Water Vapor Permeation Testing Of Ultra-Barriers: Limitations Of Current Methods And Advancements Resulting In Increased Sensitivity

Advancements in barrier quality of certain materials have pushed the sensitivity limits of commercially available water vapor permeation equipment. In order for products such as OLED’s which incorporate these high barrier materials, to be viable, current permeation testing methods must be enhanced or altered. In designing a more sensitive method, the limitations of the current methods were first studied. From there, enhancements and modifications to the traditional comparative or concentration sensor produced an order of magnitude increase in sensitivity (from 5x10^(-3) to 5x10^(-4) g/m^2/day.) Permeation results illustrating the new system will be presented as the highlight of the paper. Limitations found in the current methods, alterations made to a traditional system and insight into future modifications that will increase the sensitivity even further will also be included.

A major hurdle for the introduction of flexible OLED’s into the commercial market is the limited lifetime of the devices due primarily to the degradation in the presence of moisture and oxygen. Permeation barriers are required to minimize the exposure of the devices to the moisture and oxygen in the atmosphere. A water vapor transmission rate (WVTR) value of 1 x 10^(-6) g/m2/day has become the unofficial standard for the OLED industry to achieve a device lifetime of >10,000 hours. This value was originally estimated by calculating the amount of oxygen and water needed to degrade the reactive cathode. Obviously an impediment is the development of these barrier materials, however, a concurrent problem is a WVTR method to measure these materials as they are developed.