The new barrier layer could help with the design of large-area foldable OLED-based displays for portable electronics.
The flexible moisture-proof protective barrier consists of an organic layer sandwiched between two layers of silicon nitride (SiN). The stack design's mechanical properties were optimized for flexibility, with demonstrators achieving a bending radius of 0.5mm. The new protective barrier ensures that the neutral stress line during bending stays close to the active layers of the display to prevent mechanical and electrical degradation. The organic material also helps prevent moisture penetration through pinholes by ensuring very slow lateral spreading of water between the SiN layers. What's more, the particular organic material used is stable up to 400°C and can be applied by slot-die coating. This allows the SiN layers to be deposited at 350°C, improving their quality and ability to prevent water penetration. It also means the barrier can withstand the high temperatures used in display production processes, making it suitable for the bottom protective layers.
“Foldable displays are a hot topic right now, with many people claiming to demonstrate them. But the term is applied quite loosely, and very few – if any – of these demonstrators achieve the bending radii of 2mm or less needed to be truly foldable. Our optimized multilayer barrier now makes foldable OLED displays possible. Not only does it enable very small bending radii, it is compatible with standard display production processes and provides excellent protection against water and stress for long-lasting displays,” said Hylke Akkerman, Program Manager at Holst Centre.
OLED demonstrators using the new barrier have achieved 1000 hours with no blackspots in accelerated lifetime testing, even after ten thousand cycles of folding with a bending radius of 0.5mm. This represents an operational lifetime of several years. With earlier versions of the barrier already deployed in its own Gen 1 pilot production line, Holst Centre is currently transferring this latest barrier to a production at a partner’s facility.