Enhancement of the Electrical Properties of ITO Deposited on Polymeric Substrates by Using a ZnO Buffer Layer
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Enhancement of the Electrical Properties of ITO Deposited on Polymeric Substrates by Using a ZnO Buffer Layer E. Fortunato, A. Gonçalves, C. Nunes de Carvalho, A. Pimentel, G. Lavareda, A. Marques, R. Martins Materials Science Department/CENIMAT, Faculty of Sciences and Technology of New University of Lisbon and CEMOP/UNINOVA, Campus da Caparica, 2829-516 Caparica, Portugal.
ABSTRACT In this paper we present the effect of the insertion of a non-doped nanocrystalline zinc oxide/buffer layer on the electrical, optical and structural properties of indium tin oxide produced at room temperature by radio frequency plasma enhanced reactive thermal evaporation on polymeric substrates. The electrical resistivity of the ITO films is reduced by more than two orders of magnitude (4.5×10-1 to 2.9×10-3 Ωcm). From the Hall effect measurements it is observed that the large decrease associated to the electrical resistivity, is due to the increase associated to the Hall mobility. Concerning the optical properties no effect was observed, being the transmittance in the visible and near the infra red region always higher than 80%.
INTRODUCTION Nowadays flexible electronics is an emerging and multidisciplinary research topic in several areas including for example flat panel displays and organic electronics [1]. Polymer substrates suitable for these applications are being developed. However, polymers are very sensitive, to moisture and oxygen and some of them are even chemically unstable when used with thin film technologies. Transparent diffusion barrier coatings have been extensively researched in order to provide a smooth surface and reduce the diffusion of water vapour and oxygen into displays laid down on polymer substrates. However, defects on the relatively rough surface of polymers, can cause pinholes in the final coating and lead to catastrophic failure of barrier properties. For this work, thin ZnO barrier coatings were deposited by rf magnetron sputtering on PEN substrates (included in the group of semi-crystalline polymers), at room temperature, to protect the substrates surface of contamination from water and moisture diffusion [2]. The strong preferred orientation (002) of the ZnO films is also an advantage in order to induce an increase of ITO films grain size, reducing electron scattering. ITO thin films were deposited on those PEN substrates with and without a ZnO barrier at room temperature by rf plasma enhanced reactive thermal evaporation. High quality ITO films at lower deposition temperatures are essential to substitute glass substrates for polymer foils. In this paper a detailed description of the preparation conditions as well as on the electrical (Hall effect), optical (transmittance), structural (X-ray diffraction) and morphological (FE SEM) properties will be presented.
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EXPERIMENTAL DETAILS ITO thin films were deposited on polyethylene naphthalate – PEN substrates coated with ZnO layers by an improved radio frequency plasma enhanced reactive thermal evaporation (rfPERTE) of a 85%In-15%Sn allo
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