Mechanical Integrity of Hybrid Components used in Flexible Optoelectronic Devices
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1075-J04-04
Mechanical Integrity of Hybrid Components used in Flexible Optoelectronic Devices Konstantinos A Sierros1,2, Nicholas J Morris1, J Stuart Abell2, Darran R Cairns1,2, and Stephen N. Kukureka2 1 Mechanical and Aerospace Engineering, West Virginia University, Evansdale Campus, Morgantown, WV, 26506 2 Metallurgy and Materials, University of Birmingham, School of Engineering, Edgbaston, Birmingham, B15 2TT, United Kingdom ABSTRACT Fabrication of truly flexible optoelectronic devices, such as flexible displays and flexible photovoltaics, is highly dependent on the mechanical integrity of individual thin inorganic/organic hybrid device components. A common feature of almost all thin composite film components for flexible optoelectronic applications is indium tin oxide (ITO) coated on polyester. The mechanical mismatch of the ITO ceramic coating, a few tens of nm thick, with the polyester, either polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), 125 µm thick, causes the flexible functional structure to fail at moderately low strains under various, externally applied, stress states. It is therefore important to assess the mechanical integrity of such hybrid systems experimentally. We report on the electromechanical behavior of such hybrid systems. INTRODUCTION Under the influence of an externally applied tensile stress, the ITO conductive layer cracks and start losing its functionality between 2 and 2.5% tensile strain [1]. When ITO coated PET is bent, the ITO surface is in tension and it cracks at around 1.2% [2]. Also, under buckling conditions the flexible thin component is observed to start losing its functionality when the externally applied uniaxial compressive strain is between 1.1 and 1.7% [3]. Additionally, when the ITO, deposited on polyethylene naphthalate (PEN), is subjected to an externally applied biaxial tension, the ITO cracks at around 1.4% biaxial strain [4]. Cyclic mandrel loading of ITO coated PET flexible anodes has also been conducted, and three distinct regimes of electrical resistance increase are observed. It is also shown that the change in resistance with temperature is a thermally activated process [5]. Furthermore, amorphous ITO can be etched by acid containing polymer layers such as pressure sensitive adhesives (PSA) [6]. In flexible optoelectronic multilayer stacks, pressure sensitive acrylic acid adhesive layers are usually placed on top of the ITO layer. The combined effect of etching and externally applied stress can lead to stress corrosion cracking of the conductive and transparent layer. This phenomenon is little studied and is important, in electronic device packaging terms, since acid containing layers are present in optoelectronic thin structures such as in organic light emitting displays (OLEDs) [7].
EXPERIMENT Various commercially available ITO films sputtered on different PET and PEN substrates (DuPont Teijin Films Ltd.) were tested monotonically and cyclically under uniaxial tension and compression using a commercial Instron (5500 series) tensile te
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