Thermal conductivity of CVD diamond films: high-precision, temperature-resolved measurements

Abstract

We describe a high-precision measuring system for the determination of the in-plane thermal conductivity of CVD diamond samples at temperatures between 77 and 900 K. The thermal conductivity is determined by establishing a well-defined steady-state heat flux through a diamond bar and by measuring the temperature gradient, using an array of eight thermocouples. The heat is supplied by a meander-shaped microheater located at one edge of the bar. By measuring the temperature distribution without heat production in the microheater, radiation losses are detected and corrected for. At room temperature the in-plane thermal conductivity of polished CVD diamond samples is determined with an accuracy better than 1%. A variety of CVD diamond samples deposited by microwave plasma CVD under different growth conditions was investigated. Some of the samples showed extraordinarily high thermal conductivities of up to 54 W cm −1K −1 at −150 °C. To our knowledge, this is the highest value reported so far for CVD diamond. The temperature dependence of the thermal conductivity is well described by Callaway's theory. By fitting theoretical curves to the experimental values, information about defect densities and grain boundaries is derived.