Photoacoustic characterization of thermal transport properties in thin films and microstructures

Abstract

Photoacoustic measurements have been performed on selected metallic and dielectric thin film-substrate systems. These can also yield spatial information about microstructures. By using the depth profiling option of this measuring technique the thermal properties of the film and also the thermal contact resistance between film and substrate can be determined. It can be shown that the thermal conductivity of the thin films under investigation is strongly reduced compared with the corresponding bulk value. This strong reduction is a result of the particular morphology of the films, i.e. small grain size, amorphousness and high concentration of foreign atoms and defects depending on the deposition parameters. In microstructures, additional reduction can be observed by size effects which are due to the specific geometry of the structure. Sputtered films of Au, TiN, Al 2O 3 and electroplated films of Ni on different substrates have been studied. In the case of the Ni and TiN films it could be shown that the thermal contact resistance is correlated with the adhesion strength of the films measured by a conventional scratch test.