Analysis of Nanoporosity in Moisture Permeation Barrier Layers by Electrochemical Impedance Spectroscopy

Abstract

Water permeation in inorganic moisture permeation barriers occurs through macroscale defects/pinholes and nanopores, the latter with size approaching the water kinetic diameter (0.27 nm). Both permeation paths can be identified by the calcium test, i.e., a time-consuming and expensive optical method for determining the water vapor transmission rate (WVTR) through barrier layers. Recently, we have shown that ellipsometric porosimetry (i.e., a combination of spectroscopic ellipsometry and isothermal adsorption studies) is a valid method to classify and quantify the nanoporosity and correlate it with the WVTR values. Nevertheless, no information is obtained about the macroscale defects or the kinetics of water permeation through the barrier, both essential in assessing the quality of the barrier layer. In this study, electrochemical impedance spectroscopy (EIS) is shown as a sensitive and versatile method to obtain information on nanoporosity and macroscale defects, water permeation, and diffusivity of moisture barrier layers, complementing the barrier property characterization obtained by means of EP and calcium test. EIS is performed on thin SiO2 barrier layers deposited by plasma enhanced-CVD. It allows the determination of the relative water uptake in the SiO2 layers, found to be in agreement with the nanoporosity content inferred by EP. Furthermore, the kinetics of water permeation is followed by EIS, and the diffusivity (D) is determined and found to be in accordance with literature values. Moreover, differently from EP, EIS data are shown to be sensitive to the presence of local macrodefects, correlated with the barrier failure during the calcium test.

Control of the intrinsic microstructure in AP-PECVD synthesised amorphous silica thin films

“…Ellipsometric porosimetry (EP) and electrical impedance spectroscopy (EIS) were two alternative techniques used extensively by Perrotta et al to very effectively characterise the nano-porosity, the pore size range and the presence of macroscale defects in the structure of silica layers. [28][29][30][31] Due to the nature of these techniques, however, the majority of the analysis was performed on samples deposited upon rigid silicon wafers, rather than exible polymer substrates. A full characterisation of the nano-pore content of silica layers was unfortunately found to be problematic using EP if a polyethylene terephthalate substrate was used.…”

Research on flexible display at Ulsan National Institute of Science and Technology

“…Therefore, thin-film encapsulation (TFE) with soft materials has been investigated for flexible encapsulation but the TFE techniques result in an low barrier to permeation, compared with other rigid encapsulations with higher-density barrier films. Some researchers have suggested stacked multi-layered TFE with heterogeneous thin films 54,55 and special patterning techniques to increase the penetration path length of gas molecules. 56 Stacks of polymers and metal oxide nano-materials or carbon materials have thus been studied for flexible TFEs.…”

Encapsulated perovskite based photovoltaics devices with high stability

“…Additional measures are needed to reduce the exposure to the moisture from the perovskite film. [9,10] The metal oxide barrier layer can be deposited using different methods, such as electron-beam deposition (ED), plasma enhanced−chemical vapor deposition (PE-CVD) [10] and atomic layer deposition (ALD). Moisture that has permeated through the epoxy sealing can be absorbed during long-term operation.…”