Influence of quasi-ballistic base transport on the small signal y-parameters of Si bipolar transistors

The small-signal forward y-parameters of a Si bipolar transistor are evaluated from a 1-flux solution to the Boltzmann transport equation. For base widths less than 0.1 μm, results begin to deviate significantly from those predicted by the conventional diffusion analysis. In particular, the phase of the y-parameter, an important factor in analog circuit design, is shown to be especially sensitive to quasi-ballistic transport. Compact circuit models will become increasingly inaccurate as base widths continue to shrink. The approach used here eliminates the restriction to a long base and can serve as the basis for improved compact circuit modeling.