Non-quasi-static modeling/implementation of BJT current crowding for seminumerical mixed-mode device/circuit simulation

An non-quasi-static (NQS) model for transient current crowding in advanced bipolar junction transistors (BJTs) 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. The novel modeling/implementation is based on the use of the previous time-step analysis, which is 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 μm