Design and fabrication of differently shaped pyramids on Si{100} by anisotropic wet etching

We aimed to produce differently shaped pyramids, that is, eight-sided, triangular, and rhombic pyramids, on the same Si{100} wafer by simply changing mask patterns. A triangular pyramid has an advantage in that it can always become sharp because its vertex becomes a point and is not affected by fabrication errors. A rhombic pyramid that looks like an arrow head was designed to decrease the insertion friction and scar area even if it is inserted deeply into the skin. Triangular and H-shaped etching mask patterns were designed to produce triangular and rhombic pyramid structures on Si{100} on the basis of eight-sided pyramid formation. Both triangular and rhombic pyramids were successfully fabricated as new MEMS structures by applying TMAH anisotropic wet etching (25.0 wt%, 70 °C). A sharp tip with a radius of less than a few hundred nm was obtained in both the triangular and rhombic Si pyramids.