Ellipsometric Porosimetry and Electrochemical Impedance Spectroscopy Characterization for Moisture Permeation Barrier Layers

In this work the combination of ellipsometric porosimetry (EP) and electrochemical impedance spectroscopy (EIS) is extensively addressed in order to characterize the nano-porosity and further elucidate its influence on the water permeation properties of plasma enhanced-CVD SiO2 layers. Pores with diameter in the range of 0.27-0.6 nm are studied by adopting a multi-solvent/multi-ion approach, with EP and EIS, respectively. This combined study has brought to conclude that open pores larger than 0.42 nm are responsible for WVTR values in the range of 10^-3-10^-5 gm^-2 day^-1, while pores with diameter between 0.42-0.27 nm were found to drive the transition to excellent moisture barrier layers (10^-6 gm^-2 day^-1). Moreover, it is shown that EIS is capable of detecting macro-scale defects, next to nano-porosity, being thus a powerful tool for the analysis of moisture barrier layers.