Taiwan-based Chunghwa Picture Tubes (CPT), in collaboration with European research institute imec (in the framework of the Holst Centre collaboration) have demonstrated an ultra-high resolution OLED display that was patterned using photolithography - without the need for an FMM (metal mask). A photolithography process offers a high aperture ratio, large substrate sizes and good yield control.

FMM-free photolithography-made OLED prototype (CPT + imec)

The prototype display that was demonstrated is a passive display with a 1400x1400 resolution (or 1250 PPI!) of side-by-side orange and green OLEDs. imec reports that preliminary lifetime investigation shows operation of each color after patterning for a few hundred hours at more than 50% of the original brightness.

The two companies say that the one of the main challenges when applying standard photolithography to OLEDs is the fragility of the organic materials for the photolithography chemicals. To solve this issue, CPT and imec have used an i-line, chemically amplified photoresist system in a process flow dedicated to OLED stacks.

imec has been developing photolithography patterning for a long time. In 2013 imec and Fujifilm announced a new photoresist-based OLED patterning technology that can enable sub-micron patterns. This research project continued and in 2015 the two companies presented a full-color prototype.

CPT has an existing pilot 4.5-Gen AMOLED fab - used to produce AMOLEDs in very small volume. In recent years CPT has been collaborating with ITRI and FlexEnable to developer flexible AMOLED technologies, and has stated that it will initiate flexible OLED production in 2017.

Some speculate that CPT will use ITRI's technology and also integrate ITRI's existing 2.5-Gen flexible AMOLED production line into its own fab. ITRI is also looking into IGZO and OTFT technologies. CPT is building a new 6-Gen fab in China, with an investment of about $1.85 billion - and some reports suggest that CPT plans to produce IGZO backplane OLED panels in the second phase of this fab. It is great to see CPT also developing novel patterning technologies and assisting the Holst Center's programs.

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