Strain-driven anomalous thickness dependence of interfacial thermal conductance between dissimilar metals

Understanding thermal transport behaviors across dissimilar metal films is essential for optimizing electronic devices' performance and efficiency. However, the effect of interfacial parameters such as the thickness on interfacial thermal conductance (G) of metal/metal remains elusive. In this Letter, the G between Al and Cu with varying Cu thickness was investigated from 78 to 295 K using the time domain thermoreflectance technique combined with nonequilibrium molecular dynamics (NEMD) simulations and the diffuse mismatch model (DMM). The temperature dependence of G_Al/Cu follows a pattern that is consistent with phonon-related thermal transport behaviors and decreases with increasing Cu thickness. The phonon related behaviors are attributed to the existence of the oxide layer at the interface. By taking the oxide layer into account, NEMD and DMM calculations match well with the experimental results, proving that the oxide layer hinders electron transport across the interface. We further find that strain distributions in Cu layers have a negative correlation with Cu thickness. When applying compressive strain on Cu, the overlap of phonon density of states between Cu and Al increases, especially for phonons of 6.5-9 THz, which is responsible for the Cu thickness-dependence in G_Al/Cu. Our results not only help revealing strain effect on G but also pave the way for the thermal design of metal interconnect in integrated circuits.