Lumped Models for Assessment and Optimization of Bipolar Device RF Noise Performance

We present a method for simulation of RF noise characteristics of both intrinsic and complete Si(Ge) heterojunction bipolar transistors (HBT´s), aiming at support for device design and optimization. RF noise at the intrinsic device level is addressed through an equivalent circuit based on a discretization of partial differential equations describing the transport of minority carriers in quasi-neutral regions. Effects of nonuniform impurity/bandgap distribution and finite velocity recombination at the polysilicon emitter contact are accounted for. Accuracy is verified against analytical results at intrinsic device level. Assessment of noise characteristics of a complete industrial SiGe HBT demonstrates the practical relevance of nonquasi-static effects on noise characteristics. Exploration of the impact of intrinsic base doping profiles on noise performance demonstrates the potential for device optimization.