Design of anodically oxidized metal oxide films as a gas sensor material

H/sub 2/ sensing properties of an anodically oxidized Nb/sub 2/O/sub 5/ film coupled with a noble metal electrode (M/Nb/sub 2/O/sub 5/, M:Au, Pt and Pd) have been investigated under various operating conditions. Among the sensors tested, the Nb/sub 2/O/sub 5/ film with a Pd electrode, which was prepared by anodic oxidation in an aqueous solution of 0.5 M H/sub 2/SO/sub 4/, showed the highest H/sub 2/ response, and the logarithmic sensor current under a forward bias was proportional to the logarithmic H/sub 2/ concentration. The current-voltage characteristics of the Pd/Nb/sub 2/O/sub 5/ sensor at 100/spl deg/C apparently showed a typical rectifying function of a metal-semiconductor junction, which was formed between the Pd electrode and the Nb/sub 2/O/sub 5/ thin film, especially in H/sub 2/ balanced with dry air. The H/sub 2/ response property was improved when it was operated under a forward bias above 150/spl deg/C. Furthermore, it was confirmed that even at 28/spl deg/C the Pd/Nb/sub 2/O/sub 5/ could respond to H/sub 2/ in dry air.