Fabrication of Highly-ordered and Densely-spaced Silicon Nano-needle Arrays for Bio-sensing Applications

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0900-O11-02.1

Fabrication of Highly-ordered and Densely-packed Silicon Nano -needle Arrays for Bio-sensing Applications Aijun Yin and Jimmy Xu Division of Engineering, Brown University, Providence, Rhode Island 02912 ABSTRACT 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. INTRODUCTION Great efforts have been expended to develop reliable techniques for the fabrication of highly ordered three-dimensional nanostructures which are expected to have great potential impacts in many fields, such as chemical and optical sensors,1, 2 and biological sensors3-5 . For example, in the case of intracellular sensing, it is highly desirable to form small (nanometerscale), long (micrometer-scale), strong, and electrically active but chemically inert probing needles. Such nano-needles are challenging to make by traditional methods. Moreover, for most applications, these nano- needles need to be mechanically anchored in and electrically interfaced with a solid micro (or macro) base. For ease of integration with control electronics, silicon compatible technology or technology permitting monolithic integration are preferred 6 . Furthermore, for many applications including intracellular probing and explorations, these probing nano-needles should be vertically aligned and parallel to each other, uniform in height and diameter, and densely spaced in an array form. All these requirements and desirables are generally hard to meet by conventional micro or nano- fabrications. Yet, for any new method to be viable, it needs to be kept simple, scalable and low-cost. Electron beam lithography (EBL)7 and focused ion beam lithography (FIB)8 are capable of fabricating sub-50-nm patterns, but they are limited by their low throughput.. Thus, alternative and unconventional methods for producing large array of nanostructures are being pursued actively 9-15 . Of these approaches, the nonlithography method using anodic aluminum oxide (AAO) membranes as evaporation or dryetching mask appears most promising for scalable fabrication of la

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