pH ISFET Stabilization Time Measurement Analysis and Its Readout and Control Circuit

Ion sensitive field effect transistors (ISFET) is used to measure ion concentration in liquid solutions. An ISFET that is used to measure ion concentration in liquid solutions for the first time, requires certain amount of time before actual measurements can be realized. This amount of time is called stabilization time. Typically, this stabilization time varies with external conditions such as type and conditions of the solution under test and performance of the ISFET sensors. The aim of the study is to determine stability criterion to automatically determine the stabilization time of ISFET sensors by utilizing a readout and control circuit and microcontroller. Our results show that the stabilization time of sensors used is about 50 to 60 seconds. The authors have tested commercial Ta2O5 pH ISFET sensors. In the future the authors wish to analyze other ions as well.