Enhanced surface capacitance of cylindrical micropillar arrays

While surface capacitance is utilized widely for sensing and actuation in miniaturized systems, relatively little attention has been paid to its enhancement using engineered surface topography. We present how an engineered surface topography, specifically a cylindrical micropillar array, gives a significant enhancement of the surface capacitance compared to a flat surface of the same area. Arrays of silicon micropillars were fabricated and measured, and the results were validated using both an approximate analytical model and a numerical finite element model. At large gaps (hundreds of microns) between a flat probe and the top surface of the array, the capacitance is comparable to that of a flat surface, while at smaller gaps (<200 μm) the contribution of the side surface leads to enhancement of the capacitance. We demonstrate that parametric variation of the array geometry and gap can result in greater than 100% enhancement, while using materials and dimensions compatible with standard microfabrication processes. Therefore, we expect that this engineered surface design can improve the performance of traditional capacitance probes as well as emerging applications such as flexible tactile sensors.