The role of carrier gas flow in roll-to-roll AP-PECVD synthesized silica moisture barrier films

Moisture barrier films are deposited on a polymer foil by roll-to-roll Atmospheric Pressure Plasma Enhanced CVD reactor using a N2, O2, TEOS gas mixture. The film microstructure and permeation properties are studied as a function of the carrier gas flow rate with both static and dynamic film transport. The microstructure is analyzed by spatially resolved attenuated total reflectance (ATR)-FTIR and correlated with the vertical density gradient obtained in the dynamic films and the moisture barrier performance. It is shown that by varying the carrier gas flow rate the vertical density gradient, or the network porosity, can be tuned by governing the convective transport inside the reactor consequently densifying the inorganic film at fixed energy cost (i.e. Yasuda parameter) of the process. Moreover, adopting the bilayer architecture allows to achieve the same moisture barrier properties of 2 · 10−3 g·m−2·day−1 (40 °C, 90% RH) at only half the film thickness of a single layer barrier films, which consequently leads to a throughput increase of almost two times.