Modeling H/sup +/-sensitive FETs with SPICE

A generalized physical model including two kinds of binding sites is presented on H/sup +/-sensitive ISFET devices. The model results in a set of equations which is introduced into a modified version of the electronic circuit simulation program SPICE. In this way, the effects induced on the device performances by varying several physico-chemical parameters are analyzed. The slope of V/sub out/ versus pH curves is predicted for SiO/sub 2/-, Al/sub 2/O/sub 3/-, and Si/sub 3/N/sub 4/-gate ISFETs. The model is then used to predict the behavior of a hypothetical, partially pH-insensitive (REFET) structure. Finally, the model is utilized to fit the slow response of the Al/sub 2/O/sub 3/-gate ISFET to a pH stop.<
>