FET-type gas sensors: A review

Gas sensing technology is becoming increasingly important in environmental monitoring, medical diagnostics, and industrial safety. Among various types of gas sensors, FET-type gas sensors are increasingly attracting attention due to their miniaturized size, low power consumption, high reliability, and good compatibility with CMOS technology. Therefore, it would be helpful to review how FET-type gas sensors have evolved and how recent trends have been. In this paper, we review the technologies of FET-type gas sensors, focusing on TFT, catalytic metal-gate FET, suspended-gate FET, capacitively-coupled FET, and horizontal floating-gate FET gas sensors. The device structure and operating principle of each type of FET-type gas sensor are explained and then the advantages and disadvantages are discussed. We also review their sensing properties such as sensitivity, selectivity and response/recovery speeds, and the methods to enhance their sensing performances. Finally, we introduce a pre-bias scheme that effectively improves the sensing characteristics of the FET-type gas sensor and its effects, and discuss the key characteristics and development direction of the FET-type gas sensor embedded with a practical low-power micro-heater.