Direct measurement of in-plane thermal conductivity of microscale suspended thin films using a novel 3ω method

A novel 3ω method has been developed for measuring the in-plane thermal conductivity of microscale suspended thin films. In this method, a heating wire makes contact with the test film using Ampere's force with the assistance of an interstitial material. The thermal impedance is determined by comparing the triple-frequency voltages across the heating wire with and without contact with the test film. The thermal conductivity can be directly obtained from the slope of the real part of the thermal impedance plotted against the logarithm of the heating frequency, even when the thermal contact resistance between the heating wire and the test film is unknown. This method has been successfully applied to determine the in-plane thermal conductivity of various thin films, including stainless-steel and Kapton films. The linear relationship is significantly improved for samples with low thermal conductivity, and its accuracy is verified through repeated measurements under different contact conditions.