A charge sheet capacitance model of short channel MOSFETs for SPICE

An analytic charge sheet capacitance model for short-channel MOSFETs is derived and implemented in SPICE. It is based on a surface potential formulation which computes the approximate surface potential without iterations. The DC current, charges, and their first and second derivatives are continuous under all operating regions. Equations for node charges are derived to guarantee charge conservation. Short-channel effects such as velocity saturation, channel-length modulation, and channel-side-fringing-field capacitances are included in the model equations. The model shows good agreement with the measured gate capacitance for long- and short-channel MOSFETs. The SPICE simulation of a ring oscillator using this model shows the significant variation of circuit performance due to the short-channel effects on capacitances.<
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