Development of Differential Thermal Resistance Method for Thermal Conductivity Measurement Down to Microscale

The thermal conductivity ( k ) of materials plays a critical role in the effectiveness of devices in the engineering fields. In this work, a novel differential thermal resistance (DTR) method is developed to measure the out-of-plane and in-plane k of mm- down to mu m-thick samples. Traditional techniques for direct k measurement usually needs measuring the heat transfer and temperature difference across the sample. The DTR technique rather constructs configurations for reference samples and sample of interest to measure the temperature rise and determine the thermal resistance of the sample and its k . Non-contact heating by laser and thermal probing by a high-sensitivity infrared camera are employed. The out-ofplane k of 1.49 and 2.81 mm-thick acrylic samples, and 1 mm-thick glass slide is measured to be 0.20, 0.19, and 1.27 W center dot m -1 center dot K -1 , respectively. The in-plane k of a 26 mu m-thick graphene paper is measured to be 616 W center dot m -1 center dot K -1 . A good level of agreement is obtained between our measurement results and reference values. Moreover, the in-plane k of 15 mu m-thick pure copper foil is measured to be 322 W center dot m -1 center dot K -1 , very well agreeing with the density-adjusted value of 326 W center dot m -1 center dot K -1 for pure copper. Also by measuring the copper coil's electrical conductivity, we are able to determine its Lorenz number as (2.21-2.30) x 10 -8 W center dot ohm center dot K -2 which agrees well with reference values of (2.23-2.33) x 10 -8 W center dot ohm center dot K -2 . (c) 2022 Elsevier Ltd. All rights reserved.