Thermal conductivity measurement of transparent thin film by photothermal heating with continuous wave laser

Abstract

Optical methods using lasers to extract thermal conductivities including frequency-domain thermoreflectance, time-domain thermoreflectance, and laser flash methods require either pulse lasers or frequency modulated lasers to heat samples. In contrast, we recently developed a thermal conductivity measurement scheme based on quantitative phase microscope (QPM) where a heating laser can be a continuous (CW) laser. The use of CW laser simplifies the optical system. Additionally, our method has an advantage to extract thermal conductivity and thermo-optic coefficient (TOC) simultaneously. In terms of the fitting model of our method, so far it was limited only for transparent substrate. In the current work, we experimentally show that with the modified fitting model, our system can measure the thermal conductivity and TOC of a transparent film on a transparent substrate. A measurement result for an indium gallium zinc oxide (IGZO) thin film deposited on a glass substrate is presented as an example.