Reliability and degradation mechanism of 0.25 µm AlGaN/GaN HEMTs under RF stress conditions

The reliability and degradation mechanism of AlGaN/GaN single stage amplifiers after 10 GHz stress at a drain voltage of 42 V and channel temperatures above 250°C was investigated using electroluminescence (EL) imaging, infrared thermography, and TEM. The extrapolated median lifetime extracted from the Arrhenius plot is 510⁵ h at a channel temperature of 200°C, and the activation energy is 1.7 eV. Intermediate measurements during stress show a strong decrease of maximum drain current and gate leakage current. Physical failure analysis of faster degrading devices using EL showed that the 8 gate finger device changes from a homogeneous distribution before stress, where all gate fingers show approximately the same EL intensity, to a highly inhomogeneous distribution after stress, where one central gate finger shows a much higher EL intensity as compared to the others. Infrared thermography shows that the finger with the highest EL intensity operates at a higher channel temperature. TEM images of one stressed device reveal a dislocation below the gate on the source side edge and the formation of a void below the gate foot as the possible root cause of the observed degradation.