TOKYO Using research out of Yamagata University, two groups in Japan are developing plastic substrates that could be used as the basis of flexible organic light emitting displays (OLEDs).
Nagase Inteco Inc. (Nara, Japan) has worked with an undisclosed company to develop a 2-inch white OLED prototype that features a plastic film covered with an inorganic barrier layer. Separately, Dai Nippon Printing Co. Ltd. has taken the transparent "barrier film" commonly used in plastic food storage bags to create an OLED substrate. Both companies' work is based on research led by Junji Kido, associate professor at the Graduate School of Science and Engineering of Yamagata University. Kido worked jointly with Nagase and its silent partner, and directed Dai Nippon Printing's research as well.
The Nagase group's white OLED features a plastic substrate coated with silicon nitrogen oxide. The company intends to promote the display as the light source for LCD backlights and other applications. "It is difficult for a plastic to work as a full barrier, so we put a barrier layer on it," said Kido. Red, blue and green fluorescent pigments are doped in a PVK polymer to form the emitting layer that generates white light
The panel is driven at 6 to 10 volts and has emitting efficiency of 2 lumen per watt, high for white EL displays, Kido said. "Using small-molecule materials, the emitting efficiency has reached to 15 lumen per watt, and we have an outlook to double that efficiency," he said.
Companies that use the flexible substrate will be able to develop various types of displays, including dot-matrix, said Kido.
Nagase intends to offer samples of the plastic substrate this autumn and to start production at the same time, at a capacity of 600,000 units of 2-inch panels a month.
Dai Nippon Printing, a prominent Japanese printing company, used printing technology to developed the multicolor luminous layer for its prototype. The company said the printing of polymer EL materials on a plastic film could lead to large-sized, low-cost flexible displays.
The barrier layer in the Dai Nippon Printing prototype uses an improved version of the barrier film developed in 1997 now common in plastic bags. The improved film sandwiches the EL layer, buffer layer, polymer organic EL layer and cathode layer to protect from moisture and oxygen.
On a 150 x 150-mm substrate, Dai Nippon researchers formed a 110 x 90-mm display area consisting of red and green printed areas. The display is 0.25 mm thick. The researchers have already established a technology to print red, green and blue emitting materials in 100-micron intervals, a company spokeswoman said.
The company is not settled on EL materials, and is looking to find better performing materials through a possible purchase or partnership. It plans to commercialize the display by 2003.
Dai Nippon Printing hasn't decided on its OLED business plan, either. It may offer the display itself, the substrate or its printing technology, the company spokeswoman said.