Comparative Study of Field Effect Transistor Based Biosensors

A comparative study of biosensors based on a field effect transistor (FET) configuration is conducted using numerical analysis. A conventional back-gated device and three different nanogap-based structures are evaluated in terms of their performance metrics including response, sensitivity, detection limit, and dynamic range. An electrostatic model is used to address the sensing principle. The biochemical reaction is emulated simply by a change in the negative charge density and permittivity. The back-gated silicon nanoribbon FET (SiNR-FET) is used as a reference for comparison. The SiNR-FET is not affected by the permittivity change due to the biochemical reaction, whereas other nanogap-based structures are influenced by both the charge density and the permittivity shifts. Among the nanogap-based structures, a dielectric modulated FET (DM-FET) exhibits the widest dynamic range and a strong permittivity dependency. An underlap gate FET (UG-FET) and a fingered gate FET (FG-FET) show the highest sensitivity and detection limit. But the dynamic ranges of the UG-FET and FG-FET are narrower than that of the DM-FET. Nevertheless, by the nature of independent controllability of two gates, the FG-FET allows a tunable dynamic range. This comparative study offers application-specific guidelines for making appropriate choices for the sensor structure.