Nonequilibrium Landauer approach for thermal interfaces

Thermal boundary conductance (TBC) is critical in thermal management of modern electronic devices, and the Landauer approach is the most widely method for predicting TBC due to its intuitive and transparent physics. However, a decades-old puzzle has been that many of the measured TBCs, such as those well characterized across Al/Si and ZnO/GaN interfaces, significantly exceed the Landauer approach prediction, or even its upper limit called the ”radiation limit”. Here, we identify that a key assumption used in the Landauer approach, that phonons are in thermal equilibrium at the interface, is generally invalid and contributes to the discrepancy. We show that the measurable
temperature for each individual mode is not their emitting temperature, and due to the nonuniform transmission functions, different phonon modes are driven into strong thermal nonequilibrium. Hence, we modify the Landauer approach to include these effects and name it the
”Nonequilibrium Landauer approach”. Using our approach on the Al/Si and ZnO/GaN interfaces gives 100% increases in TBC as compared to the original Landauer approach and can now well explain the experimental results.