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1253-K08-04

Controlled Fabrication of Nanostructure Material Based Chemical Sensors Laura J. Evans1, Gary W. Hunter1, Jennifer C. Xu1, Gordon M. Berger2, and Randall L. Vander Wal2* 1 NASA Glenn Research Center, Cleveland, OH 44135, U.S.A. 2 USRA at NASA GRC, Cleveland, OH 44135, U.S.A. * currently at The Pennsylvania State University, University Park, PA 16802, U.S.A. ABSTRACT In this paper, we report on a processing approach for a microsensor platform that incorporates nanorods in a controlled, efficient, and effective manner. Using this novel approach of combining dielectrophoresis with standard microfabrication processing and materials, we have achieved reproducible, time-efficient fabrication of gas sensors with buried contacts to the tin oxide (SnO2) nanorods used for the detection of gases. The steps associated with this approach are described in detail. Semiconducting SnO2 nanorods are used to demonstrate this approach. The SnO2 nanorods succeeded as sensing elements for the detection of hydrogen (H2) and propylene (C3H6) up to 600oC, as well as the detection of nitrogen oxides (NOx) at 400oC. This investigation shows the combination of nanorods and standard microfabrication processing materials resulting in a new technique for the fabrication of chemical microsensors using nanomaterials. INTRODUCTION Applications for chemical sensing include environmental monitoring, fire detection, emissions monitoring, and biochemical sensing. Metal – oxide semiconductors such as tin oxide (SnO2) have been shown to respond to relevant chemical species such as oxygen (O2), carbon monoxide (CO), ethanol (C2H5OH), NOx, C3H6, and H2 [1]. The use of nanotechnology based materials for chemical sensing has been of great interest since nanocrystalline materials have been shown to offer improved sensor sensitivity, stability, and response time [2]. Several groups are successfully integrating nanostructures, such as nanowires or nanorods, into operational sensors [3-4]. The typical procedure may include random placement (e.g., dispersion, with fineline or coarse patterning techniques used to create functional sensors) or time consuming precise fabrication (e.g., mechanical placement using an atomic force microscope or laser tweezer techniques). Contact printing techniques have also been used (e.g., use of a Langmuir-Blodgett trough or Superlattice Nanowire Pattern Transfer) but do not combine the alignment technique with subsequent deposition of electrical contacts [5-6]. Dielectrophoresis (DEP) has also been utilized, however it can be challenging to achieve good electrical contact of the nanostructures to the underlying electrodes. In the present work, DEP has been combined with conventional photolithography in order to fabricate chemical gas sensors with an ordered arrangement of nanorods, as well as dependable contacts. This paper concentrates on the fabrication process steps, while a more detailed journal article is intended to investigate the ramifications of this approach to sensor technology [7].

EXPERIMENT The SnO2 nano