Capacitance-voltage characteristics of floating gate electrolyte-insulator-semiconductor capacitors

This paper focuses on the floating gate structure that is the basis of the floating gate ISFET. The study is based on the Floating Gate Electrolyte Insulator Semiconductor (FGEIS) capacitor, which is the parallel structure to the Metal Oxide Semiconductor (MOS) capacitor found in MOSFETs. The floating gate consists on an aluminum layer on silicon dioxide covered by a sensing layer of aluminum oxide or silicon nitride. Both layers are widely used to obtain pH sensitivity. The devices are studied through Capacitance-Voltage characteristics, using a buffer electrolyte with pH=7. In this study a Teflon jig provides good mechanical contact and interface to the solution. The measurements are performed at 1 KHz. High frequency characteristics are observed. Depending on the fabrication process different hysteresis is observed in the counter-clockwise direction.