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Schottky-type p-GaN gate Gallium Nitride High Electron Mobility Transistors (GaN-HEMTs) suffer from threshold voltage ( Vth ) instability phenomenon. Both positive and negative Vth shifts are reported when device undertakes the voltage bias, but the impact of this Vth instability phenomenon on device switching behaviors is less investigated. In this study, the drain-source voltage ( Vds ) induced bidirectional Vth shift in hard-switching condition is characterized and decoupled by an H-bridge based double-pulse test (DPT). Subsequently, the influence of Vth shift on switching behaviors is theoretically analyzed and demonstrated through SPICE simulation and experiment, showing how a positive shifted Vth can reduce the device turn-on commutation speed and increase the switching losses, and vice versa. The results suggest that the Vth instability phenomenon should be considered in accurate switching modeling.

Gallium nitride high-electron-mobility transistors (GaN-HEMTs) enable fast switching commutation due to their small parasitic capacitances, which necessitates the effective gate driving techniques. Gate drivers with split-output topology offer advantages such as reducing the risk of false turn-ON and minimizing the size of gate loop. However, the output capacitance of gate driver in this configuration may reduce the commutation speed of GaN-HEMTs, and values of this capacitance are overlooked in the gate driver datasheets. This paper highlights the critical role of gate driver output capacitance on the switching performance of GaN-HEMTs, which has been discussed by proposing an analytical model and demonstrated through both simulations and experiments. The results show that this capacitance can slow down the switching speed specifically in the split-output gate driver configurations, leading to inaccurate switching waveform predictions. Furthermore, a measurement method and corresponding output capacitance data for a series of commercially available gate drivers are presented. These findings offer practical guidance for gate driver selection in GaN-HEMT applications.

This work investigates the power GaN-HEMTs switching behaviour differences resulted from usage of two gate driving configurations: single and split outputs. The analysis based on simulation and experimental results show that GaN-HEMTs could switch slower and cause higher switching losses when the split output configuration is used. This is because the output capacitance (Coss) of MOSFETs inside gate driver will be charged during the turn-on process of GaN-HEMTs, and this charging process can reduce the charging speed of input capacitance (Ciss) of GaN-HEMTs. Moreover, the gate resistance and parasitic inductance are the main parameters selected for analysis, and their distribution can amplify this effect by increasing the impedance ratio of turn-on and turn-off loop. This research provides guiding suggestions for gate driver and high-efficiency GaN-HEMTs power module design.

A new method is proposed in this paper to investigate the influence of current collapse effect on the Id−Vds characteristics of GaN-HEMTs in high voltage region based on a modified H-bridge circuit. The measured Id−Vds characteristics with and without the Vds bias are compared, which shows the effect of charge trapping due to the Vds bias on device Id−Vds characteristics in saturation region. These data will be used for a device model including the current collapse effect in full Id−Vds region.

Cette thèse s’intéresse à l’influence de la variation de la tension de seuil (Vth) et de la capacité de sortie du driver de grille sur le comportement en commutation des transistors à haute mobilité d’électrons en nitrure de gallium (GaN-HEMTs). Comprendre ces facteurs est crucial pour une modélisation précise des dispositifs et pour une bonne estimation des performances en commutation avant d’employer les GaN-HEMTs dans les convertisseurs de puissance. La première partie de la thèse présente l’origine et les méthodes de caractérisation du phénomène de variation de Vth dans les GaN-HEMTs. Dans le deuxième chapitre, une méthode de mesure in- situ de Vth est proposée pour caractériser le phénomène de variation de Vth dans des conditions de commutation douce, en modes mono-impulsion et multi-impulsion. Le troisième chapitre étudie l’impact de la variation de Vth sur le comportement en commutation à travers une analyse théorique, démontrée par simulation et par validation expérimentale. Dans la dernière partie, l’influence de la capacité de sortie du driver de grille sur le comportement en commutation des GaN-HEMTs est examinée dans deux configurations de grille courantes : sortie unique et sortie séparée. Des circuits équivalents pour les deux configurations sont présentés pour illustrer leur effet sur les performances de commande rapprochée des transistors. Les résultats montrent qu’aussi bien l’augmentation de Vth que la capacité de sortie du driver de grille à sorties séparées peuvent ralentir la vitesse de commutation à la mise en conduction des GaN-HEMTs.