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

Abstract

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 (NO2) 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 (Vpre) and gate read bias (VrCG) increases. However, the response is negligible when Vpre = VrCG. The drain current (ID) of the CFET gas sensor increases by 44.6% at a Vpre of −2 V while the ID decreases by 43.2% at a Vpre of 2 V under exposure to 0.5 ppm NO2 at a VrCG 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.