Investigation of Linearity in the High Electric Field Region for SiGe HBTs Based on Volterra Series

In this paper, avalanche breakdown operation has been demonstrated to have a positive impact on RF linearity performance for silicon germanium (SiGe) heterojunction bipolar transistors (HBTs) due to a nonlinear cancellation mechanism between a breakdown inductance and a base-collector capacitance according to the presented Volterra analysis results. As nonlinearity of breakdown inductance increases, linearity can be improved due to its contribution to nonlinear cancellation when variation of an avalanche multiplication factor (M-1) enlarges. In addition to collector current dependence on M-1, collector-base voltage dependence on M-1 is further taken into account to investigate linearity of SiGe HBTs. Linearity at breakdown can be characterized and presented here in a region no matter whether a multiplication factor increases or decreases. The presented analysis results can be beneficial to the reliability investigation for SiGe HBT linearity in the breakdown region.