CMOS ISFET microsystem for biomedical applications

The development of a novel differential readout architecture for CMOS ion-sensitive field-effect transistor-based (ISFETs) microsystems is described. The ISFETs are fabricated using a standard CMOS process. A differential measurement between two ISFET operational transconductance amplifiers (IOTAs), and a gold wire as a pseudo reference electrode, is used to monitor pH changes. Specifically, these two IOTAs have different pH sensitivities, a function of the size of two MOSFETs in the two IOTAs. The microsystem uses silicon nitride (Si₃N₄) as the pH sensitive layer and has a sensitivity of 40-45 mV/pH. The ISFET layout uses an extended gate approach that reduces leakage, drift and packaging constraints. The microsystem provides a low cost, low power and disposable pH monitoring platform for biomedical applications