Development of the“ CEE-950” Thin Film Encapsulation Equipment for OLEDs

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Evaporation deposition acrylic film5, 12), vaporization acrylic film4), inkjet acrylic film13) and PECVD SiOC film7) have been developed and evaluated as buffer films. Evaporation deposition acrylic film has been recognized for its planarization effect through the formation of a thick film (1–3 μm)5). However, as the maintenance of the inside of the deposition camber (removal of acrylic film attached on the inner wall and internal components) is difficult and requires a large footprint, it has gradually come into disuse.
The inkjet acrylic film is a recently reported acrylic film deposition method. The inkjet method enables film deposition at a specific location of a device substrate and is expected to make up for the difficulties in evaporation deposition acrylic film13), though its full scale evaluation is in the days ahead. Regarding PECVD SiOC film, when PECVD is used for a barrier film, laminated film can be formed using the same deposition method, and therefore, it is expected to simplify system composition and facilitate process operations. SiOC film is formed using a mix of siloxane-based gas (hexamethyldisiloxane, etc.) and oxygen.
The presence of carbon or hydrocarbon inside the SiOx-based film creates an inorganic film having organic features and provides a planarization effect through the formation of a thick film, and for this reason, SiOC film is expected to function as a buffer film.
Our company began the development of organic film deposition technology a long time ago, and has sales records of deposition equipment for forming parylene, polyuria and acrylic films. When developing thin film encapsulation technology for OLEDs, we adopted acrylic film deposition using the vaporization method as it is capable of performing low temperature deposition and makes system structure design simple. The acrylic material was chosen by comparing the accumulated data (physical properties, vaporization conditions and curing conditions) on dozens of candidate monomers, the candidates were narrowed down to several types, and then deposition evaluation was performed using the equipment. With equipment technology currently using our original acrylic material and through optimization of processes, the equipment allows deposition of acrylic only on the substrate surface. Accordingly, unlike the equipment for evaporation deposition acrylic film, there is no attachment of the material on the inner wall of the chamber or internal components, making maintenance inside the deposition chamber unnecessary for a long time and the maintenance work itself is easy. Acr ylic film deposition and curing of acrylic are performed on the same stage without moving the substrate. Table 1 shows the film quality when our acrylic material is deposited as a single film. It satisfies the optical properties, stress and other properties required for OLED devices.

Table 1 Evaluation results of acrylic film quality of G4.5 equipment.
Table 1 Evaluation results of acrylic film quality of G4.5 equipment.

A lamination method in which barrier films and buffer films are layered involves sandwiching a buffer film between barrier films over the OLED device, for example, barrier film/buffer film/barrier film (3-layer lamination), or barrier film/buffer film/barrier film/buffer film/barrier film (5-layer lamination). Although encapsulation performance is likely to increase with more layers, an increase in the number of chambers to be used leads to higher equipment costs and process costs. For this reason, thin film encapsulation with only 3 layers of lamination is on the verge of becoming mainstream. In order to meet the required encapsulation performance with fewer laminated layers, it is necessary to enhance the barrier film’s barrier property and the buffer film’s coverage for gaps in the device’s structure and to protect against foreign matter. One might think increasing the per-layer thickness would be a good way to enhance the barrier and coverage properties, but as this method may reduce the bending performance required of a flexible device, it is necessary to satisfy encapsulation performance while keeping each layer of film as thin as possible.
The composition of our company’s thin film encapsulation is the 3-layer SiNx (400 nm)/Acrylic (250 nm)/SiNx (400 nm) lamination mentioned above, which means we are proposing thinner films than other companies. Owing to the higher barrier property (lower moisture permeability) against moisture/oxygen of our SiNx barrier film in comparison with other companies’ SiNx films as well as to the characteristic of our acrylic buffer film of localizing at stepped portions of a device, the encapsulation performance required from OLED devices can be obtained with a small film thickness.

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