PH, pK and pNa detection properties of SiO2/Si3N4 ISFET chemical sensors

Abstract

This article reports the technological fabrication and the electrical characterisation of SiO2/Si3N4 ion sensitive field effect transistors (ISFET) for the detection of H+, K+ and Na+ ions. ISFET chemical sensors show quasi-nernstian pH response with sensitivities around 54 mV/pH. pK and pNa measurements are also investigated, evidencing sensitivities lower than 20 mV/pH and non-nernstian pH-dependent phenomena for the highest K+ or Na+ concentrations (pK and pNa, respectively, lower than 4 and 3). It is shown that the detection properties of H+, K+ and Na+ ions are dependent on each other, being responsible for saturation effects for the highest concentrations. It is finally concluded that SiO2/Si3N4 ISFETs are well adapted for the pH measurement, can be used for the pK or pNa measurements in the case of buffered solutions but are not fully suitable for multi-ion detection in the case of medical analysis.