Hybrid microfabrication of 3D pyrolytic carbon electrodes by photolithography and additive manufacturing

We report a novel hybrid method for fabricating high aspect ratio 3D pyrolytic carbon electrodes combining UV photolithography and additive manufacturing with commercially available SLA 3D printers and materials. By using a 3D printed chip holder, aligned 3D printing on a patterned silicon chip was possible. This allowed for the fabrication of cylindrical polymer micropillars with a height of 2173 ± 26 μm and a width of 316 ± 11 μm on SU-8 precursor structures defining the leads, contact pads and underlying 2D electrode prepared using UV lithography. Microfabrication of 3D structures with these dimensions is impossible to achieve with SU-8 photolithography alone. The hybrid polymer structures were converted into 3D carbon electrodes with high structural integrity using a 3-step pyrolysis process optimized for the specific 3D print resin. During this process, the micropillars shrunk to 30 ± 3% in height and 35 ± 1% in width of the polymer precursor structures, while maintaining the macroscopic shape and microscopic surface roughness. Electrochemical experiments confirmed that the pyrolytic carbon formed a monolithic conductive 3D electrode. The surface roughness contributed to a 17 ± 5% increase in electroactive surface area compared to the geometrical surface area of the micropillars.