Metal oxide thin film materials, including SnO2, TiO2, WO3, MoO3, ZnO, have been widely studied for gas sensing applications. However, new gas-sensing materials with distinct and diverse characteristics for new sensing applications such as electronic nose are still being explored. Presently, gas sensing properties of other metal oxides have not yet been extensively explored. Chromium oxide is an interesting metal oxide for gas sensor because of its temperature stability and moderate electrical conductivity. Nevertheless, there have been very few studies on gas sensing behaviors of this material. In this work, chromium oxide thin films were systematically studied by reactive sputtering with varying sputtering parameter including oxygen flow rate. Structural characterization by means of scanning electron microscopy and X-ray diffraction reveals that the films have sub-micometer grain-size with Rhombohedral phase of Cr2O3. Gas-sensing performances of sputtered chromium oxide thin film have been characterized toward ethanol and acetylene sensing. It was found that chromium oxide thin films exhibit p-type conductivity with increased resistance when exposed to ethanol and acetylene, which are reducing gases. In addition, sensitivity to both acetylene and ethanol tend to improve as oxygen flow rate increases. Furthermore, the chromium oxide thin films exhibit high sensitivity at moderate temperature of 250-300 °C with minimum operating temperature of 200 °C.
Synthesis and Characterization of Copper Doped Zinc Oxide Thin Films for CO Gas Sensing