Dutch R&D institute Holst Centre and American ultra-thin ceramics supplier ENrG Inc. have created a ceramic-based, large-area flexible OLED. The device, manufactured on the 20-40 µm thick Thin E-Strate® ceramic substrate, reportedly promises a lifetime in excess of 10 years without the formation of blackspots. The ceramic carrier is easy to handle and capable of withstanding the high temperatures used in display backplane manufacturing and standard sintering processes.

The ceramic substrate used for the 12 x 2.5 cm prototype OLED device combines many properties of other flexible OLED carriers. It reportedly offers an intrinsic barrier to protect the sensitive OLED from the environment, as with metal foils or flexible glass, but it is reportedly much easier to handle. Like plastic films, the ceramic offers the potential for semi-transparent devices. Its slight opaqueness actively improves light outcoupling, allowing for higher devices efficiencies. Unlike plastic films, though, the ceramic can withstand temperatures up to 1,000°C. With its intrinsic barrier properties, Thin E-Strate OLEDs reportedly can be fully protected with just the addition of a top barrier–simplifying production compared to plastic-based OLEDs. 

“Our Thin E-Strate ultra-thin ceramic has many plus points over other flexible OLED substrates,” said said Kathy Olenick, technical marketing manager at ENrG Inc. “It is the only flexible substrate that has both intrinsic moisture barrier properties and high-temperature capabilities, in combination with being both robust and smooth enough to fabricate an OLED device on. The prototype device made by Holst Centre shows the benefits Thin E-Strate brings new flexible electronics applications.”

The protection the OLED receives, and hence its potential durability, is typically quantified through its water vapor transmission rate (WVTR). In tests, the Thin E-Strate-based OLED demonstrated a WVTR below 8.5 x 10^-7 g/m²/day. In addition, while most flexible OLEDs require a multi-layer barrier on both sides, the Holst Centre-ENrG device reportedly achieved these values with just the ceramic Thin E-Strate at the bottom and a Holst Centre thin film top encapsulation, directly deposited by plasma enhanced chemical vapor deposition (PECVD) and printing of a few layers, on top of the device.

“A WVTR of less than 10^-6 g/m²/day is widely accepted as a minimum requirement for commercial devices,” said said Hylke Akkerman, senior scientist at Holst Centre. “At this level, it takes over 10 years for deterioration due to moisture to lead to visible black spots. But such a rating is difficult to achieve, and many other flexible OLEDs with single-layer barriers have around 10^-5 g/m²/day or higher (equivalent to a 1-year lifetime or less). Beating the 10^-6 g/m²/day target with such a simple structure shows the excellent protection of Thin E-Strate and Holst Centre’s direct thin film encapsulation stack on top. This approach could help further reduce complexity for flexible OLED production.”

For more information, visit www.holstcentre.com or www.enrg-inc.com.