Paper TF-ThP33
High Moisture-Barrier Films using Roll-to-Roll-Plasma CVD grown SiO_x on Room-Temperature ALD treated PEN Substrates

Thursday, November 10, 2016, 6:00 pm, Room Hall D

Flexible electronic devices are expected to extend its commercial applicability for the bendable applications. Barrier coating depositions on plastic substrates, such as, polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), are essential, because water vapor passes through the plastic films, which might degenerate the performance of electronics devices. It is also essential to enhance the productivity of the barrier coating while minimizing its process costs, where the roll-to-roll process is expected to be a candidate. So far, the roll-to-roll type plasma enhanced chemical vapor deposition (PECVD) system for the SiO_x coating was developed where its barrier ability of water vapor transmission rate (WVTR), was at as low as 5×10^-4 g/m²/day with the 500 nm thick coating on PEN [1]. However, further improvement of WVTR down to below 10^-6 g/m²/day is still demanded for organic light emitting diodes (OLEDs) .

In this study, the SiO_x coating is deposited by the roll-to-roll PECVD, combined with room temperature atomic layer deposition (ALD) of AlO_x to form a stacked structure on the PEN substrate. The SiO_x coating was processed by a PECVD roll coating system (Kobe Steel, Ltd., W35-350CS), where hexamethyldisiloxane (HMDSO) was used as precursor mixed with oxygen. The ALD of AlO_x was performed using trimethylaluminum (TMA) and remote-plasma-exited water vapor, where the plasma was generated with a mixture of water vapor and argon by an induction coil with a frequency of 13.56 MHz [2]. In order to simplify the whole process, the single ALD layer was inserted for the barrier film formation. The stacked structure consisting of CVD-SiO_x/ALD-AlO_x/PEN substrates was used for the experiment. The barrier performance was measured by Aquatran^TM produced by MOCON Inc. with a temperature of 40 °C and a relative humidity of 90 %.

The stacked structure of 300 nm thick CVD-SiO_x on 10 nm thick ALD-AlO_x exhibited the WVTR below 5×10^-4 g/m²/day (This is the detection limit of Aquatran^TM), whereas the film with a single layer of 300 nm thick CVD-SiO_x deposited directly on PEN had a WVTR of 3.38×10^-3 g/m²/day. As a view point of productivity, it is notable that the thin inserting ALD layer drastically effects on the barrier performance. We consider that the present layer-stacking approach is used for the high moisture-barrier films since this technique goes well with the roll-to-roll production.

[1] T. Okimoto et al., The 21th International Display Workshops Proceedings (2014) 1448-1451.