In this work, we report a success in fabricating highly-ordered and densely-packed array of silicon nano-needles that are vertically aligned, straight and long, meeting many of the requirements for biomolecular sensing and integration with silicon electronics. Yet, we show that they can be fabricated with a relatively simple and non-lithographic method.
In this approach the array of nano-needles of high uniformity in length and diameter are made out of silicon by reactive ion etching (RIE) through either an anodic aluminum oxide (AAO) membrane or an array of metallic nano-dot caps that are evaporated on a silicon wafer using an AAO membrane as mask. The AAO membrane itself is formed non-lithographically via anodization of pure aluminum foil and contains an array of highly-ordered and highly-uniform nano-pores. By using the AAO membrane either directly as an etching mask or as an evaporation mask to deposit metallic nanodots which in turn serve as an etching mask, deep and high aspect-ratio etching is possible to allow the formation of the nanoneedles in a Si substrate.