Reliability Assessment in Different HTO Test Conditions of AlGaN/GaN HEMTs

This study reports on a reliability investigation of AlGaN/GaN HEMTs submitted to life tests in High Temperature Operating (HTO) conditions at 150 degrees C, 175 degrees C, 275 degrees C and 320 degrees C. These life tests showed two different degradation steps of the drain current. One is occurring in the first tens of hour of the life test and characterized by a decrease of the drain current. The evolution of the electrical characteristics during ageing does not depend on the bias conditions but rather on the channel temperature. This degradation mode is characterized by a high activation energy of 1.2eV. The small changes of electrical characteristics observed during the life tests results from a combination of trap-related effects before stabilization sets in. The second failure mechanism observed during the HTO tests at 275 degrees C and 320 degrees C results in a higher drain current decrease. Moreover, no stabilization of the parameter drifts was observed before the end of the tests. Pulsed I-V measurements show a large evolution of gate lag and drain lag rates after HTOT275 and HTOT320 life tests. LF 1/f noise after the life tests at high temperature drastically increased by more than two orders of magnitude while it hardly changed after 2000 hours of life test at 150 degrees C and 175 degrees C. It results that the temperature is considered as an acceleration factor of the degradation affecting the conduction channel. TEM observations revealed similar damages in the gate finger cross-section of aged devices after the HTOT275 and HTOT320 life tests. These results could point out a degradation mechanism associated with the inverse piezoelectric effect.