A generalized theory of an electrolyte-insulator-semiconductor field-effect transistor

A model of surface ionization and complexation of surface hydroxyl groups on the gate insulator surface is adapted in conjunction with electronic device physics to arrive at a generalized theory for the current-voltage characteristics of an electrolyte-insulator-semiconductor field-effect transistor (EISFET) in electrolyte solutions. EISFET's that employ thermally grown silicon dioxide were tested in simple electrolytes that contain Na+, K+, and Li+ions titrated in apH range from 2 to 9. Experimental results show good agreement with the theory. The model successfully explainspH sensitivity, as well as the ion interference effect, of the EISFET working as apH sensor. From this model, it is conluded that, among all the electrolyte parameters associated with an EISFET, the surface site density of the hydroxyl groups Nsand the separation of surface ionization constantsΔ pKare the primary factors to consider when employing EISFET's aspH sensors. For high sensitivity and good selectivity, large Nsand smallΔ pKvalues are required.