Study of the working of ion sensitive F.E.T.

C(V) and G(V) measurements have been performed on ion-sensitive devices (having a SiO2membrane) and exhibiting a non nerstian sensitiveness of 34 mV/pH in an aqueous solution. We show that the density of interface states increases during the immersion of the device. The analysis of the results allows us to suppose that the reversibility and the reproducibility shown by the ISFETs is due to the sensitiveness of the threshold voltage of the device to the voltage drop across the Helmholtz layer. This voltage drop should be not nernstian. Besides the interface states due to the liquid as well as their evolution during the working of the device seem to not have any influence to its sensitiveness measured on their threshold voltage.