Abstract
An In 2O 3-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 ( t) of Co catalyst layer increased, the sensitivity of Co–In 2O 3 sensor for show the highest sensitivity of S=7.5 at t=2.1 nm at 350°C. For the comparison, C 3H 8 was used as a test gas of hydrocarbon contained gas and the maximum sensitivity for 1000 ppm C 3H 8 was S=13.5 at t=1.4 nm at 400°C. In consequence, it was found the possibility that CO and C 3H 8 can be detected without cross-talking by using hybrid type Co–In 2O 3 sensor. From X-ray photoelectron spectroscopy, adsorbed Co layer was oxidized CoO after 500°C annealing in air and to be covered with Co 3O 4. Such a formation of CoO (p-type)–In 2O 3 (n-type) junction was suggested as a main sensing mechanism to explain the enhanced sensitivity of Co–In 2O 3 sensor.
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