SiC films could outstrip diamond
Researchers in Japan have shown that the thermal conductivity of thin films of cubic 3C-silicon carbide can be higher than diamond (writes Nick Flaherty).
The team, led by Associate Professor Jianbo Liang and Professor Naoteru Shigekawa at the Osaka Metropolitan University Graduate School of Engineering, used thermal conductivity evaluation and atomic-level analysis in their research.
First, they grew 3C-SiC bulk crystals on a silicon substrate and showed a thermal conductivity of 500 W/mK, which is second only to diamond. Then they grew a thin film of 3C-SiC crystals 1.75 microns thick, which exhibited a thermal conductivity higher than that of diamond.
3C-SiC is a SiC polytype that can be epitaxially grown on silicon, and the 3C-SiC-Si thermal boundary conductance is among the highest for semiconductor interfaces. This suggests that thin-film 3C-SiC could be used in active components as well as substrates for power electronics.
“Both the freestanding 3C-SiC crystal and thin films on a silicon substrate have this high thermal conductivity, and we expect large-diameter wafers could be fabricated at a low cost,” Prof Liang said. “That should lead to improved heat dissipation on a practical level in electronic devices.”
The results resolve a long-standing puzzle that the literature values of thermal conductivity for 3C-SiC are lower than the structurally more complex 6H-SiC. The high thermal conductivity arises from the high purity and crystal quality of 3C-SiC crystals, which avoids the defects that scatter the phonons that carry the thermal energy away.
The atomic-level analysis allowed the team to investigate why they were able to measure such high thermal conductivity, which had not been previously observed. They found that the 3C-SiC crystal contained almost no impurities: the atoms in the crystal were regularly arranged, indicating a very high-quality single crystal.