Pd-gate MIS hydrogen sensors exhibit serious drift and decrease of sensitivity. The authors show that the drift is eliminated for a Pd/Pt-hydrogen-sensing gate and Ag/Cu/Pd/Pt-reference-gate differential-type sensor. The decrease of sensitivity for long-term operation can be minimized by high temperature annealing in air. The decrease of sensitivity after 1000 hours operation is less than 10%. It is believed that the decrease of sensitivity is due to a decrease of hydrogen adsorption sites on the Pd gate surface, which becomes oxidized at high temperature operation in air. This oxidation is observed with XPS and AES. The sensitivity decreases abruptly at 100 degree C operation and below, due to water adsorption on Pd surface As evidence for this phenomenon, H//2 O and OH peaks are observed in FTIR spectra for Pd powder at 1% hydrogen gas in synthetic air, and the solubility of Pd metal is abruptly decreased at 100 degree C operation and below.
|Number of pages||3|
|Publication status||Published - 1985 Dec 1|
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