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 TiO2/SnO2 core–shell nanorods for H2S detection. The TiO2/SnO2 core–shell nanorods were prepared via a simple hydrothermal method, followed by atomic layer deposition (ALD). The TiO2/SnO2 core–shell material demonstrated significantly improved H2S sensing performance compared to pristine TiO2 nanorods, such as lower operating temperature and higher sensitivity. The optimal response was observed with a SnO2 shell thickness of 20 nm. At an operating temperature of 300 °C, the optimized TiO2/SnO2-20 sensor exhibited a response value of 4.5–1 ppm of H2S, which is approximately three times higher than that of the pure TiO2 gas sensor. The significant performance enhancement is primarily attributed to the formation of the TiO2/SnO2 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 TiO2/SnO2 core–shell nanorod gas sensor is a promising approach for real-time portable halitosis detection.