Relation between low-frequency noise and long-term reliability of single AlGaAs/GaAs power HBTs

Self-aligned AlGaAs/GaAs single heterojunction bipolar transistors (HBTs) were fabricated using an advanced processing technology for microwave and millimeter-wave power applications. These devices were processed simultaneously, on different epilayers with similar layer structure design supplied from different vendors. They showed similar dc characteristics (current gain, /spl beta/=30) and their microwave performance was also identical (f/sub T/=60 GHz, f/sub max/=100 GHz). The HBTs showed different noise and reliability characteristics depending on their epilayer origin. HBT's from the high-reliability wafer showed MTTF of 10/sup 9/ h at junction temperature of 120/spl deg/C. They also presented very small 1/f noise with corner frequencies in the range of a few hundred Hz. Devices were subjected to bias and temperature stress for testing their noise and reliability characteristics. Stressed and unstressed devices showed generation-recombination noise with activation energies between 120-210 meV. Stress was found to increase the generation-recombination noise intensity but not its activation energy. These HBTs did not show any surface-related noise indicating that processing did not significantly influence noise characteristics. It was found that the base noise spectral density at low frequency can be correlated to the device long term reliability.