Advanced Modeling of Silicon-Germanium Heterojunction Bipolar Transistors

Silicon-Germanium Heterojunction Bipolar Transistors (SiGe HBTs) are perfectly suited for high-speed electronics. Since the fabrication costs per design cycle are rapidly increasing with progressing frequency and complexity of the systems, accurate compact models are essential in order to enable robust circuit design. This thesis focuses on selected important physical effects in advanced SiGe HBTs, which have been either insufficiently modeled or completely missing in conventional compact models. New compact model equations for the transfer current were derived and successfully applied to a large set of different technologies. Hereby, the "Generalized Integral Charge Control Relation" was used as a foundation. A physics-based model utilizing small-signal parameters obtained from measurements is derived for modeling the current dependent collector charge. A brief chapter about substrate effects in bipolar transistors comprises the derivation of a compact model for the bias-dependent substrate resistance as well as a proper partitioning of the substrate capacitance.
New extraction methods for compact model parameters are introduced and the application of existing methods to advanced processes is discussed. The derived joint extraction method for the emitter and thermal resistance as well as a scalable model for the transfer current have been successfully applied to experimental data of fast HBTs. The derived model equations were applied to a selected very advanced SiGe HBT process developed by IHP. Highly accurate models for DC- and small-signal as well as for large-signal characteristics are presented.