Electrical calcium test for moisture barrier evaluation for organic devices.

We discuss the electrical calcium test--a method to measure very small rates of water vapor permeation through barrier films with high throughput. The sensitivity range for our design is found to be 10(-5) to 15 g/(m(2) d). Moreover, a closer look at the importance of electrodes series resistance is taken: We show that permeation rates are underestimated if it is neglected. Taking this series resistance and Fickian diffusion into account not only the steady, but also the transient state of the permeation curve can be fitted. Using this approach, permeation barriers with different permeabilities are evaluated leading to water vapor transmission rates well comparable to coulometric measurements. The calcium layer morphology is investigated by atomic force microscopy measurements indicating microscopical inhomogeneities during degradation. Variations of electrode material and calcium layer thickness are carried out to examine their influence on the measured permeation. Additionally, optical and electrical calcium tests are compared. Small differences in the time dependence are observed and discussed.