$NO_2$ gas sensors for environment monitoring using 1㎜×1.2㎜ device with Pt heater and Au electrode were fabricated by screen-printing method and $NO_2$ sensing characteristics of sensing materials were tested. $NO_2$ sensing materials were $WO_3$, $WO_3$-3wt%ITO, $WO_3$-3wt%$In_2O_3$ and $In_2O_3$-3wt%$WO_3$.
$WO_3$-3wt%ITO and $WO_3$-3wt%$In_2O_3$ showed unstable $R_{gas}$ because of high $R_{air}$. When operating temperature was about 315℃, $WO_3$ and $In_2O_3$-3wt%$WO_3$ sintered at 700℃ had high sensitivities to $NO_2$, fast response & recovery time and high selectivities to $H_2$ 928ppm, CO 500ppm and $C_2H_5OH$ 85ppm.
Especially, $WO_3$ and $In_2O_3$-3wt%$WO_3$ were suited for $NO_2$ sensing material for environment monitoring because the sensitivities to $NO_2$ 1ppm of these were 2.6 and 4.5 respectively.
