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.