Particle Simulation of Ionic Screening Effects in Electrolyte-insulator-semiconductor Field-effect Transistors

We conduct particle simulations to investigate the screening effect of electrolyte ions in electrolyte-insulator-semiconductor field-effect transistors. The dependency of the ionic screening effect on the distance of a charged target molecule or object from the electrolyte-insulator interface is studied in high frequency as well as low frequency regions. The electric transfer coefficient defined as the ratio of the channel charge to the target one is simulated. It is found that the frequency region where its magnitude and phase change appreciably, coincides with the corner frequency of the Lorentzian noise spectrum originating from electrolyte ionic thermal motions. A simple capacitance model is presented to understand the frequency dependence of the ionic screening effect. It is found that the ionic screening effect can be overcome by the high-frequency oscillation of target molecules.