Paper TF-MoM5
Nanolaminate Gas Diffusion Barriers on Polymers with Exceptionally Low H₂O Permeabilities

Monday, October 15, 2007, 9:20 am, Room 613/614

Flexible, ultrathin gas diffusion barriers are required for the protection of organic electronics, e.g. organic light emitting diodes (OLEDs) in flexible displays. Existing barriers provide insufficient protection from permeating H₂O and O₂ gases. Our earlier work demonstrated that a low water vapor transmission rate (WVTR) of ~1 × 10^-3 g/m²/day could be achieved on polyethylene naphthalate (PEN) and Kapton using Al₂O₃ ALD films with thicknesses of ~25 nm. These H2O transmission rates are not low enough to meet OLED requirements. The Al₂O₃ ALD films also degrade over time with exposure to H₂O vapor. To lower the H₂O transmission rates further and to protect the Al₂O₃ ALD films, we have used additional layers in combination with the ~25 nm Al₂O₃ ALD layer. The additional layers were one layer of silicon nitride with a thickness of >60 nm deposited by plasma-enhanced chemical vapor deposition (PE-CVD) or one layer of SiO₂ with a thickness of ~60 nm deposited using rapid SiO₂ ALD. Both of these additional layers in combination with the ~25 nm Al₂O₃ ALD layer reduced the measured WVTR to ~1 × 10^-4 g/m²/day. When deposited on top of the Al₂O₃ ALD film, these silicon-containing layers also protect the Al₂O₃ ALD film from H₂O exposure. Nanolaminates of Al₂O₃ ALD and SiO₂ ALD should further reduce the WVTRs. These nanolaminate films are fabricated by alternating the Al₂O₃ ALD and SiO₂ ALD to create 2 bilayers, 3 bilayers or higher numbers of bilayers. Tests of multiple bilayer nanolaminate structures of Al₂O₃ ALD and SiO₂ ALD on Kapton have yielded extremely low WVTRs of 5 × 10^-5 g/m²/day using the HTO testing technique. These exceptionally low WVTRs are approaching the range that is necessary for OLED devices in flexible displays.