Patterning of ITO with picosecond lasers

Indium-tin oxide (ITO) is the main material for making transparent electrodes in electronic devices and flat panel displays. Laser-direct-write technology has been widely used for patterning ITO. The well defined edges and good electrical isolation at a short separation are required for the modern OLED and RFID devices of high packing density. High repetition rate lasers with a short, picosecond pulse width offer new possibilities for high efficiency structuring of transparent conductors on glass and other substrates. The results of patterning the ITO film on glass with picosecond lasers at various wavelengths are presented. Laser radiation initiated ablation of the material, forming trenches in ITO. Profile of the trenches was analyzed with a phase contrast optical microscope, a stylus type profiler, SEM and AFM. Clean removal of the ITO layer was achieved with the 266 nm radiation when laser fluence was above the threshold at 0.20 J/cm2, while for the 355 nm radiation the threshold was higher, above 0.46 J/cm2. The glass substrate was damaged in the area where the fluence was higher than 1.55 J/cm2. The 532 nm radiation allowed getting well defined trenches, but a lot of residues in the form of dust were generated on the surface. UV radiation at the 266 nm provided the widest working window for ITO ablation without damage of the substrate. Use of UV laser radiation with fluences close to the ablation threshold made it possible to minimize surface contamination and the recast ridge formation during the process.