Bilayer Structures of NiOx and Pd in Surface Acoustic Wave and Electrical Gas Sensor Systems |
| W.P. Jakubik, M. Urbańczyk, E. Maciak and T. Pustelny
Institute of Physics, Silesian University of Technology, Krzywoustego 2, 44-100 Gliwice, Poland |
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| A bilayer sensor structure of nickel oxide NiOx ( ≈ 60 nm) with a very thin film of palladium (Pd ≈ 18 nm) on the top, has been studied for gas sensing application at relatively low temperatures of about 30°C and 60°C. The bilayer structure was obtained by rf sputtering and by vacuum deposition (first the NiOx and then the Pd film) onto a LiNbO3 Y-cut Z-propagating substrate, making use of the surface acoustic wave method, and additionally (in the same technological processes) onto a glass substrate with a planar microelectrode array for simultaneous monitoring of the planar resistance of the layered structure. Such a bilayer structure was investigated in a low concentration range (from 50 ppm to 400 ppm in air) of nitrogen dioxide (NO2), carbon monoxide (CO) and ammonia (NH3) in a dry and wet air atmosphere and in a medium hydrogen concentration (1-2.5%) in dry air. The NiOx and Pd bilayer structure interact rather weakly with NO2 molecules but with CO and NH3 this interaction is much greater, especially at higher temperature ( ≈ 60°C). The hydrogen sensitivity is on the medium level, not exceeding 600 Hz (relative change in the differential frequency of ≈ 2.3%) at interaction temperature of 35°C. |
| DOI: 10.12693/APhysPolA.116.315 PACS numbers: 43.25.Fe, 77.65.Dq, 43.35.Pt, 68.35.Iv, 07.07.Df |