RADIO-FREQUENCY MAGNETRON SPUTTERING GROWTH AND CHARACTERIZATION OF INDIUM TIN OXIDE (ITO) THIN-FILMS FOR NO2 GAS SENSORS

A thin-film indium-tin oxide (ITO) NO//2 sensor has been fabricated by radio frequency magnetron sputtering (RFMS) from a target of a mixture of In//2O//3 and SnO//2 in the proportion 9:1 by weight. The detection of NO//2 gas is carried out by measurement of electrical resistivity changes induced in the ITO thin film by gas chemisorption on the solid surface. Such sensors have shown good long-term stability and high sensitivity to NO//2 at concentrations between 2-3 ppm in air at an operating temperature of 200 degree C, while they are not sensitive to high concentrations of interfering gases such as CO and CH//4. The sensor response time is less than 0. 7 s, while its recovery time is 1-2 min at an operating temperature at 300 degree C. A simple electronic theory of chemisorption, based on two donor levels at 0. 12 eV and 0. 38 eV respectively, has been used to give a possible explanation of the sensor selectivity.