Highly sensitive hydrogen sensor based on suspended, functionalized single tungsten nanowire bridge

A highly sensitive hydrogen sensor based on suspended and functionalized single tungsten nanowire is presented. The sensing tungsten nanowire is synthesized by focused ion beam-chemical vapor deposition (FIB-CVD) using W(CO)6 precursor gas on batch-fabricated microelectrodes. The nanowire measures 10 μm in length and 150 nm in diameter, and is suspended 50 μm above the wafer substrate connecting two microelectrodes to enhance the exposure of nanowire surface to target gas molecules for improved chemisorptions. The nanowire is then functionalized by palladium–platinum (Pd–Pt) sputtering process to be sensitive to the hydrogen molecules. The significant increase of nanowire resistance is observed whenever it is exposed to hydrogen molecules, and the resistance is recovered to the original value after hydrogen molecules are purged out. The experimentally characterized hydrogen sensor shows 11.52% increase of resistance to the exposure to 1% (10,000 ppm) hydrogen and 99% nitrogen gas mixture at room temperature and atmospheric pressure. The lowest hydrogen concentration measured is 0.001% (10 ppm) with 0.58% corresponding resistance increase.