| Abstract | We report a new technique for fabricating metal nanoring array. In the process, a Cr nanodisk array was first formed by evaporating Cr onto the bottom of a 200 nm period hole array having large undercut. The hole array was produced by NIL and RIE pattern transfer in a polymer sandwiched between a thin SiO₂ and Si layer, which were stacked on a second polymer layer; and the undercut was formed by excessive polymer RIE. The thin Si surrounding the Cr disk was subsequently etched through by SF₆ RIE, resulting in a ring-shaped hole structure in Si. After removing SiO₂ and the first polymer layer and etching through the second polymer layer, a metal ring array was created by standard evaporation and liftoff. As examples, we fabricated Cr nanoring array with height 15 nm, inner diameter 70–120 nm and ring-width down to 22 nm. We have found that, for a fixed hole diameter, the ring-diameter is strongly dependent on the hole depth. The ring symmetry and the wafer edge effect are discussed. The process can certainly be extended to metals other than Cr. Compared to previous methods, the current one is simpler, less costly and more suitable for narrow ring fabrication, though it suffers from reduced ring symmetry. However, asymmetric (nonconcentric) nanoring could be desirable for magnetic data storage and plasmonic devices. |
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