An Analytical Model for the Non-Quasi-Static Small-Signal Behaviour of Submicron MOSFETs

A new, analytical Non-Quasi-Static model, in terms of admittance parameters, for the small-signal behaviour of short channel MOSFETs is presented. The relevant short channel eeects are included explicitly in the derivation of the model. The eeects of approximating the exact analytical solutions are discussed. A new approximation for extremely high frequencies is proposed. The model is consistent with previously published low frequency models and shows good agreement with 2D device simulations and measurements. Finally the innuence of parasitics is illustrated. Symbol Meaning Unit gain factor AV ?2 body eeect coeecient V 1=2 coeecient related to the body eeect A transversal eld mobility reduction parameter V ?1 C lateral eld mobility reduction parameter V ?1 mobility m 2 V ?1 s ?1 0 low-eld mobility m 2 V ?1 s ?1 fall-time s F Fermi level in the substrate V ! angular frequency s ?1 C ox oxide capacitance per unit area Fm ?2 C ij terminal j to terminal i capacitance F E C critical eld for velocity saturation eeect V m ?1 E x lateral component of electrical eld V m ?1 I i current through terminal i A i(x) small signal part of J(x) Am ? 1 i i small signal part of I i A J 0 DC part of J(x) Am ? 1 J(x) current density in channel Am ?1 L channel length m L ee eeective channel length m L sub underdiiusion length m Q B bulk charge C q B bulk charge density Cm ?1 t time s t T transit time s U(x) eeective gate channel potential V u i small signal part of V i V u(x) small signal part of U(x) V u GT small signal part of U GT V V i potential of terminal i V V ij voltage between terminal i and terminal j V V GT gate drive, V GS ? V T V V T threshold voltage V V (x) channel potential V v GT DC part of U GT V v(x) DC part of U(x) V W channel width m x lateral position in channel m Y ij terminal j to terminal i admittance parameter S A,B,D,E auxiliary variables in NQS model