Maximizing the Thermal Hotspot Reduction by Optimizing the Thickness of Multilayer Hbn Heat Spreader

This article investigates the thickness-dependent heat spreading performance of multilayer hexagonal boron nitride (hBN). The growth by a cold-wall chemical vapor deposition system results in large-area and high crystal quality of multilayer hBN. The full width at half maximum of Raman E2g peak is approximately 25 cm-1 and the bandgap is larger than 5.8 eV. Varying the growth duration from 5 to 15 min on Ni foil results in hBN thicknesses of 5-12 nm with comparable crystal quality. The electrothermal analysis using a sensitive Pt/Cu/Ti micro-coil introduces the figure of merit (FoM) of hBN as an insulator heat spreader. Fittings on FoM plots suggest that multilayer hBN with a thickness of-2 nm is optimum for a 25% reduction in the thermal hotspot. The initial drop in lateral thermal resistance is significant for a few nanometers-thick hBN, where a 22.5% reduction is measured from the 5.6 nm-thick hBN heat spreader. Further thickening of hBN reduces the lateral thermal resistance by approximately 0.37% nm-1. Findings from this work provide a significant contribution to the implementation of hBN as a direct contact heat spreader on the actual power devices.