Low temperature inkjet-printed metal oxide sensors for sensitive and selective NO₂ detection

Advancements in gas sensor technology are critical for enhancing environmental monitoring and pollution control systems. Among the various sensor types, inkjet-printed gas sensors have emerged as a promising solution due to their low fabrication cost, scalable production, and compatibility with modern electronics. This study presents the development and characterization of inkjet-printed chemiresistive gas microsensors based on tin oxide (SnO₂) and indium oxide (In₂O₃) for the detection of nitrogen dioxide (NO₂), a major air pollutant associated with vehicular emissions and industrial activities. The sensors were fabricated on compact CMOS-compatible microchips, with integrated microheaters and electrodes measuring less than 250 × 250 microm, enabling miniaturization and potential on-chip integration for portable sensing platforms. Metal oxide sols were deposited using a precise inkjet printing technique, and crystallization of the sensing layers was achieved via localized heating through the integrated microheaters. The SnO₂ sensor demonstrated excellent sensitivity at room temperature, detecting NO₂ concentrations as low as 10 ppb, while the In₂O₃ sensor showed optimal performance at 100 °C with comparable detection limits. Both sensors exhibited linear response behavior over a range of NO₂ concentrations, along with strong selectivity against common interfering gases. Although humidity induced minor fluctuations, both sensors maintained robust NO₂ selectivity. These results underscore the potential of inkjet-printed metal oxide microsensors for developing compact, low-power, and highly sensitive gas detection systems.