Dresden 2014 – scientific programme
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O: Fachverband Oberflächenphysik
O 86: Organic Electronics and Photovoltaics VI (DS jointly with CPP, HL, O)
O 86.5: Talk
Thursday, April 3, 2014, 18:45–19:00, CHE 91
Fracture and corrosion protection for thin-film encapsulation - Fine-tuning the electrical calcium corrosion test for water vapor permeation measurements — •Frederik Nehm, Hannes Klumbies, Lars Müller-Meskamp, and Karl Leo — Institut für Angewandte Photophysik, TU Dresden, Dresden, Deutschland
In recent years, the demand for ultra-high moisture barriers has strongly increased due to the ongoing development of organic electronics. Thus, the ability to measure water vapor transmission rates (WVTRs) below 10−5 g(H2O)/m2d - less than a monolayer in 10 days - is crucial for barrier development. The electrical calcium corrosion test - monitoring the decreasing conductivity of a thin calcium film turning into calcium hydroxide - is a sensitive, cost-efficient method to measure such low WVTRs. However, poor design can cause a high background rate or test breakdown. We show that calcium corrosion causes barrier breaking by both expansion and hydrogen emission. As a countermeasure, we introduce organic (C60) buffer layers for decoupling on both sides of the calcium film. Further investigations show elevated calcium corrosion at the calcium-electrode-interface which can be prevented by a proper choice of the electrode material. Finally, the massive corrosion of barrier thin films is shown to be prevented by glueing a polymer foil onto the barrier under testing. With these precautions, we show atomic layer deposited alumina barriers measured in thin film encapsulation structure close to an actual device architecture. At 30∘C, 90% rh, WVTRs of below 5· 10−5 g(H2O)/m2d were obtained.