Moisture Permeability Through Multilayered Barrier Films as Applied to Flexible OLED Display J. Greener, * K. C. Ng, K. M. Vaeth, T. M. Smith Eastman Kodak Company, Rochester, New York 14650-2158 Received 27 February 2007; accepted 29 March 2007 DOI 10.1002/app.26863 Published online 28 August 2007 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Strict protection of organic light-emitting diodes (OLEDs) and other optoelectronic materials from direct contact with ambient moisture and oxygen is one of the major challenges in the development of flexible OLED displays and other flexible electronic devices. This problem is typically addressed by the use of polymeric substrates with multilayered barrier coatings comprising alternating organic/inorganic layers. The multilayered barrier ap- proach is critically examined using a numerical model based on a defect-dominated diffusion process combined with experiments involving face-to-face lamination of two barrier films. The modeling results identify two regimes, corresponding to two distinct permeation mechanisms, and provide scaling relationships and general design criteria for multilayered barrier coatings. The results suggest that the most significant gain in barrier performance can be realized when the thickness of the organic/adhesive layer(s) in the multilayered structure is less than the average pinhole (defect) size in the inorganic barrier layer(s). Ó 2007 Wiley Periodicals, Inc. J Appl Polym Sci 106: 3534–3542, 2007 Key words: OLED; barrier; film; WVTR; permeability INTRODUCTION One of the major challenges in the development of flexible organic light-emitting diode (OLED) devices is the need to protect the OLED materials from dam- age by ambient moisture and oxygen. These devices require protective layers and encapsulants with ex- tremely low moisture and oxygen permeabilities; moisture permeability of less than 10 26 g/m 2 /day and oxygen permeability of less than 10 23 cc/m 2 / day are generally cited as the minimum values required to assure adequate lifetime stability for most OLED devices. 1 Polymeric materials, however, are inherently porous, having moisture permeabil- ities typically > 1 g/m 2 /day, and are therefore not suitable, in themselves, to provide adequate protec- tion to the OLED materials. One way to lower the permeability of the polymeric substrate is to coat it with an essentially impermeable inorganic layer via an appropriate vacuum deposition process. Such layers, usually comprising oxides, nitrides, or car- bides, are impermeable to moisture and oxygen only if the layer is free of defects. However, defects (‘‘pinholes’’) are inherently present in vacuum-de- posited layers because of imperfections in the depo- sition process (intrinsic defects) or as a result of the presence of impurities in the vacuum chamber or on the coated substrate (extrinsic defects). Thus, even if the substrate is coated with an inorganic barrier layer, the barrier performance of this composite structure is still expected to fall short for OLED applications. General approaches to reduce the num- ber and size of pinholes in inorganic layers include various modifications to the vacuum-deposition pro- cess while paying close attention to cleanliness. With these improvements, the permeability can be signifi- cantly lowered, but it is still unlikely to meet the OLED targets cited earlier. One approach for boost- ing the performance of barrier films was pioneered by several companies in the food packaging industry and further developed for OLED applications by a team from Battelle (now licensed and under devel- opment by Vitex Corp. and known under the trade name of Barix 1 ). This approach involves the creation of a multilayered stack of inorganic layers separated by thin organic layers (typically UV-curable acryl- ates), which allegedly creates a so-called ‘‘tortuous path’’ for the diffusing species, thereby lowering the overall permeability of the film. 2–4 With this general approach Vitex and others claim water vapor trans- mission rates (WVTRs) approaching the 10 26 g/m 2 / day target. However, this method is quite costly and not sufficiently robust. Particularly problematic with this approach are the issues involving acrylate depo- sition and curing, including control of film thickness, particulate formation in the deposition chamber, and health and safety concerns with the acrylate formula- tion. A very similar structure can be fabricated by Correspondence to: J. Greener (jgreener@rohmhaas.com). *Present address: Rohm and Haas Electronic Materials, Rochester, New York 14650. Journal of Applied Polymer Science, Vol. 106, 3534–3542 (2007) V V C 2007 Wiley Periodicals, Inc.