Recent advances on H2 sensor technologies based on MOX and FET devices: A review

The importance of metal oxide semiconductor (MOX) and field effect transistor (FET) based sensors has been increasing due to their extended practical applications for gas detection. Various investigations have confirmed that gas sensing characteristics depend on the sensitivity of the metal oxide and catalytic materials. In recent years, hydrogen gas sensor technology has been progressively more capable in practical applications. The propagation velocity of hydrogen flames is high enough to cause severe explosion over an extensive range of 4%-75% H2. Therefore, the use of hydrogen carries a great risk, and the requirement for its leakage detection is imperative in hydrogen generation, transportation, stockpiling, and its utilization. Usage of MOX and FETs has increased tremendously in designing precise hydrogen sensors. Therefore, in this review, the authors have focused on the recent development in MOX and FET based hydrogen sensors. MOX sensors are most widely available as commercialized ones.Also, FET-type gas sensors have many advantages, compared with traditional ones owing to their reduced shape, size, and lower production cost. Nevertheless, the processing parameters and reproducibility need to be enhanced for expanding their applications. In this review, the role of the important sensing parameters, e.g., measurement range, sensitivity, selectivity, response and recovery time, on the sensing mechanism and operation, and the most recent innovation and improvement in MOX and FET sensing technologies are discussed. Finally, we report the sensing techniques, mechanism and factors affecting the sensitivity for MOX and MOSFET type sensors.