Thermal conductivity of thin films - Experimental methods and theoretical interpretation

The determination of the thermal conductivity of thin films is of great interest both for understanding the structure and conduction mechanism and for numerous technical applications of these films. The thermal conductivity lambda is a crucial term of the thermoelectric figure of merit z = alpha(2) sigma/lambda and consequently an important parameter for the design of thermoelectric thin film devices. Usually the film properties differ considerably from the bulk. Recently research activities are focused on thermoelectric thin film materials, since high z values can be expected in lowdimensional structures. Standard methods for the investigation of the Seebeck coefficient a and the electrical conductivity sigma are well established. However, measurements of the thermal conductivity of thin films are sofisticated and associated with various problems. New methods for the measurement of the thermal conductivity of thin films are reviewed. The problems of stationary and transient measuring techniques are discussed. The results are interpreted with models of surface scattering and grain boundary scattering of charge carriers and phonons.