Thermal Transport in Metallic Thin Films and Superlattices: Influence of Interfaces and Microstructure

Moore’s law continues to push device dimensions into the nanometer regime, leading to elevated power densities and localized heating. At these length scales, interconnects have become a critical bottleneck, as their electrical and thermal properties degrade at reduced dimensions. Copper, the industry-standard interconnect, faces challenges such as thermochemical and thermomechanical instability, along with a sharp rise in resistivity when interface and grain boundary characteristic length scales reduce to below those of the electron mean free path. As very-large-scale integration nodes shrink below 5 nm, alternative metals such as ruthenium, cobalt, molybdenum, and iridium are being explored for their higher cohesive energies, integration compatibility, and shorter intrinsic electron mean free paths, which reduce sensitivity to boundary scattering and help preserve conductivity. At these scales, heat and charge transport are governed by complex interactions among electrons, phonons, defects, and interfaces. Classical models such as Matthiessen’s rule and the Wiedemann–Franz law encounter limitations, as they remain unvalidated, when multiple scattering mechanisms coexist or when phonon contributions become significant. Phonon-mediated transport, in particular, remains insufficiently understood in ultrathin metals and multilayer systems. Beyond CMOS interconnects, transition metal carbide and nitride superlattices offer new opportunities to engineer thermal and mechanical performance through interface design. Their moderate thermal conductivity and high stiffness make them attractive for microscale systems and extreme environments, where improved interface quality can enhance phonon transport and boost elastic modulus. In this dissertation, I investigate nanoscale thermal and electrical transport in both emerging interconnect metals, metal–metal and metal nitride–carbide superlattices. I integrate advanced experimental techniques with physics-based modeling to evaluate electron and phonon contributions to heat transfer. My work examines the validity of classical transport models and explores how interface quality, strain, and microstructure affect phonon thermal conductivity and elastic modulus. This research identifies materials optimized for next-generation interconnects and applications requiring both high thermal efficiency and stable elastic modulus. This work aims to inform the design of materials that combine high thermal performance with optimized mechanical properties, such as elastic modulus, for a wide range of advanced technologies.