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Reliability of 100 nm AlGaN/GaN HEMTs for mm-wave applications

: Dammann, Michael; Baeumler, Martina; Polyakov, Vladimir M.; Brueckner, Peter; Konstanzer, Helmer; Quay, Rüdiger; Mikulla, Michael; Graff, Andreas; Simon-Najasek, M.


Microelectronics reliability 76-77 (2017), S.292-297
ISSN: 0026-2714
Fraunhofer IAF ()
Fraunhofer IMWS ()
reliability; GaN HEMT; infrared microscopy; drain-current step stress; TEM; degradation mechanism; Au-diffusion; void; electroluminescence; storage test

The effect of gate metallization and gate shape on the reliability and RF performance of 100 nm AlGaN/GaNHEMTs on SiC substrate for mm-wave applications has been investigated under on-state DC-stress tests. By replacing the gate metallization from NiPtAu to PtAu the median time to failure at Tch= 209 °C can be improved from 10 h to more than 1000 h. Replacing the PtAu T-gate by a spacer gate further reduces the degradation rate under on-state stress, but decreases the current-gain cut-off frequency from 75 GHz to 50 GHz. Physical failure analysis using electroluminescence and TEM cross-section revealed pit and Ni void formation at the gate foot as the main degradation mechanisms of devices with NiPtAu T-gate. High resolution EDX mapping of stressed devices indicates that the formation of pits is caused by a local aluminium oxidation process. Simulation of the stress induced changes of the input characteristics of devices with NiPtAu gate further proves the formation of pits and Ni voids.