An Improved Transfer Current Model for RF and mm-Wave SiGe(C) Heterojunction Bipolar Transistors

The carrier transport in advanced SiGe heterojunction bipolar transistor (HBT) process technologies exhibits bandgap-related transport effects that not only impact the transconductance and output conductance characteristics, but are also difficult to describe accurately by compact models. This paper addresses the modeling of bandgap-related effects in the collector current by formulating an improved version of a generalized integral charge-control relation (GICCR). As a result, the experimentally observed degradation of the transconductance at low and medium current injection, which is a strong function of the Ge grading, as well as the output conductance are described by simple bias- and temperature-dependent formulations of the GICCR weight factors. The derived formulations fit seamlessly into the compact model HICUM/L2. The extended model shows excellent agreement over a wide bias and temperature range with the experimental data of a large variety of SiGe HBTs from technologies of different manufacturers, including production and most advanced lab processes.