OLED's barrier films and thin film encapsulation: IDTechEx's review: Page 5 of 6

July 25, 2019 //By Julien Happich
barrier film
Flexible and foldable high-performance barrier or encapsulation technology had long represented a technology challenge. The industry spent a decade and a half optimizing the approaches and the processes to achieve large-area production-grade results.

In another development, a special solution processed layer is being developed. This layer can be solution cast to replace the vacuum deposited inorganic layer, thus boosting process time and reducing CapEx investments to make the technology more accessible to a wider range of producers. The layer can be cured at temperatures around 120C (2min) and will require an argon plasma treatment step to improve film quality. This film can withstand high temperatures, thus making it a good option for the bottom barrier on backplane technologies such as LTPS. It can also be used as the top barrier. Here, it could be solution coated on a planarizing organic layer atop the OLED structure. This method has been demonstrated on Gen2.5 substrates, achieving 5E-6 g/sqm/day and passing 200k bending test around a 3mm radius. This technique has already been licensed to two or more firms, seeking to leverage the solution processability to produce low-cost high-performance barrier films.

Many have already reported single-layer barrier results using ALD or PECVD. In using the latter, the chemistry of the inorganic layer can be graded to improve performance. Indeed, promising results exceeding the required WVTR are often reported. However, it is doubtful whether extrinsic WVTR can also be maintained over large areas and the bendability tests passed without the additional organic layer. This is an ongoing area of research. Many are also working on incremental but important improvements such as enhancing organic-to-inorganic adhesion, improving yield, shaving small amounts off the thickness, and so on. In general, with time, the TFE stack will be further simplified and thinned, the TACT time and production step shortened, and yield improved even over larger mother substrate sizes.

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