Room-temperature semiconductor gas sensor based on nonstoichiometric tungsten oxide nanorod film

Abstract

Porous tungsten oxide films were deposited onto a sensor substrate with a Si bulk-micromachined hotplate, by drop-coating isopropyl alcohol solution of highly crystalline tungsten oxide (WO2.72) nanorods with average 75 nm length and 4 nm diameter. The temperature-dependent gas sensing characteristics of the films have been investigated over the mild temperature range from 20 to 250 ° C. While the sensing responses for ammonia vapor showed increase in electrical conductivity at temperatures above 150 ° C as expected for n-type metal oxide sensors, they exhibited the opposite behavior of unusual conductivity decrease below 100 ° C. Superb sensing ability of the sensors at room temperature in conjunction with their anomalous conductivity behavior might be attributed to unique nanostructural features of very thin, nonstoichiometric WO2.72. © 2005 American Institute of Physics.