Fabrication and integration of metal oxide nanowire sensors using dielectrophoretic assembly and improved post-assembly processing

We report the fabrication and integration of metal oxide nanowire sensors using dielectrophoretic assembly and a novel bonding process. Metal oxide nanowires were successfully prepared by a two-step thermal oxidation process from their corresponding metal nanowires (indium, tin, and indium–tin) that have been synthesized by electroplating in nanoporous templates. Before oxidation, dielectrophoretic (DEP) assembly and a novel post-assembly bonding process were applied to integrate high-density nanowire arrays on interdigitated microelectrodes. Scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDS) elemental analysis provide morphological and compositional informations of the metal and metal oxide nanowires. Electrical measurements of the nanowire arrays show how the resistance changed after each process, which demonstrates that the post-assembly bonding is an important and effective step in reducing contact resistance between the nanowires and interdigitated microelectrodes. Metal oxide nanowire sensor chips were fabricated using microelectrodes embedded with a microheater for temperature control. The performance of these metal oxide nanowire sensors was investigated towards common volatile organic compounds, including methanol, ethanol, isopropanol, acetone, chloroform, and benzene, and the sensors showed high sensitivity, fast response, and good repeatability. The assembly and improved post-assembly bonding processes developed in this research provide a new platform for nanowire-based sensor integration.