Tellurium sputtered thin films as NO2 gas sensors

Tellurium thin films were deposited onto glass and alumina substrates by an rf sputtering system for NO2 gas sensor applications. The surface morphology and structure of the deposited films were investigated by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. As the thickness of the film was increased from 100 to 300 nm the morphology of films changed from a smooth amorphous to polycrystalline nature. The NO2 gas-sensing properties were determined by measurement of the resistance variation of the films as a function of working temperature and gas concentration. Gas sensitivity was largely influenced by the surface morphology of the films. The films with a thickness of 300 nm deposited on a glass substrate showed the maximum response to NO2 at room temperature. Response and recovery times, reproducibility and long-term stability of these films were also investigated.