Interfacial Thermal Resistance: From Fundamental Insights to Engineering

Abstract

The design of effective thermal management solutions for devices at the nanoscale relies on our fundamental understanding of heat transport across interfaces, which dominates the device thermal resistance. This talk will cover some recent insights on how the broadband spectrum of interacting heat carriers (phonons) crosses single or multiple interfaces, and how these insights may be used to tune the interfacial thermal resistance. Unlike bulk crystals, where defects and disorder increase the thermal resistance, these imperfections could cause the opposite effect on interfacial resistance. For instance, adding interatomic mixing to a perfect, lattice matched interface can decrease the resistance 20%. The random mixing relaxes symmetry constraints on phonons crossing the interface, thus opening more transport channels to carry heat. Similarly, adding a thin intermediate layer at the interface can decrease the interfacial resistance, contrary to bulk crystals where resistance is proportional to sample length. In this case, phonon-phonon interactions within the intermediate layer allow energy relaxation of phonons and open more heat transport channels. The interfacial resistance of this system can be minimized by choosing the “impedance” of the intermediate layer as the geometric mean of the “impedances” of the materials composing the interface. This result extends to a compositionally graded interfacial layer with an exponentially varying impedance that generates the thermal equivalent of a broadband impedance matching network. When the layer added at the interface is ultra thin, the total interfacial resistance can be split into three resistances in series. One depends on coherent wave transmission across the interface, while the other two arise from the thermalization of the non-equilibrium phonons in the vicinity of the interface. This research is supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division.