In-plane thermal conductivity measurement of nanoscale thin films via frequency-domain thermoreflectance with multilayer stacking

Nanoscale thin films are a fundamental building block of modern electronic and spintronic devices, and accurate characterization of their heat transport properties is essential for reliable design. However, measuring the in-plane thermal conductivity of substrate-supported nanoscale films remains difficult due to limited measurement sensitivity. This study introduces an approach that enables such measurements by integrating frequency-domain thermoreflectance (FDTR) with a multilayer stacked structure in which the target film and an interlayer are alternately deposited. This configuration increases the cumulative in-plane heat flow through the target layers while preserving the nanoscale thickness of each individual film. Using a fitting procedure that constrains identical parameters within the stack to shared values, the FDTR response becomes strongly sensitive to the in-plane thermal conductivity of the target film. The method is validated using a theoretical FDTR model. For instance, a 10 nm titanium film with a thermal conductivity of 16.8 W/(m K)—a case in which conventional FDTR yields insufficient sensitivity—exhibits an 11.5-fold enhancement in maximum sensitivity and a reduction in uncertainty to 13.6% when 30 stacked repetitions are used. Additional calculations for films with varying thicknesses and materials demonstrate that the method is suitable for nanoscale films commonly employed in devices, with thermal conductivities from 1 to 100 W/(m K) and thicknesses from 1 to 100 nm. This approach provides a practical and scalable means to experimentally evaluate in-plane thermal transport in nanoscale thin films and supports improved understanding of their thermal behavior in device applications.