Long-term base current instability: a major concern for AlGaAs/GaAs HBT reliability

This paper provides an overview of the long-term base current instability in the AlGaAs/GaAs heterojunction bipolar transistor (HBT), which is a main mechanism governing the HBT long-term current gain drift and thus a major concern for the HBT reliability. Topics covered include: (1) types of base current instability and their underlying physical mechanisms; (2) leakage currents in the HBT and their relevance to the reliability; (3) electro-thermal interaction and their impact on the HBT reliability; and (4) analytic model for predicting the HBT mean time to failure (MTTF). Measurements and device simulation results are also included in support of the modeling and analysis.