Enhanced pH Sensitivity of ISFET via TiO₂ Gate Doping: A Novel Approach

This paper presents the simulation and analysis of an Ion-Sensitive Field-Effect Transistor (ISFET)-based pH sensor designed for accurate detection of ion concentrations through variations in gate voltage. The ISFET structure replaces the conventional gate of a MOSFET with an electrolyte and titanium dioxide (TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>) doping, enabling the sensing of pH levels via ion-gate dielectric interactions. In this study, potassium chloride (KCl) is used as the electrolyte, and its influence on the ISFET’s electrical behavior is systematically analyzed. The output characteristics, including the drain current (I<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</inf>) versus drain-source voltage (V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds</inf>) under varying gate-source voltages (V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gs</inf>), are obtained using COMSOL simulation. The semiconductor and electrolyte models are meticulously coupled to ensure a realistic representation, capturing the ion-sensitive interface’s behavior. A simplified global equation technique is employed to derive critical operating parameters efficiently, without explicitly modeling the feedback circuitry. The ISFET’s performance is further evaluated by analyzing its sensitivity to pH variations and extracting relevant electrical characteristics for optimization. This work provides a comprehensive approach to simulating ISFET-based pH sensors, highlighting its potential for efficient and precise pH measurement in biochemical and industrial applications.