Influence of deposition temperature on microstructure and gas-barrier properties of Al2O3 prepared by plasma-enhanced atomic layer deposition on a polycarbonate substrate

Abstract

We prepared polymer-based encapsulation films by plasma-enhanced atomic layer deposition (PEALD) of Al₂O₃ film on a polycarbonate (PC) substrate at 80–160 °C to fabricate Al₂O₃/PC barrier films. The thermal and dynamic mechanical properties of the PC substrate, the structural evolution of PEALD Al₂O₃ films, the optical transmission, surface morphology, and gas-barrier properties of Al₂O₃/PC film are all studied in this work as a function of temperature. The glass transition temperature T_g of the PC substrate is about 140 °C, and the coefficient of thermal expansion increases significantly when the temperature exceeds T_g. Increasing the deposition temperature from 80 to 160 °C for Al₂O₃ film deposited over 300 cycles increases the density from 3.24 to 3.45 g cm⁻³, decreases the thickness from 44 to 40 nm, and decreases the O/Al content ratio from 1.525 to 1.406. Al₂O₃/PC films deposited at 80–120 °C have no surface cracks, whereas surface cracks appear in samples deposited near or above 140 °C. Upon increasing the deposition temperature, the water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) of Al₂O₃/PC films decrease significantly at temperatures below T_g, and then increase at temperatures near to or above T_g due to cracks in the films. The optimal deposition temperature is 120 °C, and the minimum WVTR and OTR of Al₂O₃/PC film are 0.00132 g per (m² 24 h) and 0.11 cm³ per (m² 24 h 0.1 MPa), respectively. The gas-barrier properties of the Al₂O₃/PC films are attributed to both the densification of the Al₂O₃ film and the cracks, which are caused by the shrinkage of the PC substrate.