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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.

High-electron-mobility transistor (HEMT) based on Gallium Nitride (GaN) material is often designed for high-voltage operating conditions because of the high electric critical field of GaN material. However, such devices are often prone to the hot carrier stress (HCS) effect under high drain voltage and on-state conditions. Therefore, the HCS effect is an important consideration for reliable GaN HEMT devices. The Al2O3/Si3N4 bilayer gate dielectric AlGaN/GaN metal–insulator–semiconductor (MIS) HEMT has many advantages such as low gate leakage current and interface defects. However, the degradation phenomena observed in this device under HCS is very different from those of Si3N4 MIS HEMTs discussed in several reported studies. In this work, the HCS degradation results of Si3N4 MIS HEMTs and Al2O3/Si3N4 bilayer MIS HEMTs are both investigated and compared. The HCS degradations in Al2O3/Si3N4 bilayer MIS HEMTs are also examined and illustrated in depth. Finally, different stress voltage conditions of HCS are applied and the C-V measurements are carried out in order to confirm the degradation behaviors of MIS HEMT device.

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.