Enhancement of CO sensitivity of indium oxide-based semiconductor gas sensor through ultra-thin cobalt adsorption

An In2O3-based thin film sensor was fabricated on alumina substrate for detecting CO gas and ultra-thin transition metal Co was adsorbed by sputtering and annealed as a surface activator as thick as 0.7-2.4 nm to enhance its sensitivity (S). As the thickness W of Co catalyst layer increased, the sensitivity of Co-In2O3 Sensor for show the highest sensitivity of S = 7.5 at t = 2.1 run at 350 degreesC. For the comparison, C3H8 was used as a test gas of hydrocarbon contained gas and the maximum sensitivity for 1000 PPM C3H8 was S = 13.5 at t = 1.4 mn at 400 degreesC. In consequence, it was found the possibility that CO and C3H8 can be detected without cross-talking by using hybrid type Co-In2O3 sensor. From X-ray photoelectron spectroscopy, adsorbed Co layer was oxidized Coo after 500 degreesC annealing in air and to be covered with Co3O4. Such a formation of Coo (p-type)-In2O3 (n-type) junction was suggested as a main sensing mechanism to explain the enhanced sensitivity of Co-In-In2O3 sensor. (C) 2001 Elsevier Science B.V. All rights reserved.