Sputtered zinc oxide thin films deposited on polyimide substrate and annealing effect on the physical characteristics

Transparent, uniform and adherent ZnO thin films were obtained using radio frequency magnetron sputtering. These films were deposited onto kapton substrates with various thicknesses. Following deposition, some of the ZnO thin films were annealed at different temperatures in air. The morphological structure of ZnO thin films, annealed and as-deposited, was studied using modern methods such as: X-ray photoelectron spectroscopy, X-ray diffraction (XRD) and atomic force microscopy. It was noticed that structural and optical properties of these films depend both on the deposition conditions, annealing temperature and the nature of the used substrate. Therefore, XRD studies showed a polycrystalline structure and a hexagonal symmetry for the obtained thin films. The crystalline structure of the annealed ZnO films exhibited strong orientation along the c axis, with the (002) plane parallel to the kapton substrate. The electrical conductivity of these films, before annealing, has a value between 1.63 and 2.48 x 10(-4) Omega(-1) cm(-1). The optical analyses were investigated by measuring the transmittance curves that were used to find the optical bandgap energy. Post-deposition annealing of the ZnO/kapton samples led to an increase in the optical bandgap from 3.19 to 3.24 eV, emphasizing that annealing and nature of the substrate influence the characteristics of the thin film. (C) 2013 Elsevier B.V. All rights reserved.