A novel patterning technique for high-resolution RGB-OLED-displays: Laser induced local transfer (LILT)
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A novel patterning technique for high-resolution RGB-OLED-displays: Laser induced local transfer (LILT) Michael Kröger1, Marc Hüske2, Thomas Dobbertin1, Jens Meyer1, Henning Krautwald1, Thomas Riedl1, Hans-Hermann Johannes1 and Wolfgang Kowalsky1 1 Institut fuer Hochfrequenztechnik, TU Braunschweig, Schleinitzstr. 22, 38106 Braunschweig, Germany 2 LPKF Laser & Electronics AG, Osteriede 7, 30827 Garbsen, Germany Abstract A novel patterning technique for high-resolution full-color OLED-displays will be discussed. Currently applied production systems for OLED-displays incorporate a shadow masking system for patterning of single red, green and blue pixels. Due to its limited scalability, alternative techniques, which can be applied to larger substrate sizes, have to be developed. One approach can be the laser induced local transfer of organic materials. An infrared absorbing substrate (target) is coated with either a red, green or blue light-emitting organic material and placed in a short distance (below 50 µm) of the OLED-substrate onto which the organic material is to be patterned. The laser beam is deflected by a scanner onto the target in single lines. If the scanning speed and the laser power are adjusted properly, the target locally heats up to a temperature at which the organic material sublimes and condenses on the opposing OLED-substrate. By repeating this process for each colour red, green and blue stripes can be deposited. Line widths below 70 µm have been achieved. Introduction In the past two decades intense research on organic light emitting diodes (OLED) led from first simple but convincing hetero-structure devices [1] to highly efficient light sources reaching nearly 100 % internal quantum efficiency [2]. This progress was mainly driven by OLEDs being the most promising technology for low-power high-quality flat-panel displays (FPD) and its predicted market volume. OLEDs are competing with several other FPD technologies, among which liquid crystal displays (LCD) are leading the market share. Due to LCD’s viewing characteristics being drastically improved within the last decade, the demands to be fulfilled by OLED displays increased. Only full-colour high-resolution OLED displays will be marketable on a large scale. Furthermore, competitive costs can in the long term only be reached by mass production with substrate sizes comparable to those of LCD production lines (> 1 m2). There are mainly three different approaches of realizing full-colour OLED-displays (OLED: organic light emitting diode). One of these is colour from white by applying a colour-filtermatrix to a white-light emitting OLED-display. Another approach is to convert blue light into green and red light by a colour-converting phosphor matrix (colour from blue). Micro-patterning of red, green and blue OLEDs on one substrate is to be favoured for reasons of lower costs and higher efficiency. Shadow masking is the most common patterning technique for vacuum-deposited OLEDs. For this technique a metal mask is placed in a short distance fro
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