Unusually high thermal conductivity in diamond films

Chemical-vapor-deposited (CVD) polycrystalline diamond films have recently been reported with a thermal conductivity that is only 25% less than that of high quality single-crystal natural diamond. By studying a series of such films of various thicknesses grown under virtually identical conditions, we have discovered a significant (factor of four) through the thickness gradient in thermal conductivity. The observed gradient is attributed mainly to phonon scattering by the roughly cone-shaped columnar microstructure. For 350 μm films, the material near the top (growth) surface has a conductivity of at least 21 W/cm °C, i.e., comparable to the best single crystals. This remarkable dependence of thermal conductivity on microstructure has important implications for thermal management of microelectronic devices using CVD diamond.