Fast-Pulsed Characterization of RF GaN HEMTs in Lifetest Systems

We report a new application of microsecond-pulsed current-voltage characterization of field-effect transistor (FET) devices; namely, in compact, mutlichannel DC and RF lifetest systems. This application is important for routine monitoring of trap-related signature parameters in lifetests, and is particularly useful for study of GaN high electron mobility transistors (HEMTs) due to the wide variety of traps in the present generations of this technology. Also, we report a systematic approach to identifying the significant populations of traps, their general locations, and the qualitative changes that occur during lifetesting. This enables quick evaluation of device quality, likely degradation mechanisms and their signature parameters, and degradation rates-all with good statistics (up to 30 specimens simultaneously in one of our systems) and high reproducibility (± a few %). We use static I-V measurements as well, to separate the slow trap effects (longer than 10 min) from the fast ones (a few microseconds to about 1 min). We illustrate these techniques, with measurements of unstressed specimens of two GaN HEMT technologies. Evolution of the traps as the lifetests proceed will be described in a later paper.