Analysis of One-dimensional Heat Diffusion after Light Pulse Heating by the Response Function Method

To measure thermal diffusivity across thin films, the laser flash method has been improved by using ultrafast lasers and thermoreflectance temperature detection. These light pulse heating methods allow observation of one-dimensional heat diffusion from the heated face to the detected face of a specimen across a well-defined length of specimen thickness following the light pulse heating. Since most electronic devices, storage media, displays, and so forth have a multilayered structure of thin films, information about heat diffusion across multilayers, thermophysical properties of constituent single layers, boundary thermal resistance between the layers, and effective thermophysical properties of the multilayered structure as a whole are required for improved thermal design of devices and development of materials. To meet these requirements, a generally applicable approach to analyze one-dimensional heat diffusion across multilayers has been developed on the basis of the virtual heat source method and response function method. These methods of analysis can be applied over a timescale ranging from picoseconds, as observed by the picosecond thermoreflectance method, to more than 10 seconds, as observed by the laser flash method. (C) 2009 The Japan Society of Applied Physics