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

Self-aligned AlGaAs/GaAs single heterojunction bipolar transistors (HBT;s) were fabricated using an advanced processing technology for microwave and m illimeter-wave power applications, These devices were processed simultaneou sly, on different epilayers with similar Layer structure design supplied fr om different vendors. They showed similar de characteristics (current gain, beta = 30) and their microwave performance was also identical (f(T) = 60 G Hz, f(max) = 100 GHz). The HBT's showed different noise and reliability cha racteristics depending on their epilayer origin, HBT's from the high-reliab ility wafer showed MTTF of 10(9) h at junction temperature of 120 degrees C . They also presented very small 1/f noise with corner frequencies in the r ange of a few hundred Hz, Devices were subjected to bias and temperature st ress for testing their noise and reliability characteristics. Stressed and unstressed devices showed generation-recombination noise with activation en ergies between 120-210 meV, Stress was found to increase the generation-rec ombination noise intensity but not its activation energy, These HBT's did n ot show any surface-related noise indicating that processing did not signif icantly influence noise characteristics. It was found that the base noise s pectral density at low frequency can be correlated to the device long term reliability.