GaN-ON-Si Failure Mechanisms and Reliability Improvements

The degradation of 36mm AlGaN/GaN HFETs-on-Si under DC stress conditions has been studied on a large number of nominally identical devices that were chosen randomly across a production process. A common and primary degradation phenomenon was observed in the devices. A combination of electrical and physical analysis was used to identify a possible failure mechanism related to the Ni/Au Schottky gate diode that appears to explain the degradation of the FET. Based on the analysis, a gate anneal step was added into the fabrication process of AlGaN/GaN HFETs-on-Si. Nominal devices processed using a gate anneal showed (a) a modified gate metal-semiconductor interface (b) forward diode characteristics that are unchanged upon stress and (c) improvement in overall reliability relative to control devices