Capacitance Model for Four-Terminal DG MOSFETs

摘要

We present an intrinsic capacitance model for undoped-channel full-deplete DG MOSFETs with two independent gates of different gate-oxide thickness. The basis of the model is double charge-sheet four-terminal compact model of DG MOSFET with carrier velocity saturation. We considered five intrinsic capacitances C_(G1S), C_(G1D), C_(G2S), C_(G2D), and C_(G1G2). Since total charge in the channel can be calculated analytically, these capacitances are obtained by differentiating it. Anomaly of C_(G1G2) was found in the sub-threshold region when the transistor is in the double charge-sheet mode. This can be explained by the redistribution of the carriers between two charge-sheets when the gate voltages is changed, resulting in the screening current against the perpendicular electric field. To remedy this effect, it was found that the charge-sheets should be placed at the mean position of the carriers, instead at the silicon-insulator interface.