Fast response formaldehyde gas sensor for USN application

Semiconductor type gas sensors based on aluminum-doped zinc oxide with less than 50 nm particle size were fabricated on Si substrate to detect formaldehyde (HCHO) gas existing in building. It is very toxic and pollutant in air and especially, very dangerous for infants and kids. The prepared materials were very fine and uniform and we found out that crystallite sizes were about 10-25 nm through X-ray diffraction analysis and scanning electron microscopy. Gas response characteristics were examined for HCHO gas. In particular, the sensors showed responses to formaldehyde gas at sub ppm (cf, standard of natural environment in building is about 80 ppb), as a function of operating temperatures and gas concentrations. The lowest detection limit is HCHO 25 ppb and response of 800 ppb is about 60% at 350 °C operating temperature. The response time of 8 s to HCHO gas is very fast compared to other commercial products in flow type measurement condition. Repetition measurement was very good with ± 2% in full measurement range.