Influence of the degradation on the surface states and electrical characteristics of EOS structures

The application of ion sensitive field effect transistors (ISFET's) to the measurements of the pH of chemical solutions is one of the most important fields of microelectronic sensors. However, ISFET's still present some problems, such as shifts and drifts of electrical characteristics. In this work a systematic study of the evolution of electrical characteristics of EOS (electrolyte-oxide-semiconductor) and ENOS (electrolyte-nitride-oxide-semiconductor) structures, equivalent to ISFET gates, using the quasi-static C-V method is presented. Results show that the total drift in the flat band voltage can be separated in two terms, one due to immersion in an aqueous ambient and other due to the ionic strength.