Chemical Sensing with Silicon Nanowires in a Vertical Array with a Porous Electrode

P.E. Pehrsson, D. Ratchford, J. Yeom, S. Rose-Pehrsson, C. Tamanaha, C.R. Field
Naval Research Laboratory, US

Keywords: nanowire, chemical sensors, explosives

Summary:

Field effect transistor-based chemical sensors (ChemFETs) based on nanowires have been researched for military, industrial, and commercial applications as gas phase chemical detectors. They are extremely sensitive to vapors, but have underperformed as portable, field deployable sensors, because of substrate effects, humidity, 1/f noise, and noise from contacts and wire-to-wire junctions. NRL’s chemical sensing architecture using Silicon Nanowires in a Vertical Array with a PORous electrode (SiN-VAPOR). The SiN-VAPOR architecture is fabricated using a metal-assisted wet-chemical etch combined with two-stage nanosphere lithography [1,2]. Vertical silicon nanowires are etched from the silicon wafers, and are then capped by a porous top electrode for rapid analyte access. The vertical configuration reduces maximizes the sensing surface area and number of charge carriers, while reducing substrate effects, noisy wire-to-wire junctions. A Trace Explosives Sensor Testbed with an Impactor-inspired sample chamber for sensor evaluation was constructed and used to characterize SiN-VAPOR sensor performance. Performance was characterized for trace concentrations (sub-parts-per-million) of toxic industrial compounds (TICs), such as ammonia and nitrogen dioxide, and explosives, such as dinitrotoluene (DNT) and trinitrotoluene (TNT). The effects of operating temperature, humidity, flow rate, and sensor configuration were investigated.