Thin Film Metal Oxide Semiconductors Deposited on Polymeric Substrates
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Thin Film Metal Oxide Semiconductors Deposited on Polymeric Substrates Elvira Fortunato1, Patrícia Nunes1, António Marques1, Daniel Costa1, Hugo Águas1, Isabel Ferreira1, Maria E. V. Costa2 and Rodrigo Martins1 1 Department of Materials Science/CENIMAT, Faculty of Sciences and Technology, New University of Lisbon and CEMOP-UNINOVA, 2825-114 Caparica, Portugal 2 Department of Ceramics and Glass Engineering/UIMC, University of Aveiro, 3810-193 Aveiro Portugal ABSTRACT Highly textured transparent conducting ZnO:Al thin films have been prepared by r.f. magnetron sputtering. The films were deposited on polyester (Mylar type D, 100 µm thickness) and glass substrates at room temperature. Surface stylus profiling, X-ray diffraction, scanning electron microscopy, transmission electron microscope and Hall effect measurements as a function of temperature have been used to characterize the produced films. The samples are polycrystalline with a hexagonal wurtzite structure and a strong crystallographic c-axis orientation (002) perpendicular to the substrate surface (columnar structure). The ZnO:Al thin films with a resistivity as low as 3.6×10-2 Ωcm have been obtained, as deposited. INTRODUCTION Transparent conducting oxide (TCO) thin films have many applications due to their unique properties of low electrical resistivity and high optical transmittance. A number of materials such as indium tin oxide (ITO), tin oxide (SnO2), zinc oxide (ZnO) and cadmium stannate (Cd2SnO4) have been used in many applications, like: anti-static coatings, heat mirrors, solar cells, flat panel displays, sensors, organic light emitting diodes, etc [1]. Nevertheless, ZnO thin films are nowadays of much interest in science and technology due to their advantageous properties, when compared to the other mentioned TCO’s, like: low cost material; relatively low deposition temperature (even at room temperature); high stability in hydrogen plasmas such as that used in the fabrication of solar cells and presents non-toxicity. Many techniques have been employed to produce doped ZnO based coatings, e.g r.f magnetron sputtering [2, 3], chemical vapour deposition [4, 5], spray pyrolysis [6, 7], sol-gel [8, 9], atomic layer deposition [10] and laser deposition [11]. Among these techniques, the r.f. magnetron sputtering has proved to be the best one to produce ZnO based films at room temperature [12]. In this paper we present results on transparent conducting Al doped ZnO deposited by rf magnetron sputtering on polyester substrates with 100 µm thickness and glass substrates. Although these oxides have been extensively studied on glass substrates [1], no detailed work has been reported on polymeric substrates. Nowadays there is a great interest in replacing glass substrates with polymer substrates, particularly in flat panel display technology [13], where low volume, lightweight, and robustness are relevant. Besides that the added flexibility of polymeric substrates opens new application fields that utilize curved surfaces, like for example, large area flexible posi
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