Thermal conductivity study of micrometer-thick thermoelectric films by using three-omega methods

Thermal conductivity is a key parameter of thermoelectric (TE) films. However, experimental reports on thermal conductivity of TE films are very limited due to the challenge in practical measurement. In this work, we report the use of some three-omega (3ω) methods to study the thermal conductivity of micrometer-thick Bi2Te3 TE films prepared by pulsed electroplating. The measurement devices are fabricated using sputtered SiO2 as dielectric layer and Au lines as heaters. The differential method and the slope method are separately used to determine the cross-plane thermal conductivity of the films. The characterization methods are demonstrated to be feasible and reliable from the reasonable changes of the 3ω voltage with frequency and thickness and the consistent measurement results using these two methods. The cross-plane thermal conductivity of the electroplated film is found to decrease from 1.8 Wm−1K−1 to 1.0 Wm−1K−1 as the pulse potential increases from −100 mV to 50 mV, which is attributed to the refined microstructure of the films. In addition, the thermal conductivity anisotropy of the Bi2Te3 film is evaluated by using a two-wire 3ω method and the factors contributing to the measurement uncertainty are discussed.