Sony Corp developed a 9.9-inch flexible OLED panel and announced it at SID 2012, which took place from June 3 to 8, 2012, in Boston, the US (thesis number: 74.1L).
The pixel count, pixel pitch and resolution of the panel are 960 x 540, 228μm and 111ppi, respectively. Its thickness is 110μm.
Sony employed an amorphous IGZO TFT, which is an oxide semiconductor, as a driver element. The OLED panel realizes color display by using white OLED devices and red, green, blue and white (RGBW) color filters (CFs).
The structure of the OLED device is a top-emission type that extracts light from the side opposite to the TFT board. The panel has a 100% or higher color gamut on NTSC standards.
The OLED panel was made by using two glass substrates to which films are attached. On one substrate, TFTs and OLED devices are formed. On the other substrate, CFs are formed. After attaching the two substrates to each other, the glass substrates are removed. The TFTs, OLED devices and CFs can be formed by using the same manufacturing processes as used for normal glass substrates.
"It is a realistic choice for volume production of a flexible OLED panel," Sony said.
For the amorphous IGZO TFT, Sony employed a common process that uses vacuum film forming and photolithography technologies. The IGZO layer and gate dielectric film (SiOx) are formed by sputtering and PECVD (plasma-enhanced chemical-vapor deposition), respectively.
It has a bottom gate-type TFT structure, and an etch stop layer is formed on the upper part of the semiconductor layer to improve reliability. Its carrier mobility and subthreshold swing are 13.4cm2/Vs and 0.2V/dec, respectively.
"They are the same as in the case where the TFTs are formed directly on a glass substrate," Sony said.
The characteristics of the TFTs did not change when the glass was removed, it said.
The white OLED devices are formed by using low-molecular materials and a vapor deposition technology. Commenting on the reason why Sony employed the top-emission structure, it said, "We wanted to make use of our technologies and know-how developed for OLED TVs, OLED monitors, head-mounted displays and so forth." The CFs were formed with a common photolithography technology. The process temperature is 100°C or lower.
Sony did not exhibit the OLED panel at the SID but showed it on a PC screen.
"We have just made the panel and did not have time to evaluate its reliability for bringing it out," the company said.