Trace Vapor Detection with Vertical Silicon Nanowire Arrays

Introduction: Semiconducting nanowires and nanotubes have great potential as chemical and biological ChemFET-type sensors in a variety of military, industrial, and commercial applications. For example, the proliferation of improvised explosive devices (IEDs) and recent terrorist attempts demonstrate the need for portable and sensitive sensors for detecting explosives vapors and toxic industrial chemicals (TICs). The most common ChemFET configurations use electrical conductivity measurements across single nanowires or a network of nanowires placed randomly on a surface. Nanowire-based ChemFETs are extremely sensitive to vapors because of their large surface-to-volume ratios; however, they have underperformed as portable, field-deployable sensors. The lower than anticipated performance is due to a combination of factors including variable or uncontrolled doping and dimensions, substrate effects such as adsorption/desorption and trapping on the supporting substrate surface, variable surface structure, occlusion of the analyte by the electrodes, 1/f noise from a reduced number of charge carriers in single nanowire configurations, and shot noise from wire-to-wire junctions in networks of overlapping nanowires.