Technical Assessment of Thermal Management Techniques for GaN Power Transistors: Heat Spreaders

Gallium Nitride High Electron Mobility Transistors (GaN HEMTs) enable higher efficiency, higher power density, and more compact passive components resulting in lighter, smaller, and more efficient power electronic systems for transportation electrification applications as opposed to conventional Silicon (Si) based devices. The industry is actively embracing GaN HEMTs for 22 kW or higher power systems, particularly in power density-oriented applications such as electric vehicles (EVs). This preference is driven by the remarkable figures of merit exhibited by GaN HEMTs, surpassing those of conventional Si devices. Thermal considerations as well as circuit parasitic components in high power density GaN-based applications play a significant role in achieving overall performance. This article explores a cooling approach that utilizes a copper heat spreader to enhance heat transfer capability, as well as its potential impact on the stray capacitance between the GaN transistor substrate and heat sink. After evaluating the properties of various thermal interface materials (TIMs), this article addresses the challenges involved in implementing a cooling fixture for GaN transistors and offers potential solutions. Computational Fluid Dynamics (CFD) simulations and experiments are performed to verify the thermal and electrical performance. Test results show that with the applied method the thermal resistance between the GaN transistor case and its ambient surroundings through the heat sink can be reduced up to 30% while keeping the same stray capacitance value.