CPT, imec/Holst Centre Demonstrate 1250 ppi, FMM-free Multicolor OLED Displays with Photolithography

Chunghwa Picture Tubes Ltd. (CPT), together with imec in the framework of the Holst Centre collaboration, showcased an ultra-high resolution display realized by photolithography patterning of organic light emitting diode (OLED) arrays.
 
The results pave the way to cost-effective manufacturing of fine, side-by-side pixels in OLEDs, and were presented at the annual International Smart Display and Touch Panel Exhibition, Touch Taiwan, in Taipei, Taiwan ROC, Sept. 20-22.
 
High quality displays are at the core of modern, connected society, with mobile screens enabling and enhancing an ever-increasing number of daily appliances. Active-matrix organic light-emitting diode (AMOLED) displays, with discrete light emitting pixels, are steadily growing, not only in market share, but also in achievable resolution, brightness, size and lifetime.
 
To continue the advancement of this technology, imec together with its program partners are researching a cost-effective manufacturing method for OLED arrays featuring fine pixels. Pushing the pixel density beyond 1000 ppi is a necessary step for implementation of next-generation displays, especially for virtual and augmented reality.
 
CPT and imec have verified that a novel photolithography process can allow for ultrafine OLED patterns. The proposed technique does not require using fine-metal masks to structure thermally evaporated OLED stacks (FMM-free).
 
One of the main challenges when applying standard photolithography is the fragility of the organic materials for the photolithography chemicals. To circumvent this issue, imec and CPT have used an i-line, chemically amplified photoresist system in a process flow dedicated to OLED stacks. Apart from ultra-high resolution, other benefits of photolithography include high aperture ratio, large substrate size compatibility and good yield control.
 
The proof-of-concept is a passive display with 1400×1400 pixels (1.96 megapixel) of side-by-side, orange and green OLEDs. The sub-pixel pitch of 20 μm results in the equivalent resolution of 1250 ppi.
 
“Our goal is to identify and explore technology bottlenecks in the extremely competitive and fast-paced display industry. With research activities spanning from material and device science, through design, fabrication and integration all the way to tech transfer, we make use of our semiconductor and thin-film background,” said Paul Heremans, program director of thin-film electronics at Holst Centre/imec.

Multicolor OLED display from CPT, imec and Holst Centre. (Source: imec)