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The Laser User Magazine
Issue 053 - Winter 2008
Ultrafast laser patterning of OLEDs for solid-state lighting
Author: Dimitris Karnakis
Traditionally, laser micromachining has relied on Q-switched Diode-Pumped Solid State (DPSS), excimer and CO2 lasers of typically nanosecond (ns) pulse duration or longer. These lasers offer relatively high average power and can achieve high volume removal rates harnessing a combined etching effect from laser and laser-induced plasma processes. As a result, micro-drilling, scribing and fine cutting applications have benefited on an industrial scale. However, the driving mechanism even at short wavelengths is strongly thermal in nature. This arises largely as a result of secondary plasma heating of the target and substrate thermal conduction, and it limits fine control of the ablation process. Undesirable side effects near the irradiated regions such as micro-cracking or edge chipping, burr formation and particle debris that often accompany the micromachining process confirm this claim. As a result, successful laser machining with ns lasers is still viewed by many as a ‘black art’. However, with the ever-increasing miniaturisation of products and processes, this picture is changing rapidly.
Design and technology trends The trends in most advanced technological applications are towards using material layers as thin as possible (e.g. sub-micron) and offering increased functionality involving complex multi-layered structures. Combinations of thin metals, metal oxides, ceramics or organic layers on glass, metal or polymer substrates are typically encountered, most of the layers being optically and thermally thin. Selective laser patterning of such layers is not a simple task and achieving an industrially robust process becomes very challenging.