A charge-based large-signal model for thin-film SOI MOSFET's

A charge-based large-signal model for thin-film SOI (Si-on-SiO2) MOSFET's, intended for computer simulation of transient characteristics of SOI and 3-D circuits, is developed emphasizing the structural uniqueness of the devices. Closed-form expressions for the quasi-static terminal charges, simpler than those for the bulk MOSFET because of the thin-film structure, are derived in terms of terminal voltages and device parameters, and are used to define the terminal currents. Equivalent circuits, developed from the charge-based model, show that the device can be accurately represented using only real reciprocal capacitances by explicitly accounting for the transient channel transport current ITT. The analytic expression for ITT, obtainable for the thin-film structure, enables the evaluation of the finite-carrier transit delay in the channel and of the corresponding charge nonconservation in the conventional reciprocal-capacitance MOSFET model that does not account for the delay.