Study of mechanical degradation of freestanding ALD Al 2 O 3 by a hygrothermal environment and a facile protective method for environmentally stable Al 2 O 3 : toward highly reliable wearable OLEDs.

Al 2 O 3 deposited via atomic layer deposition (ALD) has been used as an insulating and barrier film for thin-film transistors, organic electronics, and microelectromechanical systems. However, ALD Al 2 O 3 films are easily degraded by hydrolysis under harsh hygrothermal conditions, owing to their poor environmental stability. In this study, the mechanical properties and water-vapor transmission rate (WVTR) of environmentally degraded Al 2 O 3 films were investigated by varying the temperature and relative humidity (RH). The hygrothermal environment led to surface and pinhole-concentrated degradation based on aluminum hydroxide, which caused an increased WVTR and reduced elongation of the films in harsher environments. In particular, the elongation of the degraded Al 2 O 3 films was reduced to 0.3%, which is one-third of that of as-deposited Al 2 O 3 , and their WVTR increased on the order of 10 -1 g m -2 day -1 , which is more than 1000 times that of as-deposited Al 2 O 3 . Therefore, we introduced a functional silane-based inorganic-organic hybrid layer (silamer) onto the Al 2 O 3 films to improve their environmental stability. The silamer helped preserve the characteristics of Al 2 O 3 films by forming a strong and continuous aluminate phase of Al-O-Si at their interface in hygrothermal environments. Furthermore, the silamer-capped Al 2 O 3 was shown to be an environmentally stable encapsulation for application in wearable organic devices.