European research institute imec and Chunghwa Picture Tubes Ltd. (CPT) in the framework of the Holst Centre collaboration showcased an ultra-high resolution display. CPT and imec employed photolithography patterning of OLED arrays to produce the display. According to imec and CPT, the results could lead to cost-effective fabrication of fine, side-by-side pixels in OLEDs. CPT and imec are presenting the ultra-high resolution display at the annual International Smart Display and Touch Panel Exhibition, Touch Taiwan, in Taipei, Taiwan ROC, Sep 20 – Sep 22.
Active-matrix organic light-emitting diode (AMOLED) displays with discrete light emitting pixels are steadily growing in their market share and in their achievable resolution, size, brightness, and lifetime. However, in order to continue advancing this technology, imec along with its program partners are investigating an economical production approach for OLED arrays featuring fine pixels.
Furthermore, the research partners see pushing the pixel density beyond 1000 ppi as a necessary step for implementing next-generation displays, especially those used in virtual and augmented reality. CPT and imec have verified that their novel photolithography process can permit ultrafine OLED patterns. The proposed technique does not require the use of fine-metal masks to structure thermally evaporated OLED stacks (“FMM-free”).
One primary difficulty when utilizing standard photolithography is the fragility of the organic materials used as photolithography chemicals. imec and CPT have managed to avoid this problem using an i-line, chemically amplified photoresist system as part of a process dedicated to fabricating OLED stacks.
In addition to enabling ultra-high resolution AMOLED displays, other benefits of photolithography include good yield control, high aperture ratio, and large substrate size compatibility.
CPT and imec Demonstrated Proof of Concept
CPT and imec demonstrated a proof of concept for the fabrication process by producing a passive display with 1400×1400 pixels (1.96 megapixel) of side-by-side, orange and green OLEDs. The sub-pixel pitch of just 20 μm translates to the equivalent resolution of 1250 ppi. Uniform electroluminescence can light up each color separately. Moreover, a preliminary lifetime examination revealed that each color after patterning was able to operate for a few hundred hours while maitaining more than 50% of the original brightness.
“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,” stated Paul Heremans, program director of thin-film electronics at Holst Centre/imec. “The collaboration with CPT enables us to improve the manufacturability readiness level of the OLED photolithography patterning method. This will enable production of ultra-high resolution OLED displays for next-generation user interfaces. We are very happy to have the possibility to explore this exciting technology route with our innovative partners.”