Mixed mode double-gate FET model

A general purpose double-gate FET (DGFET) model is presented which is capable of handling a wide variety of DGFET configurations and arbitrary potentials on its four terminals. The heart of the model is the mixed-mode algorithm which, under appropriate bias conditions, transforms the DGFET into two single gate FETs (SGFET) in series. The single gate FET model itself uses a new treatment of the space charge region, allowing the DGFET to be realistically simulated well into the punch-through regime. Sub-threshold and short-channel effects are included and an effective perpendicular electric field, modified by the short-channel charge, is derived for the DGFET and used in mobility calculations. Additional mobility terms can be added to account for scattering at either interface. In addition to currents, voltage dependent capacitances are also derived, including sub-threshold gate to gate capacitances, enabling realistic simulations of coupled circuit noise to be undertaken.