In OLED manufacturing, inkjet printing (inkjet) creates patterned films without using a mask, which clearly differentiates it from mask-dependent techniques like evaporation.
The resulting benefits include lower production costs, fewer defects, manufacturing flexibility, and scalability to large-size panels. These combined advantages make inkjet ideal for OLED mass production.
Materials usage is typically the largest CoO component in OLED manufacturing. With inkjet, virtually all of the deposited material forms the finished film. This means there is almost no waste. Mask-dependent approaches, on the other hand, deposit much of the material on the chamber walls or the mask.
Inkjet improves CoO by eliminating the cost of manufacturing, cleaning and replacing masks. Uptime is also higher because there are no production interruptions to clean the chamber walls. Finally, with no superfluous material on the masks or chamber walls to flake off and contaminate the panel surface, defects are dramatically lower.
Inkjet provides flexible manufacturing for display producers, which enables quick turn-around on customer requests, and ultimately, faster time to market. If a display with a new shape is required in R&D or production, it involves a simple recipe change on an inkjet printer which can be done very quickly. With a system that uses a mask to define the shape, however, a new mask must be designed, tested, and manufactured for every new display shape, which is costly and time consuming. Inkjet’s inherent flexibility saves valuable time during all phases of the product cycle, from R&D to mass production.
Scaling up to larger glass sizes is critical to realizing the full economic potential of OLED displays, especially for mid- and- large-size OLED devices (e.g., TVs). Inkjet is a scanning system, where the film is deposited by making multiple scans over the glass. Scanning systems are inherently scalable to larger glass sizes—to a first order, more scans are added to cover more area. Systems that process the full area of the glass in a single process are not so easy to scale up. Evaporators, for example, have been unable to successfully scale up to Gen 8 or larger due to issues scaling the fine metal mask.
OLED devices are extremely sensitive to trace levels of oxygen and moisture. Protection from these elements during operation is imperative. For flexible devices, thin film encapsulation using inorganic/organic multilayers has become the integration scheme of choice. The advantages discussed above have made inkjet the approach of choice for deposition of the organic layer of the TFE stack. The material efficiency, higher uptime, and superior defect performance were key considerations in the selection of inkjet for mass production of flexible OLED displays. In addition, inkjet provides more flexibility in the choice of material for the organic film, and the use of a liquid ink provides for better planarization of underlying particles and surface topology—a critical factor in TFE quality.
Currently, RGB OLED is only commercially available for smaller-sized devices such as watches and smartphones. And although consumer demand for larger-scale OLED products, like TVs, is on the rise, pixel patterning by evaporation is not scalable to the large glass sizes required for cost-effective mass production. Inkjet is widely considered the most promising approach for enabling pixel patterning for large-size RGB, mainly due to its inherent scalability to larger glass sizes. In fact, pilot inkjet systems are now in the field for the RGB pixel patterning application.
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