Analysis of the Response of Ion Sensing FETs with a Chemically Modified Gate Insulator

Abstract

This paper is devoted to the analysis of the physicochemical parameters influencing the response of ion sensing FETs obtained by chemical grafting of the silica gate insulator. The site binding theory has been applied to the modified silica/electrolyte interface; for the first time the equilibria involving H⁺ and M⁺ ions have been taken into account. The established theoretical expression shows that the sensitivity of the ion sensing FETs is better when the number of sensitive sites and the complexation constant of these sites are higher. The experimental response of the Ag⁺ sensing ISFET was fitted with this model. The percentage of cyanografted sites is determined to be 8%; their complexation constant is −0.9.