Biosensor Based on Ion-Sensitive Nanowire Field-Effect Transistor Using the Minimum Contact to the Floating Gate

The ion-sensitive field effect transistor (ISFET) is a promising tool for detecting intermolecular interactions, including biochemical ones. Using the ISFET, it is possible to recognize various mechanisms of specifically adsorbed substances. In addition, ISFET can be integrated with CMOS technology, which opens up new prospects for creating intelligent micro- and nanosystems. In this study, the influence of the design and technological parameters of the ISFET on charge sensitivity is investigated using numerical simulation. Two types of the ISFET design based on a completely depleted floating-gate SOI structure are presented. The designs differ by the way of forming the liquid medium–gate contact. The analytical dependences of the charge sensitivity of the ISFET, which make it possible to analyze the ISFET sensitivity, are obtained. It is shown that the limiting sensitivity is achievable on a composite nanowire structure with submicron dimensions. The sensitivity of the considered ISFET design with the characteristic size of 1.2 µm when an analyte is adsorbed is about 50 effective electron charges. The ISFET designed with submicron physical dimensions (wire width of 10 nm and wire length of 100 nm) has the sensitivity of 1 to 2 effective electron charges.