Ion-Sensing Devices with Silicon Nitride and Borosilicate Grlass Insulators

Ion-sensitive field-effect transistors (ISFET's) with silicon dioxide, silicon nitride, and borosilicate glass as the active gate material were fabricated and tested for pH-sensiag applications. The borosilicate glass and silicon nitride devices were found to have a linear potential /pH response and previous theories of ISFET function were inadequate to explain this. A two-site theory is presented that can explain the features of the potential /pH response of both silicon nitride and borosilicate glass ISFETs. The model is easily extended to any two-site system.