Nonuniform Mechanism for Positive and Negative Bias Stress Instability in β-Ga2O3 MOSFET

In this article, we experimentally study the instability of the key electrical characteristic for the fabricated ${\beta }$ -Ga2O3 MOSFET under positive bias stress (PBS) and negative bias stress (NBS), such as threshold voltage ( ${V}_{{\mathrm {TH}}}$ ), ON-resistance ( ${R}_{{\mathrm {on}}}$ ), subthreshold slope (SS), and hysteresis. An ionized traps model is proposed to explain the instability, which depicts the traps and interfaces states capturing/releasing electrons from the channel. We find nonuniform instability mechanisms. Under the PBS of ${V}_{GS} = 4$ V for 1000 s, the ${V}_{{\mathrm {TH}}}$ and ${R}_{{\mathrm {on}}}$ are increased by 0.8 V and 19%, respectively. The constant interface state density indicates that this instability is caused by border traps in the gate oxide capturing electrons from channel. For the NBS of ${V}_{GS} = -4$ V for 1000 s, the variation in the ${V}_{{\mathrm {TH}}}$ and ${R}_{{\mathrm {on}}}$ is −0.54 V and −8.8%, respectively. The instability is attributed to both the border traps and interface states, and the net increase in activated interface states is $2.25\times10$ 11 cm−2 extracted from hysteresis. Unlike the PBS, the interface states release electrons to bulk traps, and thus the activated interface state density changes. A good agreement with experimental results shows that the proposed model could accurately describe the instability mechanism under both PBS and NBS. These results provide guidance for identifying defects, optimizing device structure, and fabrication process to improve the reliability of $\boldsymbol {\beta } $ -Ga2O3 MOSFET.