A new technique for measuring the thermal conductivity of thin films has been developed, described as the Circular Heat Source (CHS) method. While there are some limited existing capabilities at a research level for measuring thermal conductivity (e.g. 3-Omega method), thin films are generally challenging to characterize with standard methods commercially available.
A new type of sensor system is presented specifically targeted towards the field of thermal conductivity measurement of thin films and coatings. A theory of operation to the CHS method for thermal conductivity characterization of thin films is to be presented. The temperature fields created by a circular heat source (CHS) are derived for the case of a CHS embedded inside two identical semi-infinite media, when different thermal contact resistances (CRs) are present on each surface of the CHS.
Three different temperature fields are derived: the temperature on the CHS surface and in each one of the media surrounding the CHS. The derivation of the 3-dimensional heat flow solution uses first principles with no assumptions. It employs the Hankel and Laplace transforms. Although the analytical solution presented here is exact with no approximations, it is given in an integral form, which requires numerical evaluation. The application of the solution to thin film thermal conductivity measurements is demonstrated. Finite element simulations performed in COMSOL Multiphysics are provided and compared with the analytical solution. Regressions of the COMSOL data show an excellent match between the actual and theoretically-predicted CR, which is readily translated into the thermal conductivity of the thin film.