Ultralow detection limit MEMS hydrogen sensor based on SnO2 with oxygen vacancies

Controllable and efficient construction of oxygen vacancies on the surface of metal oxide semiconductors (MOSs) is essential for their application in the gas sensor. Herein, a general H2 reduction method is developed to synthesize SnO2 with oxygen vacancies defect (SnO2-D) by annealing the SnO2 in a H2 atmosphere at different temperature (300 °C, 400 °C and 500 °C), and then named SnO2-D3, SnO2-D4 and SnO2-D5, respectively. It was found that although the determined specific surface areas for pristine SnO2, SnO2-D3, SnO2-D4 and SnO2-D5 are 103.749 m2g−1, 63.316 m2g−1, 47.652 m2g−1 and 15.541 m2g−1, respectively, the gas sensitivity test results indicate that the SnO2-D4 Micro-Electro-Mechanical System (MEMS) sensor shows improved response and excellent low-concentration detection capability (down to 0.1 ppm) to H2 compared with that fabricated with pristine SnO2, SnO2-D3 and SnO2-D5. The abnormal relationship between specific surface area and gas sensing performance is attributed to the more oxygen vacancies of SnO2-D4 surface. In addition, ZnO (ZnO-D) and In2O3 (In2O3-D) with oxygen vacancy defects based on the H2 reduction method show better gas sensitivity than ZnO and In2O3 sensors, which further proves that oxygen vacancy defects can effectively improve the gas-sensing performance of MOSs.