Design of organic/inorganic multilayer water vapor barrier thin films deposited via plasma polymerization for encapsulation

Abstract

Plasma-enhanced chemical vapor deposition was used to deposit organic/inorganic encapsulation thin films on polyethylene terephthalate (PET) substrates by controlling the flow rate of oxygen (O2) and hexamethyldisiloxane. The control of gas flow can deposit different film structures such as a network structure of inorganic thin films and linear and cage-like structures of organic thin films, which are stacked on one another to form a multilayer water vapor barrier film. A calcium (Ca) test was established to measure the WVTR of thin films with a measurement limit of 3.05 × 10−3 g/m2/day. Surface profilometry, ultraviolet–visible spectrometry, and radius of curvature are applied to analyze the physical and optical properties. By depositing different monolayer film thicknesses on the PET, the encapsulation capability also varies. The WVTR of 3-pair (sub/buffer (50 nm)/barrier (100 nm)) multilayer thin films is 7.05 × 10–3 g/m2/day, but that of the 6-pair (sub/buffer (25 nm)/barrier (50 nm)) multilayer thin films decreased to less than the limit of the Ca test after the thickness of the monolayer was reduced. In the case of stacking 4-pair (sub/buffer (50 nm)/barrier (100 nm)) multilayer thin films, the single-layer film is too thick to withstand bending with a curvature radius of 24.3 mm, which may cause film cracks and increase its WVTR. After thinning the thickness of the single-layer, the 8-pair (sub/buffer (25 nm)/barrier (50 nm)) stack with the same total thickness withstands a curvature radius of 24.3 mm, and its WVTR also exceeds the limit of the established Ca test.