Thin films of cubic Na0.6WO3, which is one of the sodium tungsten bronze, were fabricated byrf sputtering for the electrode applications in integrated sensors and actuators. A single-phase cubicNa0.6WO3 sputtering target of power type was prepared by conventional solid-state reaction. Thin filmswere deposited from the powder target, and the as-deposited films were amorphous, thus they annealedby tube furnace or RTP for crystallization. Thin films having cubic phase NaxWO3 were fabricated by theoptimization of sputtering and post-annealing conditions, but single-phase cubic Na0.6WO3 thin films werenot obtained. Although the films were not in single phase, they had good electrical conduction propertiesshowing electrical resistivities of 10-4 Ω·cm order.

The powders for the NaxWO3 (x= 1 and 0.75) sputtering targets were synthesized by the calcination in reductive atmosphere. Near single-phase NaWO3 and single-phase Na0.75WO3 powder targets were prepared. By using the targets, thin films of each composition were deposited by rf magnetron sputtering on the SiO2 (100 nm)/Si substrates and annealed by RTP (rapid thermal processing) for crystallization. In the case of the NaWO3 composition, single-phase NaxWO3 thin films, where x was believed to be slightly less than 1, were fabricated accompanying the Na-diffusion into the substrates during RTP. However, in the case of the Na0.75WO3 thin film preparation, it was unable to make single-phase thin films. From the phase formation behaviors of both powders and thin films, it was revealed that NaxWO3 with nonstoichiometric composition of x, which was slightly less than 1, was favorable. The good electrical conduction properties were obtained from the single-phase NaxWO3 thin films. Their electrical resistivities were as low as 7.5 × 10-4 Ω·cm.