The Transition of Threshold Voltage Shift of Al $_{\text{2}}$ O $_{\text{3}}$ /Si $_{\text{3}}$ N $_{\text{4}}$ AlGaN/GaN MIS-HEMTs Under Negative Gate Bias Stress From DC to AC

In this study, the reliability issues are discussed under dc and ac negative gate bias stress (ac-NGBS) in Al $_\text{2}$ O $_\text{3}$ /Si $_\text{3}$ N $_\text{4}$ metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs). Converse degradation between these two stress conditions is discovered. The holes generated by trap-assisted thermionic field emission (TA-TFE) are trapped into the Al $_{\text{2}}$ O $_{\text{3}}$ layer, so that the threshold voltage ( $\textit{V}_{\text{th}}$ ) decreases under dc negative gate bias stress (dc-NGBS). $\textit{V}_{\text{th}}$ increases because of the hot electrons injected into the GaN layer, while the device is turned on quickly under ac-NGBS. In addition, the degradation mechanisms under dc-NGBS and ac-NGBS are confirmed by the OFF-state gate and drain leakages, respectively. Silvaco TCAD is used to validate the degradation mechanism under ac-NGBS. Finally, the characteristics of the $\textit{V}_{\text{th}}$ shift transition from dc to ac NGBS are discussed.