron sputtering technique at room temperature.