Modeling ISFET microsensor and ISFET-based microsystems: a review

Silicon technology is one of the most promising for sensor development. Moreover, electronic simulation tools, originally introduced to design electronic circuits, can be adapted to design silicon-based chemical- and bio-sensors. These considerations lead to the description of the models we developed and implemented in the program SPICE for simulating ion-sensitive field-effect transistors (ISFETs) and ISFET-based microsystems. The implementation in SPICE and the simulation results are described in terms of each model. In particular, a new model of a Si3N4-gate ISFET operating under subthreshold conditions and the related electrochemical characterization are presented. The ISFET models were then used to develop a CAD system that can be considered as a general-purpose tool for designing integrated ISFET-based sensors and microsystems with on-chip processing and control capabilities.