Micro-heater embedded ISFET pH sensor with high-k gate dielectrics for enhanced sensitivity

The measurement of pH is an important routine practice in many chemical and biomedical applications. This work reports the design of a pH sensor based on the Ion Sensitive Field Effect Transistor (ISFET). The COMSOL Multiphysics (R) platform has been used to model and simulate the pH sensor in three dimensions (3D) while combining heat transport, electrostatic, and semiconductor modules. The binding of ions in gate dielectrics results in induced charge carriers in the conducting channel of 3D ISFET, which is controlled by the applied gate voltage for determining ion concentration. Here, the pH of water as the bulk electrolyte is measured by attaining the required gate voltage to achieve a certain drain current in 3D ISFET. The pH sensitivity of 3D ISFET with different high-k gate dielectrics such as Ta2O5, Al2O3, HfO2, ZrO2, and SiO2 is measured and compared. The 3D ISFET with Ta2O5 exhibited excellent sensitivity of 59.0 mV pH-1 with a wide linear detection range of pH from 1 to 13 at room temperature compared to other high-k gate dielectrics. Furthermore, the sensitivity was further enhanced to 66.0 mV pH-1 at 60 degrees C due to the incorporation of a micro-heater into the ISFET. The excellent sensitivity and wide linear detection range can be attributed to the high concentration of surface sites in the Ta2O5 sensing film and improved disassociation constants in the presence of the gate dielectric in contact with the electrolyte. Finally, this sensor demonstrates its potential for real applications.