A MODEL TO MONITOR THE CURRENT GAIN LONG-TERM INSTABILITY IN ALGAAS GAAS HBTS BASED ON NOISE AND LEAKAGE CURRENT CHARACTERISTICS/

A simple model is proposed to monitor the d.c. current gain long-term instability in the AlGaAs/GaAs heterojunction bipolar transistor (HBT) . It is derived from the theory that the recombination current at the extrinsic base surface increases with time due to the surface degradat ion process. Furthermore, the initial 1/f noise and base leakage curre nt characteristics have been used to provide the needed model paramete rs for the HBT surface recombination mechanism and surface quality, re spectively. The current gain long-term variations calculated from the model for four HBTs compare favorably with those obtained from measure ments. The model proposed is potentially useful to screen unreliable H BT lots without having to carry out the long-term stress test.