According to Korean media outlet The Elec, Samsung has set a goal of using transparent PI substrates in its foldable phones by 2024, replacing the yellow PI substrates currently in use, with the ultimate goal of allowing the under-screen camera to take sharper photos.
According to industry sources, Samsung Display has set a target of applying transparent polyimide (PI) substrates to foldable phones released around 2024, with the flexible organic light-emitting diodes (OLEDs) currently used in mass-produced foldable phones using yellow PI substrates, the report said.
The reason Samsung Display plans to use transparent PI substrates for flexible OLEDs is to improve the light transmission of the under-screen camera (UPC), whose lens aperture is only visible when using the camera function and is structurally located below the OLED display. When using the camera function of the UPC, external light must pass through the flexible OLED.
Samsung Display has reduced the pixel density of the UPC area to 187 PPI, half the 374 PPI (pixels per inch) of the rest of the display area, to compensate for these drawbacks associated with the first application of UPC to the Samsung Galaxy Z Fold3. If the pixel density is low, it is possible to increase the area that can receive light. However, the size of the display pixels in the UPC area also increases to four times the size of the remaining area, so there is a clear border between the UPC and the rest of the display.
If the Samsung display replaces the yellow PI substrate with a transparent PI substrate as planned, the light transmission in the UPC area will be increased, allowing clearer pictures to be taken than at present. Pixels could also be arranged more densely than they are now, and the borders with the rest of the display would be less visible.
The report also says that the heat resistance and high cost of the transparent PI varnish needed to produce the transparent PI substrate is a challenge. Samsung Display initially wanted to use transparent PI substrates for the Galaxy Z Fold 3, which was released last year, but the application was delayed due to the nature of the transparent PI varnish. If Samsung Display succeeds in developing a transparent PI substrate, it is expected to be used first in Samsung Electronics’ foldable phone OLED and then in Apple’s iPhone.
LG Display is also developing transparent PI substrates for UPC applications based on its own technology roadmap, and the yellow PI substrates are also used in LG Display’s iPhone flexible OLED panels for Apple. According to the roadmap, LG Display plans to increase the light transmission rate of UPC to 20% by 2023 and 40% after 2024.
