Modelling of reference electrode for a SÌ3N4 gate pH ISFET

Abstract

Ion sensitive field effect transistor (ISFET), which is a modification of metal oxide semiconductor field effect transistor, is a successor of the glass pH electrode. Since its inception over the four decades and beyond, it has witnessed a growing demand in various fields such as medical, food safety, military, waste water management etc. Proper positioning of the reference electrode in an ISFET device is very essential for the pH measurement process. In this work, a model for proper positioning of reference electrode with respect to the SÌ3N4 sensing surface of an ion sensitive field effect transistor has been developed. The model has been simulated in MATLAB simulation environment. The simulation results show that obtaining unambiguous reading is possible only when the reference electrode is placed more than the three times of the debye length of the electrolyte solution. This also gives an idea about the overall size of the measurement system.