High Aspect-Ratio, Fully Conducting Gold Micropillar Array Electrodes: Silicon Micromachining and Electrochemical Characterization

In this paper we describe the design, fabrication, and characterization of cylindrical gold micropillar array electrodes. Micropillar array electrodes bring about several advantages compared to planar electrodes and microelectrode arrays, as they provide a much larger surface area than the latter devices. Micropillar array electrodes are closely related to porous electrodes, as suggested by the recent literature and as our experimental results show. We fabricated a number of different gold micropillar array structures using standard microfabrication techniques, particularly DRIE plasma etching, thermal oxidations, and gold metallization by dc sputtering. Experimental results were compared with simulations, and very good agreement was found. This served both to validate the diffusion domain approximation for these particular devices and also to deepen our understanding on the modes of mass transport controlling the current response of these devices. We found that planar diffusion dominates the response of these devices and that thin layer diffusion effects play a crucial role and are responsible for both displacing the position of the peaks and narrowing the peak-to-peak separation in cyclic voltammograms. These effects arise only as a result of the surface topology and should not be mistaken by catalytic effects.