Humidity sensing characteristics of focused ion beam-induced suspended single tungsten nanowire

We demonstrated humidity sensing characteristics based on a suspended single tungsten nanowire. The nanowire is synthesized on batch-processed microelectrodes by focused ion beam-chemical vapor deposition (FIB-CVD) using tungsten hexacarbonyl [W(CO)6] as the precursor gas. Two different humidity sensing mechanisms, electrothermal sensing and chemical sensing, were demonstrated using as-deposited and annealed nanowires. When the relative humidity level was increased from 30% to 80%, the DC resistance of the as-deposited nanowire immediately showed 5.68% decrease by electrothermal sensing mechanism. Since the as-deposited nanowire is amorphous structure, no chemical sensing response was observed for the as-deposited nanowire case. On the contrary, the tungsten nanowire annealed at 700°C showed a 13.2% increase in its DC resistance by the chemical sensing mechanism when the relative humidity level was increased from 40% to 80%, revealing enhanced sensor responsiveness and improved linearity than the electrothermal sensing using as-deposited nanowire.