Critical thickness of permeation barriers made from Ozone-based atomic layer deposited Al2O3 at low temperature

Abstract

Organic light emitting diodes (OLEDs) are easily degraded by water and oxygen in ambient conditions. Therefore, thin film encapsulation is needed for protection of OLEDs. Atomic layer deposition (ALD) has advantages over other methods, such as thickness control, step coverage and low defect density due to self-limiting surface reaction and it is able to deposit at low temperature for OLEDs encapsulation. We investigated critical thickness of Al2O3 films grown by ozone-based ALD at low temperature (100 ℃) as moisture permeation barrier. Electrical Ca test was performed at a temperature of 50 ℃ and at a relative humidity (RH) 50% to derive the water vapor transmission rate (WVTR) of Al2O3 films. As the thickness of Al2O3 thin film increased above 25nm, width of decrease of WVTR decreased significantly. Pinhole is the main moisture permeation path, WVTR depend on number of pinholes. As the thickness of Al2O3 thin film increased, pinhole density decreased and refractive index increased. As a results of experiments, we found that the critical thickness of Al2O3 films grown by ozonebased ALD at low temperature was 25 nm.