High-Performance SnO2 Ink for Detecting Low-Temperature H2S Gas with Advanced Dispensing Printing Technology

Hydrogen sulfide (H2S) is a highly toxic and environmentally hazardous gas, necessitating sensitive and reliable detection at trace concentrations. In this study, a dispensing-printed SnO2-based MEMS gas sensor was developed using a sol–gel-derived SnO2 precursor ink deposited directly onto a Pt-interdigitated micro-hotplate. The precursor ink was optimized for dispensing printing and subsequently annealed at 450 °C to produce a crystalline SnO2 sensing layer. XRD and FTIR analyses confirmed the formation of crystalline tetragonal rutile SnO2 and characteristic Sn–O bonding, while FE-SEM revealed an interconnected particulate sensing morphology with well-distributed Sn and O. XPS further confirmed the predominant Sn4+ chemical state and the presence of lattice and surface-related oxygen species, which are beneficial for gas adsorption and surface reactions. The fabricated sensor demonstrated effective H2S sensing performance at a relatively low operating temperature of 90 °C. The response increased systematically with the H2S concentration from 10 to 100 ppb, reaching a maximum response of 3.8897 at 100 ppb. A sensitivity of 0.0282 response units per ppb was obtained from the calibration curve, demonstrating a strong concentration-dependent response in the investigated range. Additionally, the power consumption of the sensor was low (~32 mW); the sensor also exhibited a response time of approximately 153 s, although recovery was comparatively slower at approximately 277 s at 30 ppb. Furthermore, the sensor showed a substantially higher response to H2S than the investigated interfering gases, including H2, NH3, NO2, and CO. These results demonstrate that the integration of dispensing-printed SnO2 with a MEMS micro-hotplate provides a promising route toward low-temperature, miniaturized, and highly sensitive trace-level H2S sensing.