Graphene Field-Effect Transistor for pH Sensing application: Compact Modelling and Simulation Study

Graphene field effect transistors (FETs) are good candidates for sensing applications thanks to their high charge carrier mobility, high flexibility, and biocompatibility and the ideal coupling between graphene charge carriers and surface potential. This work presents the development of an accurate physic based model for Graphene based Ion-Sensitive Field Effect Transistor (Gr-ISFET) using site binding theory and Guoy-Chapman-Stern capacitance model. This model can help designer's community to explain the sensitivity mechanism of such devices and hence predict the optimal structure in order to get the best sensing performances. For model precision assessment, simulated electrical ambipolar characteristics for the device drain to source conductance Gds are verified with experimental measurements for ionic and non-ionic solution. Good agreement was observed. The major finding of this work was that simulation results had showed that Gr-ISFET containing oxide film fabricated by stacking high-k materials as SiO2, Al2O3 and HfO2 leads to high pH sensor sensitivity. This is essentially due to the rich oxide's surface with hydroxyl groups which enhances surface binding and increases sensitivity.