Articles techniques et présentations

Gallium nitride (GaN)-based power devices have emerged as leading contenders for high-frequency applications owing to their inherent robustness, high power density and superior electron mobility. [1] They are now essential components in radar systems, cellular base stations, and next-generation communication networks. However, commercial GaN devices have struggled to keep pace with increasing power demands, typically achieving up to 8 W/mm due to limited thermal management capability under high power dissipation, resulting in elevated peak channel temperatures. [2]

To address this, diamond can be incorporated as a heat spreader between the SiC substrate and heat sink to exploit its exceptional thermal conductivity, thereby reducing channel temperature and increasing allowable power dissipation. This work presents the thermal modelling of commercial GaN-on-SiC RF devices in COMSOL Multiphysics 6.3 with diamond heat spreaders.

The device geometry was first imported from 2D DXF layouts using discrete work planes and extruded into a full three-dimensional structure. The thermal stack is shown in Figure 1. A meshing strategy with strong gate-channel refinement using a combination of boundary, edge, and swept meshes was implemented to accurately resolve steep thermal gradients in the active region (see Figure 2). Power dissipation was represented as a volumetric heat source positioned at the drain-side gate edge, while a constant-temperature boundary condition was applied at the baseplate to represent the heat sink. An example temperature distribution is shown in Figure 3.

The Heat Transfer in Solids and Events interfaces were used to investigate both continuous-wave and pulsed operation. Extensive parametric studies examined the influence of thermal boundary resistance at the GaN-SiC boundary, implemented using a thin-layer approximation, as well as die-attach properties, diamond thickness and diamond thermal conductivity on device thermal performance.

The simulations identified the key parameters required to fully utilise diamond and provided a framework for Space Forge in the development of diamond-based heat spreaders. For large-periphery devices, a diamond heat spreader enabled up to a 33 % increase in allowable power dissipation relative to CuW at a peak channel temperature limit of 220 °C, typical for non-space applications.

Overall, this work demonstrates how COMSOL Multiphysics can be applied to real-world thermal engineering challenges to push the performance limits of GaN RF devices and support their continued advancement towards higher-power operation.