ICT2014 Abstracts

Recently, nanostructured thermoelectric materials, such as superlattices and nanocrystalline materials, have shown to be able to decrease the lattice thermal conductivity caused by phonon scattering at the superlattice interfaces or grain boundaries, and then enhance their ZT. Hence, the investigation of phonon scattering, i.e., thermal transport, is one of the key factors in nanostructured thermoelectric materials. To investigate the thermal transport of the nanostructured materials, thin films obtain many advantageous characteristics such as easily controlling the grain sizes, creating nano-porous structures and fabricating nanoparticle compounds. As a result, the measurement technique for thermal conductivity of thin films is the fundamental factor to advance the understating of thermal transport as well as the enhancement of thermoelectric performance.

To date, a number of the measurement techniques (e.g., 3w method, ac calorimetric method and thermoreflectance method) have been proposed. Among them, 3w method is widely used because the measurement system is very simple, and is not required expensive equipment. For the thermal conductivity measurement of thermoelectric thin films using the 3w method, it is needed to prepare a dielectric thin film and a metallic thin wire on a thermoelectric thin film. In this case, the thermal contact resistance between the thermoelectric thin film and dielectric thin film has an effect on the estimation of thermal conductivity. Therefore, the estimation of thermal contact resistance is crucial to determine the precise thermal conductivity of thermoelectric thin films using 3w method.

In this study, we prepared nanocrystalline bismuth-telluride based thin films with various film thicknesses by sputtering method. The temperature amplitude of the each sample was measured by using the 3w method at room temperature. By the analysis of film thickness dependence of temperature amplitude, the total thermal resistance of each sample was divided the thin film contribution into the interface contribution (thermal contact resistance). Finally, we estimate the thermal conductivity of the nanocrystalline bismuth-telluride based thin films without the contribution of the thermal contact resistance.