Non-glass, solid-state, pH microsensor : ion-sensitive field-effect transistor (ISFET)

Abstract

pH, a measure of the hydronium ion (H₃O+) concentration, and indicator of acidity or alkalinity of a solution, is a common analytical parameter. The pH of food and drink affects its taste, the pH of medicine determines its effectiveness and the pH of dye affects the colour and uptake of dye by the fabric. The glass pH electrode has been accepted in the standard industrial workhorse tool for pH measurements.Ion-sensitive field-effect transistor (ISFET) is a microelectronic device in which the hydronium ion concentration in the solution produces agate potential modulating the electric charge carrier flow between the source and drain terminals. The present paper describes the fabrication of ISFET, starting with P-type silicon wafer and up to the packaging stage. In addition, current-voltage characteristics of MOSFET test devices simultaneously fabricated on the wafer have been plotted. pH-sensitivity of developed ISFET was found to be 50 mV/pH.