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Orthogonal photolithography for high resolution OLED-micro displays
The Fraunhofer COMEDD is looking into new approaches for the structuring of micro-OLEDs. Orthogonal photolithography allows for smaller pixel gaps while keeping the same brightness levels – making the material more viable for augmented reality applications.
Image: Fraunhofer COMEDD.
“The orthogonal photolithography is a patented technology, allowing for a direct structuring of organic materials on CMOS-backplanes”, says Dr. Alexander Zakhidov, leader of the development group. “Now, high resolution OLED-microdisplays for headmounted displays and data glasses with a brightness of 5000 cd/ m² are possible.” Micro displays with a brightness of this degree are needed for applications in augmented reality, because the virtual picture has to be visible in broad daylight.
The direct RGB-pixel-structuring with traditional technologies – such as the usage of shadow masks, enabling a pixel gap of ca. 50 µm – faces several constraints. Until now, smaller pixel gaps could only be accomplished by coating all subpixels with white OLED and applying a color filter. The filter can separate red, green and blue subpixels. This has the disadvantage of causing brightness loss, because ca. two thirds of the spectral range are suppressed and only 10-20 % of the radiated light can actually be used.
The new technology developed by Fraunhofer utilizes the fact that almost all organic material is either hydrophob or hydrophil, which makes it indissoluble by highly fluoridated chemicals. This means that certain fluoridated photo coatings can be used for the structuring of organic layers, without compromising the capability of the organic elements.
Enabling higher resolutions OLEDs that can keep the brightness levels needed for daylight, the Fraunhofer research results may be a viable addition to augmented reality applications of tomorrow.
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