Basic properties of the electrolyte—SiO2—Si system: Physical and theoretical aspects

In order to provide an improved understanding of ion-sensitive field-effect transistors (ISFET´s) an analysis of the quasi-equilibrium characteristics of an electrolyte-oxide-semiconductor (EOS) system has been carried out. The characteristics of this system are examined by initially considering two limiting cases. In the first case, an ideal unblocked interface between the electrolyte and the oxide is assumed. Electrochemical processes of ion exchange dominates and consequently, a Nernstian response is experienced. The second limiting case assumes a totally blocked interface such that the behavior of the EOS system is dictated by electrostatic factors. The analysis is then generalized to examine the case of an electrolyte-pyrogenic SiO2-Si system using a site binding model to describe the ionic adsorption processes at the electrolyte-pyrogenic SiO2interface. The C-V characteristics and changes in flat-band voltage of the EOS system in response to pH are examined. Analytical results show that in general, the response does not obey the classical Nernst equation. Correlation of theoretical and experimental results yields excellent agreement suggesting that the models used in this study can provide an adequate description of the physical processes.