Measurement of the thermal diffusivity of metallic thin films: Sn, Mo, and Al0.97Ti0.03 alloy

The thermal diffusivity of Sn, Mo, and Al0.97Ti0.03 alloy thin films which are commonly used in MEMS (micro electro mechanical systems) applications is measured by the AC calorimetric method. The results show that the thermal diflusivity values of the thin films are generally lower that those of the bulk materials. Especially, the Al0.97Ti0.03 thin film shows a pronounced thermal conductivity drop due to impurity scattering. The electrical conductivity values of the thin films are also measured by the standard four-probe technique. The variation of thermal and electrical conductivities follows the Wiedmann-Franz law in the case of Sn film. However, the reduction of thermal conductivity is found to be much smaller than that of electrical conductivity in the case of Al0.97Ti0.03 and Mo. In addition to the AC calorimetric method, the photothermal mirage technique is also employed to measure the thermal diffusivity. The results demonstrate that the mirage technique can be used to measure the thermal diffusivity in a non-contact way though the uncertainty is relatively large because of the difficulty in optical alignment and temperature increase during the measurement.