OLEDs are attractive for future displays owing to their superior properties including high transparency and flexibility and low power consumption, which are not achieved when using conventional liquid crystal displays. However, the organic materials used as the self-emitting component in OLED displays are highly sensitive to water due to the reaction of organic molecules with intruding water, thus worsening the light-emitting properties. Thus, encapsulation that can effectively block moisture is necessary for OLED displays.
Moisture penetration through encapsulation is due mainly to the defects in the films because moisture permeation is driven by these defects. Therefore, depositing a thin film with small defect density is highly required to develop an excellent moisture barrier for OLED encapsulation.
ALD offers various advantages for an encapsulation layer, such as large-area uniformity, pinhole-free thin film formation, and low deposition temperature. Furthermore, void defect formation on the encapsulation layer, which causes critical degradation of water vapor transmission rates (WVTR), is avoidable owing to the surface self-saturated reaction mechanism of ALD. Moreover, ALD can ensure a low-defect density, resulting in low moisture permeation.