Material Characterisation of a Novel Permeation Barrier for Flexible Organic Displays
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1007-S07-06
Material Characterisation of a Novel Permeation Barrier for Flexible Organic Displays Jonathan Gartside1, Prashant Mandlik1, Sigurd Wagner1, Teddy Zhou2, Jeff Silvernail2, and Mike Hack2 1 Department of Electrical Engineering, Princeton University, Engineering Quadrangle, Olden Street, Princeton, NJ, 08544 2 Universal Display Corporation, Ewing, NJ, 08618
ABSTRACT Encapsulation for flexible organic light emitting diodes (OLEDs) is an area of active research. Multilayer barriers, with alternating organic and inorganic layers, currently offer the best resistance to oxygen and water ingression. However, the complexity of the multilayer structure makes the deposition costly and time-consuming. Here we report an effective singlecompound barrier layer deposited by single-chamber plasma enhanced chemical vapour deposition (PE-CVD) from hexamethyl disiloxane (HMDSO) and oxygen source gases. The barrier layer has displayed excellent permeation resistance, with coated OLED devices surviving over 1000 hours in accelerated shelf-life tests (65°C and 85% relative humidity) in near perfect condition. Material characterisation detailed in this paper indicates that the material is an inorganic-polymer hybrid, combining the permeation resistance of an oxide with the flexibility of a polymer. The surface characteristics, chemical composition and mechanical properties of the novel barrier material are investigated with variation in PE-CVD deposition conditions. INTRODUCTION Due to the potential performance enhancements over other flat-panel display technologies and their inherent flexibility, organic light emitting diodes (OLEDs) have become the object of increasing development in recent years [1]. OLEDs, as with other organic electronics, suffer rapid degradation on exposure to water or oxygen. Degradation is observed as non-emissive dark spots on the light-emitting surface [2]. As a result, without suitable encapsulation, device lifetimes are extremely limited. The required water vapour transmission rate (WVTR) for an OLED lifetime of >10 000h is commonly quoted as 1 x 10-6 g/m2/day [3]. Required oxygen transmission rates (OTR) for similar lifetimes are reported as anywhere in the range from 10-5 to 10-3 cm3/m2/day [3]. These permeation rates are orders of magnitude below the requirement of other flat panel display technologies [3], whilst the best single-layer food packaging materials only achieve a WVTR over 4 orders of magnitude higher than this requirement [4]. In rigid displays these low permeation requirements can be answered by encapsulation between glass plates, with wide and thin epoxy seals. But the fabrication of flexible OLED provides a new challenge. A barrier layer for flexible applications must combine very low water and oxygen permeation with mechanical flexibility, whilst having a deposition process compatible with the OLEDs, i.e. a low (ambient) temperature.
In principle, inorganic barrier materials such as SiO2, SiNx or Al2O3, are impermeable to water and oxygen [3]. However, research has shown tha
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