Ultrasensitive Coplanar Dual-Gate ISFETs for Point-of-Care Biomedical Applications

The sensitivity of conventional ion-sensitive field-effect transistors (ISFETs) is limited by the Nernst equation, which is not sufficient for detecting weak biological signals. In this study, we propose a silicon-on-insulator-based coplanar dual-gate (Cop-DG) ISFET pH sensor, which exhibits better performance than the conventional ISFET pH sensor. The Cop-DG ISFETs employ a Cop-DG consisting of a control gate (CG) and a sensing gate (SG) with a common gate oxide and an electrically isolated floating gate (FG). As CG and SG are capacitively coupled to FG, both these gates can efficiently modulate the conductance of the FET channel. The advantage of the proposed sensor is its ability to amplify the sensitivity effectively according to the capacitive coupling ratio between FG and coplanar gates (SG and CG), which is determined by the area of SG and CG. We obtained the pH sensitivity of 304.12 mV/pH, which is significantly larger than that of the conventional ISFET sensor (59.15 mV/pH, at 25 °C). In addition, we measured the hysteresis and drift effects to ensure the stability and reliability of the sensor. Owing to its simple structure, cost-effectiveness, and excellent sensitivity and reliability, we believe that the Cop-DG ISFET sensor provides a promising point-of-care biomedical applications.