OLED patterning technique focuses on high-brightness data glasses
“Orthogonal Photolithography is a patented technology, which allows direct patterning of organic material on CMOS-backplanes,” explained Dr. Alexander Zakhidov, leader of the development group. “So, high-resolution OLED microdisplays for head-mounted displays and data eye-glasses with brightness of 5000 cd/m² are now possible.” High brightness micro-displays are required for augmented reality applications where the virtual image has to blend in smoothly with the daylight environment.
The limit for direct RGB-pixel patterning is given by conventional technologies like shadow masking, enabling pixel pitches of about 50 µm. Today smaller pixel pitches can be realized only by covering all sub-pixels with a white OLED and adding a color filter. The filter is able to separate red, green and blue sub-pixels. The disadvantage is, that the color filter causes enormous losses in the light brightness and brilliance. The reason is, that approximately 2/3 of the spectral range of the white pixels are always cut off for the colors that are not needed, and white OLED is itself less efficient than monochrome, which means that 10 to 20 % of the emitted light could be used.
The orthogonal photolithography technology takes advantage of the fact that the majority of organic materials are either oleophilic or hydrophilic and are hence orthogonal (insolvable and stable) to highly fluorinated chemicals. Appropriate fluorinated photoresists can be used to pattern organic layers without compromising of performance of the organic device. The availability of such orthogonal photoresists promises to enable the fabrication of complex device structures, expanding the range of possibilities for organic electronics.
Fraunhofer COMEDD established Orthogonal Photolithography in organization’s clean room and incorporated it into 200 mm wafer micro display pilot fabrication line. The scientists offer the technology for joint developments of OLED microdisplays and OLED micro-signage applications together with industrial partners.
Fraunhofer COMEDD capabilities for 200 mm wafer processing include:
300 m2 clean room class 100
Resist deposition/processing with uniformity deviation <1%
Resolution 1 µm
Alignment precision 1 µm
Wet bench for cleaning/etching
Dry RIE etching via Ar ion mill and O2 plasma
Batch vacuum/N2 oven, hotplates Air/N2
Optical inspection, particle control
At the SID 2014 event in June 2014, Fraunhofer COMEDD plans to show the first results of the technology.
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