Lateral AC current flow model for metal-insulator-semiconductor capacitors

The admittance-voltage characteristic of a metal-insulator-semiconductor capacitor is explained in the depletion-inversion range for the case in which the entire surface of the semiconductor is inverted by charges in the insulator and the frequency is too high for minority carriers to follow. Lateral ac current flow into the inverted layer beyond the field plate has to be considered. The model is verified by several experiments and a simple equivalent circuit is shown to quantitatively fit the characteristics. The lateral current model is used to explain drift in the characteristics caused by ion migration along the oxide surface under dc bias. This type of ion migration is separated from true changes of charge density within the insulator.