Modulated thermoreflectance imaging of hidden electric current distributions in thin-film layered structures

Abstract

Thermal imaging of hidden electric current distributions with a resolution of several ten micrometers is demonstrated. It is shown that the thermoreflectance technique is capable of monitoring current-induced temperature variations on as well as beneath the surface of thin layered structures. A temperature pattern was generated by Joule heating using an ac current in a 2.5 μm thick structured gold film that was evaporated on a glass substrate and covered by a TiOx layer. The current density distribution in the gold film is revealed by the measured photothermal pattern, provided that both laser beam diameter and thermal diffusion length are smaller than the desired lateral resolution.