Hydrogen sensing properties of Pd-doped SnO2 sputtered films with columnar nanostructures

Pd-doped SnO 2 sputtered films with columnar nanostructures were deposited using reactive magnetron sputtering at the substrate temperature of 300 °C and the discharge gas pressures of 1.5, 12, and 24 Pa. Structural characterization by means of X-ray diffraction and scanning electron microscopy shows that the films composed of columnar nanograins have a tetragonal SnO 2 structure. The films become porous as the discharge gas pressure increases. Gas sensing measurements demonstrate that the films show reversible response to H 2 gas. The sensitivity increases as the discharge gas pressure increases, and the operating temperature at which the sensitivity shows a maximum is lowered. The highest sensitivity defined by ( R a  −  R g ) /  R g , where R a and R g are the resistances before and after exposure to H 2 , 84.3 is obtained for the Pd-doped film deposited at 24 Pa and 300 °C upon exposure to 1000 ppm H 2 gas at the operating temperature of 200 °C. The improved gas sensing properties were attributed to the porosity of columnar nanostructures and catalytic activities of Pd doping.