Optimization of maskless SU-8 photolithography for fabrication of dense high-aspect-ratio pyrolytic carbon micropillar arrays

This study presents the optimization of maskless UV lithography with SU-8 for the fabrication of 3D electrodes with pyrolytic carbon micropillar arrays. The aim was to maximize the pillar density and enhance the electroactive surface area of the electrodes. For this purpose, the exposure dose at 365 nm wavelength and defocus value in a maskless aligner projecting the image with a spatial light modulator onto the substrate were optimized for fabrication of SU-8 micropillars with heights varying from 25 to 100 μm and diameters ranging from 5 to 40 μm resulting in aspect-ratio of up to 10. The minimal achievable gap in SU-8 micropillar arrays was largely dependent on the defocus value, and gap dimensions identical to the pillar diameter were achieved. The SU-8 precursor structures were successfully converted into carbon micropillar arrays by pyrolysis at 1050 °C with an observed shrinkage of approximately 50 %. 3D carbon microelectrodes were fabricated and electrochemically characterized with cyclic voltammetry and electrochemical impedance spectroscopy. The results indicate that there is a reasonable correlation between microelectrode surface area and electrochemical performance of the electrodes. 3D electrodes with less dense arrays of larger pillars fabricated with initial SU-8 height of 75 μm and 100 μm showed higher peak currents in CV than smaller pillars at higher number densities, reaching a maximum enhancement of approximately a factor 2 compared to 2D electrodes without micropillars. • Optimization of maskless UV lithography for fabrication of SU-8 micropillars with heights varying from 25 to 100 μm. • Successful conversion of SU-8 precursor structures into dense carbon micropillar arrays with a shrinkage of 50 %. • Maximum peak current enhancement of factor 2 in cyclic voltammetry with 3D pillars compared to 2D electrodes.