Fabrication of aluminum electrodes by water and light

Rapid fabrication of 1-5-μm-wide aluminum electrodes by a flexible, inexpensive and high-resolution process is demonstrated. The electrodes are produced by scanning a cw focused laser beam of 488 nm wavelength over an aluminum thin film of 50-100 nm thickness immersed in pure water and removing the metal by local low-power laser-thermal corrosion. The process is performed on a set-up operating in common laboratory conditions. The aluminum patterning requires only several milliwatts of laser light, which allows the use of inexpensive light sources and makes it especially suitable for structuring metal films on heat-sensitive materials such as polymers. Interdigitated microelectrode arrays on poly(dimethylsiloxane) and SU-8 resist are fabricated without damaging the substrate. By taking advantage of the intrinsic 3D processing capability of laser machining and thick film techniques developed for polymer-based microsystems, multilayered electrode structures in SU-8 are produced. Interconnections between the different electrode layers are realized via holes drilled through the intermediate polymer by laser ablation in air and subsequent metallization. The rapid prototyping of an asymmetric electrode array for electrohydrodynamic pumping within 4 h is demonstrated. Successful testing of the device by pumping of water provided evidence of correct electrode operation.