Modeling and simulation of electrolyte pH change in conventional ISFET using commercial Silvaco TCAD

Abstract

This paper proposes a numerical simulation approach to study the electrolyte pH change of ion-sensitive field effect transistor (ISFET) structures using Silvaco technology computer-aided design (TCAD) tools. This paper examines the ISFET device's electrical response to electrolyte pH change. The modeling method is exploited by changing the potential surface charge depending on the electrolyte pH change and investigating how will it cause threshold voltage shift of ISFET device and other transfer characteristic parameters. The properties of a user-defined material offered by Silvaco are exploited to simulate the electrolyte behavior. The parameters of silicon semiconductor material (i.e., energy bandgap, permittivity, affinity, and density of states) are set to reconstruct an electrolyte solution. The electrostatic solution of the electrolyte area is investigated by giving a numerical solution for the semiconductor equation inside this area. Results show excellent agreement between theoretical model and self-consistency TCAD model. Additionally, transfer characteristics of a conventional ISFET device are simulated. The ID current as a function of the reference voltage VRef. and drain voltage VD for different pH scale and ID current as a function of VDS for different VRef. values for specific pH value are simulated. The proposed model allows accurate and efficient ISFET modeling by trying different designs and further optimization with commercial Silvaco TCAD tools rather than expensive fabrication.