Electrolyte-insulator-semiconductor field-effect transistor

A model adapting the surface ionization and complexation of the surface hydroxyl groups on the gate insulator surface in conjunction with the IGFET theory is proposed to arrive at the terminal behavior of the electrolyte-insulator-semiconductor field-effect transistor (EISFET) in response to the variation of electrolyte parameters. Experimental results of EISFET employing thermally grown silicon dioxide in simple electrolytes containing Na
⁺
, K
⁺
and Li
⁺
ions titrated in a pH range from 2 to 9 were found to be in good agreement with the theory. The model successfully explains the pH sensitivity as well as the ion interference effect of the EISFET as a pH sensor. From this model, it is concluded that the surface site density, NS, and the separation of surface ionization constants, in terms of ΔpK, are the main controlling factors for the EISFET as a pH sensor. For high sensitivity and good selectivity, large NS and small ΔpK values are required.