Thermal properties characterization of conductive thin films and surfaces by pulsed lasers

摘要

An experimental system for investigation of thermal properties of thin films and material surfaces especially with high thermal conductivity was developed. This system is based on photothermal method using pulsed laser with nanosecond pulse duration in the UV range, and a high speed IR photodetector. Calibration of the experimental system, enabling absolute temperature measurement, is described. The system was calibrated for Cu, Al, Ti, Ni samples and Au/Ni layers on bronze substrates, where the mean sensibility of the detector varied from 31 μV/K for Cu and Au to 116 μV/K for Ti. First are shown measured thermal responses and deduced effusivities for pure metals in a 'bulk' form, which were investigated to validate the experimental accuracy of the system. Second, for a specific application of electrical contacts in microelectronics multilayer Au/Ni coatings on bronze substrates were studied. Thermal effusivity values plotted versus time after laser pulse enable estimation of the effusivity variation from the surface coating to the substrate. The effusivity of surface Au/Ni coatings with thickness 0.8/2 μm was estimated to 25 800 W s~(1/2) m~(-2)K~(-1) and with thickness 0.2/2 μm was estimated to 21 400 W s~(1/2) m~(-2) K~(-1).