Internal Sensor Compensation for Increased Ca Test Sensitivity

The development of state-of-the-art barrier films and encapsulation schema for displays and photovoltaics requires precise measurement of water vapor permeation as quickly as possible. We have demonstrated improvements to our electrical, Ca-trace-based water vapor transmission rate measurement technique without introducing any additional cost or sample handling concerns. Most importantly, the contacting scheme was changed so that the effective length of the sensor traces can be more precisely determined making the contact resistance between the Ca and Au/Ti films far less likely to affect the results. A 4-pt contacting pattern was also applied to the internal (non-data) witness trace. This expanded the potential utility of the witness trace from just an indicator for the integrity of the sample assembly, to also being used to compensate for measurement error. Lastly, we increased the relative precision of our resistance measurements by implementing a Ca sensor trace with significantly higher resistance. Principally, these changes produce significant measurement improvements for permeation rates less than 10^-4 g/m²/day, by lowering the noise floor, reducing required measurement time, and increasing the reproducibility of this test method.