Measurement of Thermal Diffusivity of Thin Film in Thickness Direction Using an Ordinary Dielectric Film as the Sensor

Accurate thermal parameters of thin films are beneficial for the engineering thermal design and thermal management of electronic devices to improve the operating stability and prolong service life. In this article, a novel method for measuring the thermal diffusivity of thin films is proposed based on the thermal pulse method (TPM) for mapping space charge distribution, whose thermal response current is strongly determined by the temperature profiles within thin film. A multi-layer thin film structure is adopted, in which the tested film layer is thermally coupled on the dielectric film substrate with thermal parameters known. The thermal pulse by laser pulse excites the tested film and then penetrates into the dielectric film substrate. By analyzing the thermal response current of the dielectric film substrate, one can deduce the temperature profiles in both layers and therefore the thermal diffusivity of the tested film. The proposed method can determine the thermal diffusivity of both insulating and electric conduction films with the thickness tens of micrometers in through thickness direction. The obtained values of the thermal diffusivity of polyimide (PI), bi-oriented polypropylene (BOPP), polyethylene 2,6-naphthalate (PEN), tin(Sn) foil, and lead (Pb) foil are well consistent with the data provided in the literatures. By the analyzing heat boundary conditions, the interface thermal resistance between the tested film and the dielectric film substrate can be also determined at the same time.