H-2 gas-sensing characteristics of SnOx sensors fabricated by a reactive ion-assisted deposition with/without an activator layer

SnOx-based gas-sensor devices have been fabricated by a reactive ion-assisted deposition technique. SnO2 films of 400 Angstrom thickness are deposited on sputtered amorphous SiO2 substrates and then Pt films (600 Angstrom) are sputtered on top of them as upper electrodes. From XRD and TEM studies, as-deposited SnOx films are seen to be amorphous and become polycrystalline after annealing at 500 degrees C in air. In quantitative XPS analyses, the O/Sn atomic ratio in the annealed films shows the nearly stoichiometric value of two and the binding energy of Sn 3d(5/2) is 486.43 eV, very close to 486.75 eV of the standard tin oxide powder. When sensitivity is defined as a relative decrement in resistance, these sensor devices show nearly 100% sensitivities to 1000-5000 ppm H-2 in air at 200 degrees C and above. By attaching an ultra-thin metal activator, the response time can be reduced to less than one tenth of its previous value.