Effect of Mixed-Mode Electrical Stress on High-Frequency and RF Power Characteristics of SiGe Hetero-Junction Bipolar Transistors

In this study, we investigate the hot-carrier stress effects on the high-frequency and RF power characteristics of Si/SiGe hetero-junction bipolar transistors (HBTs). By simultaneously applying a high collector current density and a high collector–base voltage on Si/SiGe HBTs, because hot carriers will be induced; they will then degrade device performance. This is interesting because this stress condition is similar to the DC bias condition of a current source RF power amplifier, termed as the "mixed-mode" stress. We find that not only the high-frequency characteristic is adversely affected by but also the output power performance of Si/SiGe HBTs suffers from this electrical stress. In addition, we found that the degradations of the high-frequency and power characteristics of such HBTs are worse in constant-base-current measurement than in constant-collector-current measurement. We finally examined the degradations in terms of parasitic resistance and the ideality factors of base and collector currents using a large-signal model.