Thermal conductivity of CVD diamond: Methods and results

Following constant improvement in the synthesis methods of diamond in metastable conditions by chemical vapour deposition, it is nowadays possible to grow polycrystalline diamond with thermal conductivities of over 20 W K^-1 cm^-1. This gives rise to applications of this material in the thermal management of components in optronics and microelectronics. Reliable, precise thermal characterization methods are therefore needed. However, measuring the thermal conductivity of CVD diamonds is a non-trivial task: the high conductivity makes it difficult to establish a measurable thermal gradient and furthermore, the different experimental setups are differently sensitive to the particular polycrystalline structure of the layers. A recent round-robin test revealed considerable differences in the values measured using the different techniques. In this paper the principal measuring methods for the thermal conductivity of CVD diamonds are reviewed and compared. Then the influence of the microstructure on the thermal properties as well as the correlations with the presence of impurities and crystal defects detected by Raman and luminescence spectroscopy are discussed.