Many announcements about flexible OLED displays were made at SID 2013. Some companies began to improve the resolutions of their displays to, for example, full HD (1,920 x 1,080 pixels), and increase their sizes. Also, the InGaZnO (IGZO) TFT was employed for all the panels announced this time.
Panasonic Corp developed a 4-inch full-color flexible OLED display (lecture number 18.4L). Its device structure is a top-emission type, and it is driven by amorphous IGZO (a-IGZO) TFTs. It has a pixel count of 224 x 224 x RGB (red/green/blue) and a resolution of 80ppi (pixels per inch).
The base material of the display is polyethylene naphthalate (PEN). It can be bent up to a curvature radius of 10mm.
To make the flexible OLED display, a PEN sheet is attached to a glass substrate, and an OLED layer, etc are formed on it. Then, the PEN is mechanically removed from the glass.
"The maximum process temperature is as low as 150°C," Panasonic said.
The company did not show a prototype of the display in the author's interview.
At the International Display Workshops (IDW'12), which took place in December 2012, Panasonic announced a similar technology together with another company. This time, however, Panasonic used a Ti/Au/Ti gate electrode in place of a Ti/Au gate electrode. Ti strengthens the adhesion between the gate electrode and gate dielectric layer, it said.
Toshiba Corp formed a 10.2-inch full-HD (1,920 x 1,200 x RGBW (W: white)) flexible OLED display on a thin, transparent polyimide substrate (lecture number: 70.1L). Its resolution is 223ppi, which is very high for a flexible OLED display.
The device structure of the display is a bottom-emission type. To realize the full-color display, the company applied an RGBW color filter to an OLED layer that emits white light.
Toshiba showed a prototype of the display in the author's interview. Its panel was very thin and light and trembled when wind was generated by a human movement. It was not turned on in the demonstration because there was no compact, portable power source for the display yet, the company said.
Arizona State University, Army Research Laboratory
A research group from Arizona State University and the Army Research Laboratory of the US prototyped a large 14.7-inch flexible OLED display (lecture number: 70.2L). Its pixel count and resolution are 960 x 720 x RGB and 81ppi, respectively.
The group used amorphous Si TFTs in the past but employed the IGZO TFT this time, for the first time. The process temperature is 200°C or lower, it said.
On contrary to Toshiba, the group did not use a color filter and realized the full color display by stacking red, green and blue light-emitting elements on the panel. It employed a rollable PEN substrate. The group did not show the prototype.