Analysis of Abnormal C–V Hump on Si₃N₄ MIS-HEMT With Mesa Isolation Under Negative Gate Bias Stress

In this study, negative gate bias stress (NGBS) is applied to the Si3N4 metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs). The gate electron injected into the Si3N4 dielectric layer and the holes generated by the impact ionization trapped into the AlGaN layer are the two main degradation mechanisms, which cause the unstable threshold voltage. Moreover, it is discovered that an abnormal <tex-math notation="LaTeX">C </tex-math> – <tex-math notation="LaTeX">V </tex-math> hump is generated after NGBS because of the uneven hole trapping at the AlGaN near the channel under the gate. The unusual direction of the electric field, which is related to the mesa isolation technology, is observed under NGBS condition in the Silvaco TCAD simulation. The location of the hole trapping is verified by the positive gate bias after NGBS during the recovery time. Finally, the device without the mesa isolation is used to verify the abnormal degradation results.