Study of ISFET for KCl sensing

This work presents the fabrication and electrical characterization of the Ion Sensitive Field Effect Transistor (ISFET) exposed to potassium chloride (KCl) solutions. The focus of the study is to compare two measurements methods and verify the effects of these methods in the device threshold voltage (V_TH) sensitivity to the different KCl concentrations. First, a reference electrode (a platinum needle) is placed in the sample solution over the gate area of the device, demonstrating that the threshold voltage decreases with the increase of the KCl concentration. The method shows a sensitivity of 10.44 mV/mM for the low KCl concentration range (0 to 10 mM) and 0.5 mV/mM for the higher KCl concentration range (10 to 100 mM). The second method involves inserting a second platinum electrode into the solution on the field oxide. This method proposes the KCl electrolysis to increase the selectivity for potassium ions. The result allows the next steps for potassium sensing biosensor application with selective membranes.