Carrier gas dynamics-driven defect engineering of SnO₂ thin films formed by powder aerosol deposition for high-performance hydrogen sensing

Hydrogen is a promising clean energy carrier, but its high flammability requires reliable sensors for early leak detection. Here, Pd-modified SnO₂ thin-film hydrogen sensors were fabricated by powder aerosol deposition (PAD), and the effects of carrier gas, deposition stage, Pd loading, and operating temperature were systematically investigated. By comparing He and Ar gases under the same PAD configuration and injection flow rate, we show that carrier gas-dependent deposition conditions, including gas transport behavior and the resulting steady working-pressure characteristics, govern particle transport, film growth, and near-surface defect chemistry during deposition, thereby determining the final sensing performance. Although rutile SnO₂ nanocrystalline films were produced using both gases, Ar enabled more stable film growth, higher deposition efficiency, and a more favorable defect-related oxygen environment. As a result, the sample deposited in Ar using a single scan exhibited the best overall performance after modification with a 3 nm Pd layer. At 150 °C, this sample delivered a response of 4.93 × 10⁵ toward 2 vol% H₂/air with a response time of 1.19 s, and it showed reliable quantitative detection over 10–20,000 ppm with R² = 0.987. Clear response signals were maintained down to 2 ppm, together with good repeatability, high selectivity, acceptable humidity tolerance, and stable operation over 30 days. This work establishes a process–structure–defect–property relationship in PAD-derived SnO₂ films and provides a mechanism-guided strategy for scalable fabrication of high-performance oxide thin-film hydrogen sensors.