Determination of GaN HEMT reliability by monitoring IDSS

In this paper, we investigate the importance and necessity to determine the reliability of GaN HEMT devices by monitoring IDSS during accelerated DC life-test measurements at elevated ambient temperatures. The influence of interrupting this test and cooling the device to measure IDSS at room temperature is investigated. But also methods are investigated to replace this measurement to speed up the reliability measurements and reduce the thermo-mechanical stress induced due to periodically cooling and heating of the devices. One method parameter to monitor is the so called intrinsic IDSS, which is the parameter measured at the ambient temperature of the life-test. The investigation shows that monitoring the intrinsic IDSS is a solid tool to determine the life-time, but too often measurement of this parameter could add additional stress to the device.In addition we saw that intermediate measurements of the output and transfer characteristics did not introduce measureable addition stress as suspected. We also observed that for stress tests at constant PDiss the drift of the gate voltage can be used as failure criterion, although it has no linear relationship to IDSS and therefore the gate voltage drifts more than IDSS and leads to more conservative life-time.