Mechanics of Indium-Tin-Oxide Films on Polymer Substrates with Organic Buffer Layer
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Mechanics of indium-tin-oxide films on polymer substrates with organic buffer layer Sung Kyu Park, Jeong In Han, and Won Keun Kim Korea Electronics Technology Institute, Pyungtaek, Kyunggi. 451-860, Korea ABSTRACT This study was undertaken to derive the understandings of the electro- mechanical properties of ITO films on highly elongated polymer substrates which were subjected to thermally and mechanically stresses. The substrates are polycarbonate foils with 100, 180 and 200-µm thicknesses with gas barrier layer on their bottom surface. The metallic films used in the experiments are indium- tin-oxide (ITO) and tantalum (Ta) films. Strain- gauge measurements and numerical analyses using modified Stoney formula were carried out to determine the electro-mechanics in ITO films. The numerical analyses and empirical results show the thermally and externally induced mechanical stresses in ITO films on polymer substrates are responsible for the difference in thermal expansion between the ITO films and the substrate and for substrate material and thickness, respectively. Therefore, a ramped heating processing and a buffer layer were employed to improve the electro- mechanics, and then, the effects of the buffer layer were also quantified in terms of conductivity-strain variations. INTRODUCTION For more than a decade now, organic electron devices based on polymer substrates have been envisioned as a viable alternative to more traditional, mainstream electron devices based on inorganic substrates such as glass and silicon substrates [1-2]. Hence, organic thinfilm devices have been studied extensively and thus the tremendous progress in performance of these devices has been achieved [3-4]. There are many problems, however, such as stressed-induced electro-mechanics of metallic films, interfacial mismatch of between organic and inorganic materials, chemical compatibility of the hybrid materials, and etc. Most of all, stress- induced mechanical degradation of metallic films are considerably researched, since it is connected with the device performance directly [5-7]. In this paper, in addition to the novel methods for reduction of thermal stress in ITO films, we present a new physical model of the externally induced mechanical stress taking into account a neutral layer which is stress free layer in a film-substrate couple. To lessen the externally induced mechanical stress, we employ a buffer layer which is inserted between the metallic films and the polymer substrates, and then the effects of the buffer layer are extensively studied with numerical analyses and experimental results. The detailed experimental setup and results of the deposition of the reliable ITO or metal films and other processing concerning the polymer substrates have been reported earlier [8-10].
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EXPERIMENTAL DETAILS Rf- magnetron and DC sputtering system, which were modified for these studies, performed the deposition of metallic films on the polymer substrates. The metallic materials used in these experiments are indium-tin-oxide (ITO) and tantalu
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