Modeling and Simulation of Isfet Microsensor for Different Sensing Films

Electronic circuit simulation programs like SPICE have built-in models for semiconductor devices like MOSFET and BJT. However, they do not provide models for electrochemical sensors like ISFETs (Ion-Sensitive Field-Effect Transistors). This paper presents a behavioral macromodel for ISFET-based pH-sensors implemented using PSPICETM. The macromodel is then utilized to present a comparative analysis of four different insulators, viz.: SiO2, Si3N4, Al2O3 and Ta2O5 used as sensing films for the ISFET. Simulations of ISFET devices with Al2O3 and Ta2O5 sensing films showed better performance with sensitivities of 58.8 mV/pH and 59.15 mV/pH, respectively. This complements the previously reported experimental and theoretical behaviour of ISFETs. Performance of corresponding MOSFET test structure using SILVACO simulations with the same insulators in the gate region is also presented.