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.