Low Concentration Response Hydrogen Sensors Based on Wheatstone Bridge

The PdNi film hydrogen sensors with Wheatstone bridge structure were designed and fabricated with the micro-electro-mechanical system (MEMS) technology. The integrated sensors consisted of four PdNi alloy film resistors. The internal two were shielded with silicon nitride film and used as reference resistors, while the others were used for hydrogen sensing. The PdNi alloy films and SiN films were deposited by magnetron sputtering. The morphology and microstructure of the PdNi films were characterized with X-ray diffraction (XRD). For efficient data acquisition, the output signal was converted from resistance to voltage. Hydrogen (H-2) sensing properties of PdNi film hydrogen sensors with Wheatstone bridge structure were investigated under different temperatures (30 degrees C, 50 degrees C and 70 degrees C) and H-2 concentrations (from 10 ppm to 0.4%). The hydrogen sensor demonstrated distinct response at different hydrogen concentrations and high repeatability in cycle testing under 0.4% H-2 concentration. Towards 10 ppm hydrogen, the PdNi film hydrogen sensor had evident and collectable output voltage of 600 V.