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In this study, the reliability issues are discussed under dc and ac negative gate bias stress (ac-NGBS) in Al2O3/Si3N4 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 Al2O3 layer, so that the threshold voltage ( ${V}_{\text {th}}$ ) decreases under dc negative gate bias stress (dc-NGBS). ${V}_{\text {th}}$ 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 ${V}_{\text {th}}$ shift transition from dc to ac NGBS are discussed.

In this study, X-ray irradiation of metal–insulator–semiconductor (MIS) AlGaN/GaN high-electron-mobility transistors (HEMTs) is performed. After the X-ray irradiation, the threshold voltage ( ${V}_{\text {th}}{)}$ shift and ON-state current ( ${I}_{\text {on}}{)}$ variation are observed. However, after a recovery period, the degradation trend of ${V}_{\text {th}}$ and that of ${I}_{\text {on}}$ are in opposite directions. Such opposite degradations are demonstrated and explained in this study. As X-rays irradiate the devices, holes, and defects are generated in the GaN layer and Si3N4 layer, respectively. To prove the degradation mechanism induced by X-rays in MIS HEMT, the following characteristics are offered. The drain current ( ${I}_{d}{)}$ and the source current ( ${I}_{s}{)}$ under the X-ray irradiation are introduced to prove the hole generation. The two-step degradation of the gate current ( ${I}_{g}{)}$ after X-ray irradiation provides evidence of the formation of defect states. Moreover, the different degradation behaviors between Schottky-gate HEMT and MIS HEMT are compared and verification of the position of generation of defect states in the Si3N4 layer is given accordingly.

This work proposes forming-free HfO2-based resistance random access memory (RRAM) using X-ray irradiation which overcomes the bottleneck of the conventional forming process, that of the need for a larger forming voltage with scaling. In addition, a large irradiation area is beneficial to the mass production of memory devices. This forming-free device has a better memory window compared to the device without X-ray irradiation. Moreover, the forming-free device has good reliability as the device without X-ray irradiation. To analyze the physical mechanism, the conduction mechanism was investigated by the current-fitting technique, and irradiation experiments with varying X-ray energies and times were performed. Finally, a physical model is proposed to explain the mechanism of the forming-free RRAM from X-ray irradiation.