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Within a 500h test, ALD encapsulated poly-LEDs show approximately half the black spot density of plasma deposited a-SiNx:H (300 nm thick) encapsulated devices. The black spot density is further reduced ifthe a-SiNx:H layer is coupled with an ALD layer and such decrease is accompanied by a massive reduction of the black spot area growth in time. A selection of electroluminescence measurements of encapsulated poly-LEDs point out a very promising application of ALD Al2O3 layers in the field of LED encapsulation and will be interpreted in terms of possible mechanisms related to film growth in multi-layer structures.

Al2O3 thin films synthesized by plasma-enhanced atomic layer deposition(ALD) at room temperature (25 ºC) have been tested as water vapor per-meation barriers for OLED devices. Silicon nitride films (a-SiNx:H)deposited by plasma-enhanced chemical vapor deposition (PE-CVD) servedas reference and were used to develop Al2O3/a-SiNx:H stacks. On the basisof Ca test measurements, a very low intrinsic water vapor transmissionrate (WVTR) of ≤ 2·10-6 g·m-2·day-1 and 4·10-6 g·m-2·day-1 (20 oC/50% relative humidity) were found for 20-40 nm Al2O3 and 300 nm a-SiNx:Hfilms respectively. The cathode particle coverage was a factor four betterfor the Al2O3 films compared to the a-SiNx:H films and an average of 0.12defects per cm2 was obtained for a stack consisting of three barrier layers(Al2O3/ a-SiNx:H/ Al2O3).