Fabrication of Novel Hollow Micro Needles for Biological Applications
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Fabrication of Novel Hollow Micro Needles for Biological Applications Z. Sanaee, S. Mehrvarz, M. Mehran, M. Abdolahad, M. Sohrabi and S. Mohajerzadeh Nano-electronic Center of Excellence, Thin Film and Nano-Electronic Lab, School of Electrical and Computer Eng, University of Tehran, Tehran, Iran, [email protected]
ABSTRACT Microneedles have applications in drug delivery and biotechnology. We report a novel needle-like hollow cylindrical structure as a base for the growth of carbon nanotubes (CNT) to form a cage-like structure. The formation of hollow microneedle structures is feasible on Si-membranes using proper patterning of the masking layer and combined by a deep reactive ion etching. The formation of highly featured structures at micro and nanometric scale is reported. By controlling the etching parameter one is able to achieve three-dimensional as well as highly vertical structures on silicon substrates. The growth of carbon nanotubes on such structures allows the realization of cage-like carbon-based features which could be suitable for gas and liquid transport.
I. INTRODUCTION Deep reactive ion etching (DRIE) of silicon is a powerful tool to realize highly sophisticated features on silicon substrates. Apart from frequent applications in micro-electromechanical systems (MEMS) and sensors, this method has found novel applications in the biotechnology. Smart drug delivery as well as the formation of fine electrodes for electro-cardiographs (ECG) are all outcomes of this critical process [1,2]. Recently by using a silicon nano-rod as the tip of an AFM apparatus, researchers have been able to perform gene delivery and cell manipulation [3]. As a main milestone in the realization of such nano and micro structures, a process called as Bosch process was introduced to take advantage of a sequential etching and passivation process in a high density inductive coupled plasma system [4]. The high precision etching allows the evolution of micro and nano-rods as well as complex arrays of interdigital structures. Generally, Bosch process uses a polymeric coating during the passivation cycle whereas this layer is removed in the subsequent steps using an inductively coupled RF-plasma. In another process, called as cryogenic etching, intensive cooling of the silicon substrate to cryogenic temperatures by means of liquid nitrogen is practiced [4]. Recently we have developed a hydrogen assisted deep reactive ion etching (HDRIE) technique which replaces the polymeric passivation in Bosch process by a combination of hydrogen/oxygen and SF6 gases to obtain high aspect ratio features with no need to high density plasmas [5]. Silicon-based hollow out-of-plane micro-needles were first realized by using a combination solid needle formation and deep reactive ion etching to realize hollow features [6-7]. This latter step requires the use of optical mask alignment. In a similar attempt the use of Ni electroplating on previously- realized solid-needles have been exploited to form hollow structures [7]. Most recently the formation of SiO2-
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