NON-QUASI-STATIC MODELING IMPLEMENTATION OF BJT CURRENT CROWDING FOR SEMINUMERICAL MIXED-MODE DEVICE CIRCUIT SIMULATION

A non-quasi-static (NQS) model for transient current crowding in advanced BJT's is presented. The model, which characterizes a time-dependent effective bias on the emitter-base junction in a seminumerical analysis, is intended for circuit simulation and has been implemented in MMSPICE [1]. The novel modeling/implementation is based on the use of the previous time-step solution in the current time-step analysis, which in fact could allow general accounting for NQS effects in seminumerical mixed-mode device/circuit simulation. Demonstrative simulations, supported by purely numerical ones, show that for the BJT switch-on transient, the NQS current crowding causes an added delay and tends to become insignificant only when the emitter width (W(E)) is scaled to deep-submicron values, and that for the switch-off transient, the added delay is negligible, at least for W(E) < 2 mu-m.