Modeling of Ion Sensitive Field Effect Transistor for Sensing Application using TCAD

Hydrogen ion concentration (pH) of a solution can be measured using FET type sensor called Ion sensitive field effect transistor, ISFET. Chemical reactions occur at the electrolyte – insulator interface making the FET sensitive to pH. The objective of this work is to model the electrolyte-insulator structure of a transistor using Silvaco TCAD tool. Sensitivity is measured based on the shift in the threshold voltage which is caused by the effect of pH on the charge and the potential distributions in the gate insulator. Based on the analytical calculation of parameters of the electrolyte region, semiconductor materials are used to model the reference electrode and electrolyte. In this study, Silicon Nitride and Aluminum Oxide are used as gate insulators for ISFET and their performance comparison is made for sensing applications. The transfer and output characteristics of the transistor are obtained by simulation for both the films for various thicknesses. A comparison of the effect of thickness of films on device performance is analyzed since the dielectric constant of Aluminum oxide is higher than Silicon nitride.