Localized Liquid-Phase Synthesis of Porous SnO₂ Nanotubes on MEMS Platform for Low-Power, High Performance Gas Sensors

We have developed highly sensitive, low-power gas sensors through the novel integration method of porous SnO 2 nanotubes (NTs) on a micro-electro-mechanical-systems (MEMS) platform. As a template material, ZnO nanowires (NWs) were directly synthesized on beam-shaped, suspended microheaters through an in situ localized hydrothermal reaction induced by local thermal energy around the Joule-heated area. Also, the liquid-phase deposition process enabled the formation of a porous SnO 2 thin film on the surface of ZnO NWs and simultaneous etching of the ZnO core, eventually to generate porous SnO 2 NTs. Because of the localized synthesis of SnO 2 NTs on the suspended microheater, very low power for the gas sensor operation (<6 mW) has been realized. Moreover, the sensing performance (e.g., sensitivity and response time) of synthesized SnO 2 NTs was dramatically enhanced compared to that of ZnO NWs. In addition, the sensing performance was further improved by forming SnO 2 –ZnO hybrid nanostructures due to the heterojunction effect.