Sensing mechanism of hydrogen gas sensor based on RF-sputtered ZnO thin films

The mechanism of hydrogen (H₂) gas sensing in the range of 200–1000 ppm of RF-sputtered ZnO films was studied. The I–V characteristics as a function of operating temperature proved the ohmic behaviour of the contacts to the sensor. The complex impedance spectrum (IS) of the ZnO films showed a single semicircle with shrinkage in the diameter as the temperature increased. The best fitting of these data proved that the device structure can be modelled as a single resistance-capacitance equivalent circuit. It was suggested that the conductivity mechanism in the ZnO sensor is controlled by surface reaction. The impedance spectrum also exhibited a decreased in semicircle radius as the hydrogen concentration was increased in the range from 200 ppm to 1000 ppm.