Optimisation of an electronic amplifier applied to electrolyte/insulator/semiconductor structure

This paper reports on the final development of a MOSFET-based amplifier for the electrical characterisation of chemical field-effect capacitors (ChemFEC) based on electrolyte/insulator/semiconductor (EIS) capacitive structure. Experimental demonstration is performed through the study of SiO₂/Si₃N₄ ion sensitive field-effect capacitor (ISFEC) sensors for pH measurement. This study deals with the amplification's properties according to the ISFEC and MOSFET electrical characteristics. Thus, the ISFEC transition from the accumulation to the inversion regime is shown to be responsible for a non-linear phenomenon. Nevertheless, thanks to a compromise between the ISFEC flat-band voltage and the MOSFET threshold voltage, linear responses are evidenced on the [2-12] pH range. Thus, the non-linear phenomenon observed in previous works is clarified. The detection structure evidences linear responses, which is an essential parameter for sensors. Finally, high detection sensitivities are obtained on a small pH range due to this non-linearity.