LOW-PRESSURE CHEMICALLY VAPOR-DEPOSITED WO3 THIN-FILMS FOR INTEGRATEDGAS SENSOR APPLICATIONS

The gas sensing proper-ties of substoichiometric WO3 films have been i nvestigated when activated with some gold monolayers sputtered on thei r surface and in the as-deposited form. These films were deposited on silicon substrates, in two steps: (i) chemical vapor deposition of tun gsten films using W(CO)(6) vapors in a horizontal cold wall reactor at a pressure of 13.3 Pa and temperatures between 773 and 823 K, and (ii ) oxidation of the tungsten films in air at 873 K for 10 min. For the tests, the substoichiometric WO3 films were packed in classic dual in- line packages. The resistance variations of these configurations cause d by changes in their environment were monitored. Reversible changes, of the order of several kilohms, were observed in th presence, or upon removal H-2, at concentrations down 100 ppm, the magnitude of which d epended on the concentration and the temperature measured. The respons e times measured were also dependent on temperature and H-2 concentrat ion, and were of the order of some minutes.