Modeling the pH response of silicon nitride ISFET devices

Simulations using the site binding theory were carried out considering both the response of buried sites and the surface oxidation of silicon nitride. These non-ideal effects were modelled using simplified functions that influence the site densities of the silicon nitride. The simulations were compared with measurements on electrolyte–insulator–silicon (EIS) structures. The results obtained did show good correspondence between simulations and measurements. Buried sites were found to increase the sensitivity of ISFET devices, in contrary to surface oxidation which causes a decrease of the sensitivity. The time between pH change and measurements has proved to be the most significant factor determining non-linearity and hysteresis of the sensor signal and sensitivity.