SPRAY CVD DEPOSITION AND CHARACTERIZATION OF SURFACE MODIFIED ZINC-OXIDE THICK-FILMS FOR GAS SENSOR

Polycrystalline ZnO films of thicknesses between 4-mu-m and 11-mu-m and sheet resistance R(sh) between 8 x 10(5) and 7 x 10(6) ohm-open-square-box were prepared by the spray/CVD technique from a solution of 0.4M Zn-acetate containing .004M Al-nitrate solution for Al-doping. A few drops of conc. acetic acid was added to stabilise the solution against hydrolysis. Films were deposited onto borosilicate glass plates at the temperature range 270-degrees-300-degrees-C. R(sh) of the film was as usual found to decrease with an increase in thickness. The surface of the films was sensitized by dispersing noble metals like Pt and Pd during deposition. The electrical properties of these films were studied as a function of temperature and hydrogen flow time. The decrease of the ZnO space charge barrier in the presence of hydrogen due to desorption of chemisorbed oxygen and the release of electrons was found to be the possible mechanism of increased conductivity. Pt and Pd sensitisation activated the desorption process.