ISFET sensor coupled with CMOS read-out circuit microsystem

The development of a prototype microsystem for measuring the pH, i.e. H+ ion concentration, of an aqueous electrolytic solution is described which has a resolution higher than 1/20 of pH. The microsystem is composed of an ion sensitive field effect transistor (ISFET) sensor coupled with a CMOS read-out channel capable of providing a low-impedance analogue output and protection against electrostatic discharges. The silicon integrated ISFET sensor chip and the CMOS read-out chip have been fabricated, packaged and successfully tested at the IRST-Microsystem Division of Trento (Italy) using the internal microfabrication facility.