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 κ local ⊥ rising more rapidly with z than κ local a 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.