Enhanced Nitrogen Dioxide Gas-Sensing Performance Using Tantalum Pentoxide-Alloyed Indium Oxide Sensing Membrane

In this paper, various tantalum pentoxide-alloyed indium oxide (Ta:In₂O₃) films were deposited on quartz substrates as the sensing membranes of nitrogen dioxide (NO₂) gas sensors using a radio-frequency (RF) magnetron co-sputte-ring system. Using an energy-dispersive spectrometer (EDS), the Ta content in the deposited Ta:In₂O₃ films was 0, 1.28, 2.33, and 2.98 at.% corresponded to the RF power of 0, 30.0, 37.5, and 45.0 W applied to the tantalum pentoxide (Ta₂O₅) target, respectively. The grain size of the Ta:In₂O₃ films calculated from the X-ray diffraction (XRD) results was reduced from 9.9 to 7.6 nm as the Ta content of the Ta:In₂O₃ films increased from 0 to 2.98 at.%. The associated electron concentration increased from 1.9times 10-{16} cm -{-3} to 1.0times 10-{18} cm -{-3} by increasing the Ta content from 0 to 2.33 at.%. Compared with the indium oxide (In₂O₃) gas sensors, since the Ta:In₂O₃ sensing membrane with the Ta content of 2.33 at.% had the lowest activation energy of 0.39 eV, its responsivity was enhanced from 29.8 to 64.5 and the operation temperature was decreased from 150 °C to 120 °C under a NO₂ concentration of 100 ppm. Under a NO₂ concentration of 100 ppm at an operation temperature of 120 °C, the associated response time and recovery time of the Ta:In₂O₃ gas sensor with a Ta content of 2.33 at.% were improved to 59 and 339 s, respectively.