Accurate measurements of cross-plane thermal conductivity of thin films by dual-frequency time-domain thermoreflectance (TDTR)

作者：Jiang Puqing; Huang Bin; Koh Yee Kan^*

来源：Review of Scientific Instruments, 2016, 87(7): 075101.

DOI：10.1063/1.4954969

Accurate measurements of the cross-plane thermal conductivity Lambda(cross) of a high-thermal-conductivity thin film on a low-thermal-conductivity (Lambda(s)) substrate (e.g.,Lambda(cross)/Lambda(s) > 20) are challenging, due to the low thermal resistance of the thin film compared with that of the substrate. In principle, Lambda(cross) could be measured by time-domain thermoreflectance (TDTR), using a high modulation frequency f(h) and a large laser spot size. However, with one TDTR measurement at f(h), the uncertainty of the TDTR measurement is usually high due to low sensitivity of TDTR signals to Lambda(cross) and high sensitivity to the thickness h(Al) of Al transducer deposited on the sample for TDTR measurements. We observe that in most TDTR measurements, the sensitivity to h(Al) only depends weakly on the modulation frequency f. Thus, we performed an additional TDTR measurement at a low modulation frequency f(0), such that the sensitivity to h(Al) is comparable but the sensitivity to Lambda(cross) is near zero. We then analyze the ratio of the TDTR signals at f(h) to that at f(0), and thus significantly improve the accuracy of our Lambda(cross) measurements. As a demonstration of the dual-frequency approach, we measured the cross-plane thermal conductivity of a 400-nm-thick nickel-iron alloy film and a 3-mu m-thick Cu film, both with an accuracy of similar to 10%. The dual-frequency TDTR approach is useful for future studies of thin films. Published by AIP Publishing.

• 出版日期2016-7