This work presents a novel technique for Silicon dioxide microneedles fabrication. Microneedles are hollow microcapillaries with tip diameters in the range of micrometers allowing the fabrication of micro-syringes. These structures are interesting in medical and biological applications, such as DNA injection, antibody manipulation and delivery, or cell manipulation. For the fabrication of the needles, first, macropore formation in n-type silicon is performed by photoassisted electrochemical etching (ECE) in low concentration hydrofluoric acid. Using lithographical patterns the distance between pores can be defined. The microneedles morphology depends on the anodization conditions such as current density, etching time, HF concentration, temperature, bias as well as on substrate properties: doping density and orientation. Afterwards, the etched macropores were oxidized and then the microcapillaries were released using backside TMAH etching. The silicon oxide at the tip of microcapillaries is etched in buffered hydrofluoric acid. The resulting needles can be tailored to the desired shape, for instance to improve mechanical resistance. Microneedles can be fabricated by this method with diameters ranging from less than 1μm to several tens of microns. In this work microneedles arrays were fabricated with pore diameters in the range of 2-5μm, with lengths from 30-140μm and 70nm thick. Microneedles inner diameter can be further adjusted by controlling the thickness of SiO₂ on the walls. In this way inner diameters in the submicron range can be obtained.

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1. FTIR Characterization of Photonic Bands in 2D Silicon Photonic Crystals