Fabrication of ISFET for pH detection

Abstract

The ability to detect variation of pH from the changes ions concentration has gained Ion Sensitive Field Effect Transistor (ISFET) huge interest in various fields such as environmental monitoring in agricultural sector and water quality control. The advantages of using ISFET for pH detection are such as its small size, robustness, label free, low output impedance and rapid response. Researchers have attempted to fabricate ISFET using silicon oxide as the sensing membrane that is responsible for ion detection. In this paper, the silicon nitride (Si3N4) is used instead to replace silicon oxide as the sensing membrane to enhance the stability and sensitivity. For the analysis of ISFET in test solution, the Ag/AgCl electrode is used as the reference electrode and pH buffer solution of each basic pH value are used in the ISFET analysis. However, the results generated by LabTracer 2.0 measurement system have shown that ignorance to take pre-cleaning steps will lead to unevenly coated sensing membrane layer hence causing the device to malfunction. Therefore, pre-cleaning steps for wafer fabrication of any devices is very crucial to produce a good device.