The role of the gradient film properties in silica moisture barriers synthesized in a roll-to-roll atmospheric pressure plasma enhanced CVD reactor

Silica-like films for moisture barriers were deposited on a polymeric substrate in an Atmospheric Pressure PECVD reactor using a N-2/O-2/TEOS gas mixture. Statically deposited silica films were characterized by spatially resolved ATR FTIR and revealed a clear gradient in the silanol concentration. Silanol is an impurity in the silica network, resulting in pore formation, thus a higher silanol content leads to a decrease in the film density. Hence the spatial non-uniformity in the static profile results in a density gradient in the thickness of web-rolled films. The gradual transition from a lower to a higher density film appeared to be an essential requirement for maintaining the film integrity on the polymer. Hence, the porous layer acts as an adhesion promotion layer for the dense top layer. These optimal layer properties are achieved in a continuous single processing step.