This article presents a comprehensive study on the occurrence mechanism, instability analysis, and suppression methods of self-sustained turn-off oscillation, which occurs on cascode gallium nitride high electron mobility transistors (cascode GaN HEMTs). In the beginning, the oscillation waveforms are analyzed, which indicate that the occurrence of the oscillation is determined by test circuit instability. Based on the double pulse test, the impact of the load current $I_L$, dc bus voltage $V_{\text{DC}}$ and gate resistance $R_{G}$ on the self-sustained oscillation is identified. To investigate the instability of the resonant circuit, a small-signal ac model of the resonant circuit is derived. Based on the model, the influences of various parameters on the self-sustained oscillation are analyzed. The analyses reveal the possible methods which can suppress the oscillation. The effectiveness of the proposed methods is validated by the experimental data and simulation results in the end.

In this paper, an analytical model is proposed to model collector-emitter voltage rising slope ( dV_CE/dt ) of field-stop (FS) IGBT during turn-off transient. Thanks to TCAD simulation, the internal physics of the FS IGBT during V_CE rise transient is investigated. Based on the improved understanding of the V_CE rise transient, an analytical solution of the excess carrier distribution in the N-base region and FS layer is derived. An analytical model for dV_CE/dt of FS IGBT is also proposed. The temperature dependency of various silicon material and device parameters are included in the model. In the end, the double-pulse tests are performed on 650V/40A and 1200V/40A FS IGBTs. The test results are compared with the analytical predictions and good agreement is obtained.

This article presents an experimental investigation on the short-circuit (SC) instability of several commercially available cascode gallium nitride (GaN) high-electron-mobility transistors (HEMTs). In the SC test, self-sustained oscillation is observed during the SC transient. The SC oscillation features some unique characteristics. The gate resistor shows very weak damping effect on the SC oscillation. The SC oscillation thereby cannot be suppressed by utilizing a large gate resistor. With the increase in the dc-bus voltage, the SC oscillation greatly amplifies and becomes more unstable. When the dc-bus voltage reaches 200-250 V, catastrophic failure occurs. In the SC test, two distinct failure modes, which are related to the failure of low-voltage (LV) MOSFET and depletion-mode HEMTs (DHEMTs), are identified. Based on the experimental evidence and simulation study, the root causes of the failure are clarified in the end.

This article presents a study on the short-circuit (SC) instability of p-doped gate gallium nitride (p-GaN) high-electron-mobility transistors (HEMTs). Under SC condition, self-sustained oscillation occurs when a package stray inductance is introduced in a common source. The SC oscillation features some unique characteristics. With higher dc-bus voltage, the SC oscillation tends to be more unstable. The SC oscillation of p-GaN HEMTs is, thereby, a real threat to the converter operation. When the common-source inductance is eliminated or a larger gate resistor is utilized, the SC oscillation can be dampened. Due to the SPICE simulation, the self-sustained SC oscillation is reproduced. The analyses on the simulated waveforms reveal a positive feedback mechanism that excites the SC oscillation. An analytical model is, thereby, derived to analyze the instability of the positive feedback system. The analyses reveal that the SC oscillation becomes more unstable ,,when the power loop or gate loop has smaller stray inductances, which makes some conventional oscillation suppression methods invalid. To avoid SC oscillation, some effective guidelines are proposed at the end of the article.

Under certain conditions, self-sustained oscillation may occur during reverse recovery transient of high-side silicon carbide (SiC) MOSFET body diode in the half-bridge circuit. In this article, two distinct positive feedback mechanisms that can excite the self-sustained oscillation are identified based on the double-pulse test. To investigate the instability of the two types of oscillation, a small signal ac model of the half-bridge circuit is proposed. With the model utilized, the parametric sensitivities of various parameters on the self-sustained oscillation are analyzed. The analyses reveal the oscillatory criteria, which provides effective guidelines to prevent the oscillation. In the end, the oscillation prevention guidelines are validated by the experiment. The experimental results demonstrate that the proposed theoretical treatment can provide reasonable guidelines to suppress the two types of self-sustained oscillation.