Surface modification of polymeric substrates to enhance the barrier properties of an Al₂O₃ layer formed by PEALD process

Aluminum oxide (Al₂O₃) layers were deposited on various polymeric substrates by a low frequency plasma-enhanced atomic layer deposition (PEALD) process. Polyethylene naphthalate (PEN), polyethylene terephthalate (PET), and polyethersulfone (PES) were tested as substrates for barrier films. Each substrate has its own characteristics to have influences on the Al₂O₃ layer formation and penetration into the substrate, which greatly affected the barrier properties. Prior to the deposition process, polymeric substrates were pretreated in argon and oxygen plasmas, and surface energy was leveled up due to the formation of polar group. Characterizations of the Al₂O₃ layer by Time of Flight - Secondary Ion Mass Spectrometry (ToF-SIMS) revealed that plasma treatment lowered the level of OH⁻ in Al₂O₃ layer. X-ray photoelectron microscopy (XPS) confirmed that A12p peak of Al₂O₃ layer was shifted to a higher core level by plasma treatment. Density of the layer on the plasma treated surface was greater than that of untreated surface. It was found that plasma treatment of the surface had significant effects on the formation of the Al₂O₃ layer, which much improved the barrier performance. Optical transmittance was little affected by plasma treatment and PEALD process. After oxygen plasma pretreatment, the WVTR of the Al₂O₃ layer deposited on the plasma-treated PEN substrate was around 7.2 × 10⁻⁴ g/m²day, which is significantly lower than that of the untreated substrate.