Optimization of channel structure and bias condition for signal-to-noise ratio improvement in Si-based FET-type gas sensor with horizontal floating-gate

Abstract

© 2022 Elsevier B.V.Sensing performances of the Si-based field-effect transistor (FET)-type gas sensor are not only affected by sensing material characteristics but also by electrical properties of a transducer. Therefore, the optimization of transducer properties, including subthreshold swing, transconductance, and low-frequency noise (LFN) characteristics, is necessary for improving the sensing performances. In this paper, NO2 gas sensing properties, LFN characteristics, and signal-to-noise ratio (SNR) of the FET-type gas sensor having different channel structures (surface and buried channel FETs) are investigated. An n-type indium-gallium-zinc oxide (IGZO) thin-film is used as a sensing layer. The LFN characteristics of both sensors are explained using a carrier number fluctuation model with correlated mobility fluctuation. The flat-band voltage fluctuation (SVfb) value of the buried channel (4.54×10−10 V2/Hz) is smaller than that of the surface channel (2.73×10−9 V2/Hz). Thus, the SNR of the sensor with a buried channel shows ~10 times larger SNR than that with a surface channel. Also, the optimal bias conditions for both sensors are suggested. The sensor with buried channel FET has a limit of detection (LOD) of 44.2 ppt to NO2 gas.