Degradation of 0.25μm GaN HEMTs under high temperature stress test

The temperature dependence of device degradation of AlGaN/GaN HEMTs on SiC substrate with a gate length of 0.25μm has been investigated. The critical surface temperature, where device degradation sets in has been determined using drain-current step-stress tests in combination with infrared microscopy. Using this fast reliability test, devices with different passivation technologies have been compared and, by optimizing the passivation technology, the critical temperature at which degradation of the threshold voltage begins has been improved from 310°C to above 330°C. Storage tests at 300°C in nitrogen atmosphere confirm the improvement in high temperature stability. Physical failure analysis using electroluminescence and TEM/EDX cross-section revealed void formation and Au-diffusion at the gate as the main degradation mechanisms of devices with the conventional passivation technology.