Effect of film thickness on the temperature dependence of thermal conductivity for diamond/BeO composites

Polycrystalline diamond films of different thickness have been deposited on the surface of beryllium oxide (BeO) substrates by hot filament chemical vapor deposition (CVD). Thermal conductivity (κ value) of various samples has been measured. The biggest increase of 17.5% in thermal conductivity relative to the substrate is obtained in the composite with 5.0 μm film at room temperature. The temperature dependence of the thermal conductivity for the composites with films of different thickness has been investigated. Comprehensive effect of film purity and residual stress is found to be responsible for the variation of temperature dependence for the composites. Stress-induced defects play an important role in the thermal conductivity at high temperature from our analysis. This work is of great significance on the preparation and thermal application of composites with CVD diamond in such a film/substrate structure.