FUJIFILM and nano-electronics research institute, imec have developed full-color organic light-emitting diodes (OLED) by using a photoresist technology for organic semiconductors, paving the way to producing high-resolution and large organic Electroluminescent (EL) displays and establishing cost-competitive manufacturing methods. Organic EL displays are increasingly used for televisions, mobile devices as well as wearable devices. Since they can be made thin and flexible, while also offering excellent response time and contrast ratio. It is said that today's products require organic EL displays of high pixel density, i.e. around 200ppi for 4K televisions, 500ppi for full HD mobile devices and even higher density for compact displays for wearable devices. There has been active R&D for organic semiconductors to develop a high-resolution patterning method for organic EL materials to be used in these products.
In 2013, Fujifilm and imec jointly developed photoresist technology for organic semiconductors that enables submicron patterning without damaging the organic semiconductor materials, based on photolithography capable of high-resolution patterning on large substrates.
In the photolithography method, a film is formed by coating photoresist onto the substrate to be processed, and photochemical reaction occurs within the resist film by exposing patterns through the mask. This microfabrication method forms a mask-like resist pattern on the substrate through development, and transfers the resist pattern onto the substrate as protective material for etching.
An existing i-line exposure system can be used for the new technology. This is why the technology has attracted wide attention since the development announcement with anticipation of a cost-effective way of manufacturing high-resolution organic semiconductor devices.
In the latest achievement, Fujifilm and imec produced full-color OLEDs with the photoresist technology for organic semiconductors and successfully verified their performance. Red, green and blue organic EL materials were patterned, each in the subpixel pitch of 20μm, to create full-color OLEDs. Subpixel pitch represents the midpoint distance between two neighboring subpixels.
An OLED array of 40 x 40 dots at the resolution of 640ppi was realized and illuminated with UV rays to confirm that red, green and blue dots separately emitted light. The emission of red, green and blue lights was also confirmed in a test involving the application of voltage rather than illumination, confirming its correct performance.
These results open new opportunities, such as using the novel photolithography in a multiple patterning process. An example would be creating an OLED array that adds a fourth color to red, green and blue, as well as developing previously-unseen devices such as a new sensors that integrate OLED with the organic photodetector.