A fully CMOS-integrated pH-ISFET interface circuit

ISFET is a potentiometric sensor that is easily adapted for a wide range of chemical, biochemical and biomedical measurements. This article presents an ISFET sensor system-on-chip including the ISFET/REFET (Reference FET) pair and ISFET/REFET amplifiers, bias current generator, as well as a reference electrode structure, all integrated on the same chip based on CMOS technology. The sensor chip is fabricated in a standard 0.35 mu m 4-metal and 2-poly layer CMOS process (Chartered Semiconductor) to which extra post processing steps are added for depositing membranes. The chip operates at 3.3V and the total die area is 5 mm(2). Finally the performance of the integrated sensor interface circuit is measured and analyzed.