Mohamed Belguith

GaN power devices used in high-power-density converters face significant thermal-management challenges because substantial heat is generated within a compact active region and transferred through the device–Printed Circuit Board (PCB) interface. This study investigates the influence of PCB dielectric-material selection on the coupled thermal and electrical behavior of a 48 V/12 V GaN half-bridge converter. Flame Retardant 4 (FR4), Hydrocarbon ceramic laminate material RO4000 series (4003) (RO4003), and polybenzoxazole (PBO) were compared using a reduced steady-state thermal-resistance network, three-dimensional finite-element simulations in Ansys Icepak, parasitic-capacitance extraction in Ansys Q3D, and switching simulations in LTspice. Both analytical and numerical models produced the same thermal-performance ranking, with PBO providing the lowest junction temperature. Under identical geometry, power dissipation, and boundary conditions, the Finite Elements Method (FEM) results showed a reduction in the maximum junction temperature from 225 °C for FR4 to 159 °C for PBO. The extracted layout-associated capacitances were also reduced by approximately 30–38% with PBO relative to FR4. This decrease produced a slight reduction in the switching-node falling time and lowered the calculated transistor loss from 3.118 W to 3.102 W. The results show that PCB dielectric selection is primarily a thermal-design parameter, while its electrical influence remains modest under the investigated operating conditions.

Les convertisseurs statiques à base de transistors GaN offrent des performances élevées en termes de densité de puissance et de rendement, favorisant leur adoption dans les systèmes embarqués automobiles. Néanmoins, leur fiabilité à long terme dans des conditions sévères reste à évaluer. Cette thèse étudie l’effet du vieillissement accéléré par cycles de court-circuit sur la compatibilité électromagnétique (CEM) de convertisseurs DC/DC GaN destinés aux véhicules électriques.Un convertisseur Buck optimisé a d’abord été conçu et modélisé à l’aide d’approches électrothermiques et CEM avancées, puis validé expérimentalement. Les résultats ont permis d’identifier des phénomènes thermiques critiques et de proposer des stratégies de gestion thermique améliorant la fiabilité du dispositif.Le convertisseur a ensuite été soumis à des tests de vieillissement accéléré, révélant une corrélation entre la dégradation des paramètres internes des transistors GaN et l’évolution des émissions EMI conduites et rayonnées. Enfin, des modèles prédictifs ont été établis, constituant un outil pertinent pour la surveillance, la maintenance proactive et l’optimisation des convertisseurs GaN en environnements embarqués.

Power converters based on gallium nitride (GaN) are progressing swiftly owing to their exceptional efficiency and tiny dimensions, boosted by high power density and fast switching capabilities. Nevertheless, these benefits are accompanied by considerable thermal management issues that impact reliability, performance, and operational lifespan. This review examines advanced thermal management approaches for high-power-density GaN power converters, including active and passive cooling technologies, sophisticated packaging designs, and the use of novel materials like graphene and diamond to improve heat dissipation. The impacts of thermal boundary resistance, self-heating phenomena, and substrate selection on thermal performance are thoroughly analyzed. Strategies for enhancing printed circuit board (PCB) layouts, thermal vias, and the use of thermal interface materials (TIMs) are also emphasized. The study highlights co-design approaches that optimize thermal resistance and layout efficiency, supporting GaN operation under high-frequency conditions. This thorough investigation offers insights into addressing the thermal challenges linked to GaN technology, promoting its adoption in forthcoming power devices.