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¿°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¿×¿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: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 cm2 was obtained for a stack consisting of three barrier layers (Al2O3/a-SiNx:H/Al2O3)