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 μm, 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.