Numerical and Analytical Results for the Polysilicon Gate Depletion Effect on MOS Gate Capacitance

Analytical and numerical gate capacitance models with polysilicon (poly) depletion effect are studied by directly solving the coupled Poisson equations on the poly and silicon sides. The poly depletion effect is known to significantly reduce surface potential, channel current and gate capacitance values. Different oxide thicknesses and doping levels of the MOS device are studied, and the final analytical gate capacitance model exhibits an excellent fit with numerical data. The analytical model is determined using asymptotic methods. The models presented here give accurate results for the poly depletion effect and this new information may be used to improve SPICE circuit simulations in advanced VLSI since the gate depletion effect is significant in current nanoscale MOSFET devices.