Study of sputtered ZnO-Pd thin films as solid state H2 and NH3 gas sensors

ZnO thin films have been prepared by an r.f. sputtering technique. After coating the ZnO surface with a thin discontinuous Pd film, the structure has been used as a gas sensor element for H 2 and NH 3 gases. The electrical resistance of the sensor changes under H2 or NH3 ambient gas and, before a saturation value is reached, the resistance vs. time curve shows peculiar features with a particular negative characteristic. Gas-sensing properties of the sensor show that the sensor is highly sensitive to H2 and selective between H2 and NH3 and that its response time is in the range of a few seconds. When the H2 or NH3 ambient gas is restored to its initial composition, the change in electrical resistance of the sensor is reversible at elevated temperatures under N2 ambient and the presence of 0 2 is not needed to obtain reversi bili l y.