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

AlO deposited atomic layer deposition (ALD) has been used as an insulating and barrier film for thin-film transistors, organic electronics, and microelectromechanical systems. However, ALD AlO 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 AlO 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 AlO films was reduced to 0.3%, which is one-third of that of as-deposited AlO, and their WVTR increased on the order of 10 g m day, which is more than 1000 times that of as-deposited AlO. Therefore, we introduced a functional silane-based inorganic-organic hybrid layer (silamer) onto the AlO films to improve their environmental stability. The silamer helped preserve the characteristics of AlO films by forming a strong and continuous aluminate phase of Al-O-Si at their interface in hygrothermal environments. Furthermore, the silamer-capped AlO was shown to be an environmentally stable encapsulation for application in wearable organic devices.