Samsung’s Galaxy S4 smartphone is causing excitement, due in part to its many innovative features and applications, such as Air Gesture, Smart Screen, Eye Scrolling, S Voice, Drama Shot, Dual Camera, Story Album, S Health, S Translator, and Group Play, but due also to its impressive specifications. A 2,600 mAh battery, two quad-core processors, a 13 megapixel autofocus camera, 4G LTE network connectivity, temperature, humidity and gesture sensors, and most important, the face of the S4: a 4.99”AMOLED panel with Full HD resolution (1920×1080).
At the end of 2012, we started seeing many Full HD smartphones in development, all using LTPS TFT LCDs. Due to challenges with the evaporation process higher resolutions are generally more difficult for AMOLED. As long as HD (1280 × 720) was the standard smartphone resolution, AMOLED has been able to compete. But with Full HD (1920 × 1080) displays starting to become the new standard for high-end smartphones, AMOLED faces challenges.
Samsung has been using its proprietary Pentile sub-pixel layout to enhance resolution. Samsung’s Galaxy series has benefitted from steady improvements in AMOLED resolution by modifying the Pentile pixel structures.
Table 1 Samsung Galaxy AMOLED Panel Pixel Layouts
Source: AMOLED Process Roadmap Report
So what is the pixel structure of the AMOLED in the S4? Earlier this year, Samsung demonstrated a 4.99” Full HD AMOLED panel, but did not disclose any technical details. We believe that Samsung has revamped its sub-pixel layout to achieve FHD resolution using its existing FMM (Fine Metal Mask) evaporation process. Samsung might be using the advanced s-stripe with hexagonal and diamond-shaped pixels to achieve the higher ppi. According to a previous sub-pixel structure on which Samsung has filed a patent, it is possible that the diamond-shaped sub-pixel structure will be as shown below.
Figure 2 Possible Sub-Pixel Layout of Samsung’s 4.99” FHD AMOLED
The s-stripe arrangement has several advantages. First, the display readability is significantly improved compared to traditional Pentile, which has two sub-pixels per pixel. S-stripe has three sub-pixels per pixel, and an advanced design may have five. The second advantage is that s-stripe may enable longer lifetimes for the display. Normally, the blue organic material has the shortest lifetime; in s-stripe, the blue sub-pixel domain is larger than that of the other colors. This means that the luminance per area can be less for blue, which is less stressful. In this way, the entire OLED display’s lifetime can be extended.
If an s-stripe or advanced version sub-pixel layout is the ultimate solution for AMOLED to achieve 400 ppi+ resolution, then it could be a competitive advantage for Samsung.