Self-Heating Effect in Silicon-Germanium Heterostructure Bipolar Transistors in Stress and Operating Conditions

In recent times many systems in a wide range of application fields (e.g., health, material science, security, and communications) exploit the mm-and sub-mm-wave spectrum, which dramatically sped up the growth of the BiCMOS technology integrating silicon germanium (SiGe) heterojunction bipolar transistors (HBTs) and passives. Today, the reliability of such devices is of primary concern, and particular attention is given to the device self-heating (SH), the importance of which is supposed to increase with the device scaling. In this work we develop a TCAD model for SiGe HBT devices that is used to investigate the SH effects in SiGe HBTs both in operating and stress conditions. We underline the different role played by impact ionization and carriers' and lattice heating on the device degradation. Results show the important role played by the back end-of-line (BEOL) and by the substrate thermal resistance in dissipating the heat generated by impact ionization and hot carriers. Simulations of the SH effects in stress conditions excluded annealing as the possible reason for the degradation dynamics reported in the literature, while simulations of stressed devices in measurement conditions revealed the presence of a hole hot spot that suggests a possible physical mechanism involved in the degradation slowdown at long stress times reported in the literature.