Moisture Barriers for Flexible Electronics

Defects on plastic substrates such as pinholes, cracks and grain boundaries cause a 'pore effect', where oxygen and water molecules are able to seep through and penetrate through the plastic barrier and into the active material. For applications such as flexible OLED displays, organic solar cells, or even electrophoretic displays, sensitivity to oxygen and moisture compromises device lifetime significantly. This means that in order to achieve adequate lifetime for flexible devices that would make viable commercial products, the pathway for oxygen and moisture down into the active layers must be blocked.

Tera-Barrier Films is a portfolio company of Exploit Technologies Pte. Ltd. (ETPL), the commercialisation arm of Singapore's Agency for Science, Technology and Research (A*STAR) and Applied Ventures, LLC, the venture capital arm of Applied Materials, Inc. as of August 2009. The company was incubated by Exploit-Technologies Pte. Ltd. as a Flagship programme for two years prior to spin-off.

Current barrier technologies focus on reducing these defects by using alternate organic and inorganic multilayers coated on plastic. In contrast, Tera-Barrier has taken an innovative approach to resolve the 'pore effect' by literally plugging the defects in the barrier oxide films using nanoparticles. This reduces the number of barrier layers needed in the construction of the barrier film down to two layers in this unique nanoengineered barrier stack. Tera-Barrier's barrier stack consists of barrier oxide layers and nanoparticulate sealing layers. The nanoparticles used in the barrier film have a dual function - not only sealing the defect but also actively reacting with and retaining the moisture and oxygen.

The result is a moisture barrier performance of better than 10-6 g/m2.day which satisfies even the most stringent requirements for flexible organic device substrates. The barrier film also has a lag time of more than 2,300 hours at 60 ⁰C and 90% RH (i.e. the time required for moisture to pass through the barrier film under those conditions).

It's also important to point out that the barrier layer on its own is not an adequate way to keep oxygen and moisture away from the active materials. Moisture ingress can also occur from the side of the device if it is not adequately sealed. This leads to specific requirements in water vapour transmission rates for the sealants used in electronic devices.

Two of the main companies developing these types of adhesives are Henkel and DELO, Henkel focused mainly on thermally-cured solutions while DELO is focused on UV-cured adhesives.

A trade-off becomes apparent when trying to find the right balance of permeation rates and flexibility. The adhesives that are characterised by the best performance in terms of water vapour transmission are more rigid and would compromise the overall flexibility of the final device. This means that in order to manufacture devices of a given flexibility, permeation performance needs to be sacrificed. Hence, a lot of research and development effort is focused into the development of systems that would lead to a good balance between permeation performance and flexibility.

For more in-depth presentations from Henkel, DELO and Terra Barrier as well as breakthroughs in other materials, manufacturing and novel devices, don't miss the opportunity to attend Printed Electronics/Photovoltaics Europe, in Dusseldorf, Germany on the 5th and 6th of April 2011.

For more information, visit the website www.idtechex.com/dusseldorf