Analytical current-voltage relations for compact SiGe HBT models. II. Application to practical HBTs and parameter extraction

For pt. I, see ibid., vol. 46, no. 7, p. 1384-93 (1999). The current-voltage relations derived in the first part of the paper for an idealized SiGe HBT are now checked for transistors with more practical doping profiles: nonabrupt pn junctions, Ge gradient in the base, and heterojunction within the collector region. It is shown that the “idealized” model equations can still be applied if the model parameters are adequately chosen. Sufficient agreement with device simulation results is obtained even in the high-current region. This holds not only for the static behavior but also for small-signal parameters, e.g., y₂₁ and y₂₂, which are more sensitive to potential errors. As another result, all the investigated HBT versions show improved characteristics compared with the idealized HBT. An adequate procedure of how to extract the model parameters from measurement or simulation results is presented. Both the device simulator and the model equations have been successfully checked by measurements. The model has been extended by a transit time model to a complete compact model called SIGEM, which has been implemented in a commercial circuit simulator and successfully used for the design of high-speed IC´s