Thermal Conductivity Measurement of Cu Thin Films using Radiation Heat Exchange Method
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1022-II06-07
Thermal Conductivity Measurement of Cu Thin Films using Radiation Heat Exchange Method Sang Ryu1, Youngman Kim1, and Woonam Juhng2 1
Materials Science & Engineering, Chonnam Natioal University, 300, YongBong-Dong, Buk-Gu, Gwangju, 500-757, Korea, Republic of 2
Mechanical Engineering, Chonnam National University, 300, YongBong-Dong, BukGu, Gwangju, 500-757, Korea, Republic of
Abstract
A measurement method of thermal conductivities of Cu thin films was devised from the temperature distributions of substrate surfaces. The substrate was prepared to have a prismatic bar shape, and was deposited with Cu thin films using sputtering. Two metal coated surfaces of specimens were brought into contact to maintain the insulated boundary condition. Specimens were heated with constant temperature at both ends. The temperature distributions were measured from the back surface of substrate using a radiation thermometry.
The thermal conductivities of Cu thin films were found to be much lower than those of bulk materials. Wiedemann-Franz law could be applied to thin films produced in this study. Thermal conductivity was also estimated from the resistivity of thin film and Lorenz number of bulk material.
Keywords: thermal conductivity; thin film; radiation heat exchange.
1. INTRODUCTION A few methods have been developed for thermal conductivity measurement of a thin film on a substrate. Boyce et.al.1 used a technique to pass an electric current along the film, thus creating a temperature gradient, and deduce the thermal conductivity from the measured change in resistance with time. Wieczorek et.al.2 obtained thermal conductivity from the total rise of temperature at the film surface and the rise of temperature of the bare substrate with uniform heat flux on each limited surface. The photo-acoustic method was applied to the measurement of thermal properties of thin films on substrates, which has been used for spectroscopy3. Pico-second transient thermo-reflectance technique was used to determine the thermal diffusivity of metallic film4. Above two methods are non-contacting and nondestructive to a film and independent of thermal properties of a substrate. In this paper, radiation heat exchange method5 was applied to the measurement of thermal conductivity of Cu thin film on a substrate. The advantages of the radiation heat exchange method are; i) the measurement method and apparatus are relatively simple, ii) specimens need not altered and there are no disturbances of temperature distribution. This method requires the pre-knowledge of thermal conductivity of the substrate. Theoretical analyses of the temperature distribution were performed in two-layered composite material with radiation heat exchange on the surface.
We developed the
equation which gave the thermal conductivity of a sample from the temperature distribution on the surface of the substrate. Temperature measurements were carried out for sputtered Cu films on borosilicate glass to get thermal conductivity of Cu thin films eventually.
2. THEORY 2.1.
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