A compact physical large-signal model for high-speed bipolar transistors at high current densities—Part II: Two-dimensional model and experimental results

In this second part of the paper, the one-dimensional transistor model presented in Part I [1] is extended to the two-dimensional case, i.e., to real transistors. For this, well-known effects like emitter current crowding, emitter sidewall injection, and collector current spreading in the epitaxial collector were roughly taken into account, as well as the modulation of the internal base resistance. Furthermore, methods for determining the model parameters are given. For checking the model, high-speed transistors (fT≈ 7 GHz) with small emitter stripes ( ≈2 µm) were fabricated. Experimental results agree well with the simulated ones for both the dc characteristics and the (more important) switching behavior even far within the high-current region. Switching times, measured for single transistors, were in the range of 100 to 200 ps, typical of modern high-speed integrated circuits. The complete model, which is called HICUM (from "high-current model"), was already implemented in the circuit analysis program SPICE 2.