Abstract

GaAs/GaAlAs HEMT's are rapidly replacing conventional FET's for applications where high gain and low noise figure at high frequencies are needed; for this reason we began a qualification program on them, with the goal of evaluating the possible criticalities that could affect long term performances. The program includes electrical characterization, thermal storages and operating life-tests on commercially available devices, coming from four different manufacturers. During the electrical characterization we especially focused on "kink" effect, concluding that it should be ascribed to trapping/detrapping mechanisms in the AlGaAs layer; even if this phenomenon is peculiar of HEMT's, we found no evidence of any possible detrimental effect on reliability. Thermal storage at 250 °C caused Schottky barrier degradation in the devices with Ni or Ti used as interdiffusion barrier between Al and GaAs; these degradations affect devices performances but cannon be considered peculiar of HEMT's technology, as they were found in low noise FET's too. During biased life-test at Tch = 175 °C, no significant parametric degradation was found up to 2500 test hours.