Thermal conductivity and the microstructure of state-of-the-art chemical-vapor-deposited (CVD) diamond

Abstract Two new techniques have been developed for making high-accuracy measurements of the thermal conductivity κ in chemical-vapor-deposited (CVD) diamond films: (1) a steady state technique for measuring κ∥ (heat flowing in a direction parallel to the plane of the sample) and (2) a laser flash technique for measuring κ⊥ (heat flowing perpendicular to the plane of the film). By measuring κ∥ and κ⊥ for a series of high-quality CVD diamond films of different thicknesses, we are able to extract local values for these variables as a function of height z above the substrate surface. Both show a large gradient with respect to z, with κlocal⊥ rising more rapidly with z than κlocala for approximately the first 200 μm. This is consistent with phonon scattering from impurities and defects if they are preferentially located near grain boundaries of the columnar structure. For z ⪆ 300 μ m , the local conductivity is nearly isotropic with the very high value of 23–24 W cm−1°C−1 at 25°C, to be compared with 22 W cm−1°C−1 for the best type IIa single-crystal diamond so far reported. These results have direct implications for the thermal management of microelectronic devices if the remarkable conductivity of diamond is to be used most effectively.