Abstract

Diamond has been a promising material for heat spreading applications in a variety of high-power electronic devices such as AlGaN/GaN high electron mobility transistors (HEMTs) due to its high thermal conductivity. However, diamond thin-film deposition by chemical vapor deposition (CVD) often creates highly defective and small grained regions near the growth interface with the substrate (often Si), which severely impair heat conduction through the diamond and into the underlying substrate. The assessment of thermal properties of CVD diamond films is challenging primarily due to the nonhomogeneity and anisotropy in this defective region, which complicates data interpretation using both electrical and optical characterization methods.

This presentation reports measurements of thermal conduction in nanocrystalline diamond films with thicknesses near 1 μm on Si using pump-probe time-domain thermoreflectance (TDTR). We use multiple pump modulation frequencies and a combination of amplitude and ratio thermoreflectance signals to determine the cross-plane and in-plane thermal conductivities of the diamond and the thermal boundary resistance at the interface between the diamond and Si. Scanning electron microscopy and other characterization methods probe the microstructural quality of each diamond film including the in-plane grain size and concentrations of defects and impurities. While this study is focused on only one candidate substrate, the methodology developed here supports characterization of diamond composites with a variety of materials including silicon carbide and gallium nitride for applications in high-power electronics.