Cathode encapsulation of organic light emitting diodes by atomic layer deposited Al2O3 films and Al2O3/a-SiNx:H stacks

Al2O3 thin films synthesized by plasma-enhanced atomic layer deposition (ALD) at room temperature (25 degrees C) have been tested as water vapor permeation barriers for organic light emitting diode devices. Silicon nitride films (a-SiNx:H) deposited by plasma-enhanced chemical vapor deposition served as reference and were used to develop Al2O3/a-SiNx:H stacks. On the basis of Ca test measurements, a very low intrinsic water vapor transmission rate of <= 2 x 10(-6) gm(-2) day(-1) and 4 x 10(-6) gm(-2) day(-1) (20 degrees C/50% relative humidity) were found for 20-40nm Al2O3 and 300 nm a-SiNx: H films, respectively. The cathode particle coverage was a factor of 4 better for the Al2O3 films compared to the a-SiNx:H films and an average of 0.12 defects per cm(2) was obtained for a stack consisting of three barrier layers (Al2O3/a-SiNx:H/Al2O3). (C) 2012 American Vacuum Society. [DOI: 10.1116/1.3664762]