Compact modeling of high-frequency, small-dimension bipolar transistors

Recent progress in the development of compact models for high-speed bipolar transistors with quasi-ballistic base widths (on the order of a mean-free path length) is summarized. The correctness of basing such models on the drift-diffusion equation is examined by comparing results with solutions to the Boltzmann transport equation. Useful and well-founded compact expressions are presented for important dc and ac device parameters.