Decoupling Thermal Properties in Multilayer Systems for Advanced Thermoreflectance Techniques

Thermoreflectance techniques, including time-domain thermoreflectance (TDTR), frequency-domain thermoreflectance (FDTR), and the square-pulsed source (SPS) method, are powerful tools for characterizing the thermal properties of bulk and thin-film materials. However, accurately interpreting their signals remains challenging due to intricate interdependencies among experimental variables. This study introduces a systematic framework based on singular value decomposition (SVD) to decouple these interdependent parameters and enhance the reliability of thermal property extraction. By applying SVD to the sensitivity matrix, we identify key parameter combinations and establish essential dimensionless numbers that govern thermoreflectance signals. The framework is applied to a GaN/Si heterostructure, where the performance of TDTR, FDTR, and SPS is evaluated and compared. The results demonstrate a high degree of consistency across all three techniques. Notably, with the intricate relationships of parameters unraveled, TDTR, FDTR, and SPS demonstrate significant potential to simultaneously and accurately extract five to seven key thermal properties, including thermal conductivity, heat capacity, and interfacial thermal conductance of the GaN/Si multilayer system. This framework not only improves the precision of thermoreflectance measurements but also lays a foundation for advanced thermal metrology in research and industrial applications.