ABSTRACT
Figure 11.2 Schematic diagram of an AMOLED design adopted by LG Display. Reproduced with permission from Ref. [124]. Copyright 2013, Wiley-VCH.
In this respect, there are currently two competing color patterning designs thus far, as shown in Fig. 11.3. The first one is called red, green, blue (RGB), side-by-side pixel design where each of the three primary color subpixels are placed adjacent to one another with the blue subpixel being 1.5 times as large as the green
and red subpixels. The reason for a larger blue pixel is that state-ofthe-art blue emitter used is a fluorescent type that is not as efficient as the phosphorescent green and red emitters. Note, once again the length of each primary color OLEDs are optimized for maximum forward light output for each color. Here, no color filters are needed, and polarizers are used to minimize ambient reflections. This design is currently being adopted by Samsung Display, as shown in Fig. 11.3a. This approach has the advantage of high efficiency and lower power consumption. However, one major issue is the yield of the fabrication process when the size of the display becomes large. This is primarily because the fine metal mask (FMM) used for pixel patterning becomes heavy after scaling up and are prone to sagging, which leads to shadowing effect and misalignment of the pixels. Further improvement in the fabrication process was made by Samsung Display to utilize a small-mask scanning (SMS) technique for the OLED deposition. This method is a similar to FMM; however, instead of the substrate and the mask being fixed in one position as with the FMM process, the SMS method, the mask is held constant and the substrate moves. As a result, the mask is only as large as the panel and the possibility of sagging is minimized. However, the yield is still not sufficiently high; hence the production cost remains significant. Other alternative OLED pixel patterning techniques are shown in Table 11.1.
