Characterization of the physical and electrical properties of Indium tin oxide on polyethylene napthalate

Abstract

Indium tin oxide (ITO) thin films, on polyethylene napthalate (PEN) of both good electrical and optical properties were obtained by radio-frequency sputtering. The optoelectronic properties of the ITO films on PEN substrate were evaluated in terms of the oxygen content and the surface morphology. Rutherford backscattering spectrometry analysis was used to determine the oxygen content in the film. Hall-effect measurements were used to evaluate the dependence of electrical properties on oxygen content. The results showed that the resistivity of the ITO film increases with increasing oxygen content. For an oxygen content of 1.6×1018–2.48×1018atoms∕cm2, the resistivity varied from 0.38×10−2to1.86×10−2Ωcm. Typical resistivities were about ∼10−3Ωcm. UV-Vis spectroscopy and atomic force microscopy measurements were used to determine the optical transmittance and surface roughness of ITO films, respectively. Optical transmittances of ∼85% were obtained for the ITO thin films. Our results revealed that substrate roughness were translated onto the deposited ITO thin layers. The ITO surface roughness influences both the optical and electrical properties of the thin films. For a 125μm PEN substrate the roughness is 8.4nm, whereas it is 3.2nm for 200μm substrate thicknesses. The optical band gap is about 3.15eV for all ITO film and is influenced by the polymer substrate. A model is proposed that the optical transmittance in the visible region is governed by the carrier concentration in the ITO thin films.