Self-assembled monolayers as a defect sealant of Al₂O₃ barrier layers grown by atomic layer deposition

Self-assembled monolayers (SAMs) were applied to seal defects present in Al₂O₃ barrier layers fabricated on PEN substrate by plasma enhanced atomic layer deposition (PE-ALD), and the effects of the SAM in enhancing the barrier properties were studied. Pinhole defects of Al₂O₃ single layers were covered by SAM based on a 1-dodecanethiol (DDT) precursor. To investigate the formation of SAMs on Al₂O₃ layers, contact angle measurements and field–emission–transmission electron microscopy (FE-TEM) were employed. We found that the barrier properties of Al₂O₃ with SAM were significantly improved compared to those of Al₂O₃ single layers. The SAM/Al₂O₃/Ag/PEN multilayer structure showed a superior water vapor transmission rate (WVTR) less than 5.0 × 10⁻⁵ g m⁻² day⁻¹ at 38 °C and 100% relative humidity, demonstrating its applicability for flexible displays. Mechanical stability was investigated using U-folding bending test. The WVTR of the SAM/Al₂O₃/Ag/PEN multilayer remained less than 5.0 × 10⁻⁵ g m⁻² day⁻¹ after 25,000-cycles bending test using a 5 mm bending radius.