OLED's barrier films and thin film encapsulation: IDTechEx's review: Page 4 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.

Future trends of TFE technology

There are trends to further evolve TFE technology too. Atomic layer deposition (ALD) is proposed as a superior deposition technology over PECVD. ALD does produce high-quality films at a lower thinness although the low thinness can limit extrinsic performance despite high intrinsic barrier values. However, temporal ALD is ill-suited to large-area deposition given its low deposition rates. Spatial ALD does improve the productivity however it is still an immature technology that has been mainly demonstrated on narrow-web films or on small-sized silicon wafers. Companies had attempted to also implement s-ALD on large-sized glass substrate however none were yet production-qualified. The developments on ALD will however continue, especially as PECVD replacement, since a key driver is to continually narrow down the TFE structure without performance compromise.

In another development, an all-PECVD process is being developed with a potential for a single-chamber deposition. Here, the structure is composed of an inorganic layer (e.g., SiNx), a buffer adhesion layer (e.g., SiONx) an organic layer, and a stress reduction layer (e.g., SiONx). The organic layer is fluorinated plasma-polymerized hexamethyldisiloxane (pp-HMDSO:F) which is plasma deposited through a mask. Significant knowhow exists in processing the pp-HMDSO:F without causing spraying, premature reactions, and other technical issues. There are however issues to resolve such as: cleaning the mask, boosting material utilization, fine-tuning the chemistry, etc. Note that the role of the stress reduction layer is to have a layer with a built-in tensile strength to counteract the compressive stress of the underlying layer, thus helping reliability and optical transparency. The approach has been demonstrated using Gen-4.5 tools, achieving promising results including 200k cycle test around a 2.5R radius. Furthermore, this approach reduces the thickness of the organic layer to 1-2um, a significant improvement in the thickness levels achieved by the incumbent inkjet-printed organics.

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