Wednesday, 17 Jul 2019

Holst Centrer develops novel barrier stack for foldable OLED displays

By optimising the design of this stack, Holst Centre's scientists have been able to control its mechanical properties and create a much more flexible barrier

Holst Center - Foldable OLED display with novel barrier layer

15 Nov 2017 | Editor

Researchers from Holst Centre have solved a major challenge in creating large-area displays for portable devices, demonstrating a new protective barrier for organic electronics that is foldable and allows high-temperature processing of display backplanes on top.

According to the Holst Centre’s the researchers new optimised barrier makes foldable displays possible. It comprises an organic layer sandwiched between two layers of silicon nitride (SiN) – a standard barrier layer material.

By optimising the design of this stack, Holst Centre's scientists have been able to control its mechanical properties and create a much more flexible barrier that ensures the neutral stress line during bending is 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.

Crucially, 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.

Moreover, it means the barrier can withstand the high temperatures used in display production processes, making it suitable for the bottom protective layers.

The Holst Center researchers have created OLED demonstrators using the new barrier that 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.

The Holst Centre report that it is currently transferring this latest barrier technology to production at a partner's facility.

"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 optimised 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."

Hylke Akkerman, Program Manager at Holst Centre


About Holst Centre

Holst Centre is an independent R&D center that develops technologies for wireless autonomous sensor technologies and flexible electronics, in an open innovation setting and in dedicated research trajectories. A key feature of Holst Centre is its partnership model with industry and academia based around roadmaps and programs. It is this kind of cross-fertilization that enables Holst Centre to tune its scientific strategy to industrial needs.

Holst Centre's fundamentals are to contribute to answering global societal challenges in healthcare, lifestyle, sustainability and the Internet of Things. This is visible through the motivation of its researchers, its different collaboration models and the choice of its research topics.

Holst Centre was set up in 2005 by imec (Flanders, Belgium) and TNO (The Netherlands) and is supported by local, regional and national governments. Located on High Tech Campus Eindhoven, Holst Centre benefits from, and contributes to, the state-of-the-art on-site facilities. Holst Centre has over 200 employees from some 28 nations and a commitment from more than 50 industrial partners.

Source: Holst Centre

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