A new sensing mechanism of Si FET-based gas sensor using pre-bias.

• A new capacitive-type FET (CFET) gas sensor based on Si FET is proposed. • Only five photomasks are used to prepare the CFET sensor and a ZnO thin film prepared by atomic layer deposition (ALD) is adopted as a sensing material. • The NO 2 gas-sensing characteristics are obtained by using pulse pre-bias method. • Depending on the polarity of pre-bias (V pre), the CFET gas sensor exhibits the opposite I D behaviors. • The sensing mechanism is explained by using schematic energy band diagrams. A new capacitive-type FET (CFET) gas sensor is proposed in this work and fabricated by using Si FET technology. Only five photomasks are used to prepare the CFET sensor and a ZnO thin film prepared by atomic layer deposition (ALD) is adopted as a sensing material. A diluted nitrogen dioxide (NO 2) is used as a test gas and the sensing properties of the CFET gas sensor are measured at 180℃ by using pulse pre-bias method. It is verified that the response of the CFET sensor is significantly improved as the absolute value of the difference between pre-bias (V pre) and gate read bias (V rCG) increases. However, the response is negligible when V pre = V rCG. The drain current (I D) of the CFET gas sensor increases by 44.6% at a V pre of −2 V while the I D decreases by 43.2% at a V pre of 2 V under exposure to 0.5 ppm NO 2 at a V rCG of 0 V at 180℃. The response and the recovery times are also investigated. The sensing mechanism is explained by using schematic energy band diagrams. [ABSTRACT FROM AUTHOR]