All Hot Wire CVD Organic/Inorganic Hybrid Barrier Layers for Thin Film Encapsulation
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All Hot Wire CVD Organic/Inorganic Hybrid Barrier Layers for Thin Film Encapsulation Diederick A. Spee, Merijn R. Schipper, Karine H.M. van der Werf, Jatindra K. Rath, and Ruud E.I. Schropp Nanophotonics – Physics of Devices, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 5, 3508 TA Utrecht, The Netherlands ABSTRACT A water vapor barrier layer is presented that is deposited entirely at temperatures below ~100 C. Our method, using hot wire chemical vapor deposition (HWCVD), is effective in reducing the issue of pinholes in single layers of silicon nitride (SiNx) made at such low substrate temperatures. We succeeded in depositing an all hot-wire simple three-layer structure consisting of two low-temperature SiNx layers with a polymer layer in between, exhibiting a water vapor transmission rate (WVTR) as low as 5*10-6 g/m2/day, determined at a temperature of 60°C and a relative humidity of 90%. This WVTR is low enough for organic and polymer devices. In a second experiment the robustness of the barrier layer is shown with respect to environmental dust. o
INTRODUCTION An important issue for sensitive electronic devices made on flexible plastic substrates, which, contrary to glass, have a high permeability to oxygen and water, is that they can easily be degraded by oxygen and water vapour permeating into their active layers. Many devices, such as organic light emitting diodes (OLEDs), flexible solar cells, especially those on cheap plastics, and rollable displays require permeation barrier layers on flexible substrates and on top of the device[1-3]. Such a barrier can be created by depositing an inorganic/organic multilayer in which the organic layers decouple defects in consecutive inorganic layers, in this way decreasing chances of pinholes propagating through the entire multilayer. To create such a multilayer a combination of SiNx and polymer layers is very suitable [4]. For the polymer layers, we are using poly(glycidyl methacrylate) (PGMA), which is a widely available and inexpensive material. Our SiNx is deposited by HWCVD and the PGMA by initiated chemical vapor deposition (iCVD), a variant of HWCVD where an initiator is dissociated into two radicals at a hot filament and starts the polymerization process [5]. HWCVD and iCVD are very similar techniques and can easily be implemented in a roll-to-roll or inline process, since both use heated wires as a linear source of radicals, which means that when the substrate is moved perpendicularly to the wires the deposition will be homogeneous in both dimensions [6]. Depositing SiNx on PGMA layers, the main requirements that need to be fulfilled are: (i) that the PGMA layers should be very stable against the flux of chemical species during SiNx deposition [7] and (ii) that the SiNx must be deposited at low substrate temperatures, compatible with common plastic substrates and also PGMA. To achieve PGMA layers as stable as possible they were deposited at a wire temperature not exceeding 220ºC. For the deposition of the SiNx a dedicated reactor
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