Low-Power MEMS Gas Sensor Based on TiO ₂ /SnO ₂ Core–Shell Nanorods for Ultrasensitive H ₂ S Detection

In this work, we fabricated a low-power microelectromechanical system (MEMS) gas sensor using TiO 2 /SnO 2 core–shell nanorods for H 2 S detection. The TiO 2 /SnO 2 core–shell nanorods were prepared via a simple hydrothermal method, followed by atomic layer deposition (ALD). The TiO 2 /SnO 2 core–shell material demonstrated significantly improved H 2 S sensing performance compared to pristine TiO 2 nanorods, such as lower operating temperature and higher sensitivity. The optimal response was observed with a SnO 2 shell thickness of 20 nm. At an operating temperature of 300 °C, the optimized TiO 2 /SnO 2 -20 sensor exhibited a response value of 4.5–1 ppm of H 2 S, which is approximately three times higher than that of the pure TiO 2 gas sensor. The significant performance enhancement is primarily attributed to the formation of the TiO 2 /SnO 2 heterojunction, and its underlying mechanism is explained by the heterojunction depletion theory and the chemisorbed oxygen model. Furthermore, the sensor demonstrated excellent linearity, a low detection limit, remarkable stability, and outstanding repeatability. These results confirm that the proposed TiO 2 /SnO 2 core–shell nanorod gas sensor is a promising approach for real-time portable halitosis detection.