Low-frequency noise in CMOS-integrated gas sensors: From a reliability constraint to a selective sensing feature

Low-frequency noise (LFN), often known as flicker noise, considerably impacts semiconductor devices by compromising their stable and reliable operation. In gas sensors, this detrimental impact of LFN is exacerbated by inherently slow sensing dynamics, which amplify interactions between carriers and defects and prolonged gas adsorption-desorption processes. However, although traditionally regarded as an undesirable phenomenon, LFN can yield critical insights into device operation, material properties, and underlying sensing mechanisms, as it directly reflects defects within the sensing materials and the kinetics of gas interactions. Therefore, comprehensive analysis of LFN characteristics is essential for advancing sensor technology and achieving optimized performance, such as signal-to-noise ratio and selectivity. In this study, we systematically investigate LFN characteristics within a complementary metal-oxide-semiconductor (CMOS) integrated sensing platform that uniquely incorporates both n- and p-type field-effect transistors (FETs) and corresponding horizontal floating-gate FET-type gas sensors featuring both various sensing materials (V₂O₅, WO₃, In₂O₃) and structural configurations on a single wafer. Our comprehensive analysis reveals that LFN characteristics are influenced not only by the charge fluctuation on the FET channels but also significantly by interfacial interactions between sensing materials and target gases associated with resistance-capacitance networks stemming from gas reaction. The findings in this study offer critical insights, highlighting that careful optimization and understanding of LFN not only can enhance sensor reliability but also enable selective gas detection through distinctive noise-derived sensing features. This approach has the potential to significantly influence design strategies and operational practices across semiconductor-based sensor technologies.