Cross-plane heat conduction in thin solid films

TL;DR

This paper introduces a fast semi-analytical method to solve the Boltzmann transport equation for cross-plane heat conduction in thin films, covering diffusive to ballistic regimes with frequency-dependent phonon properties.

Contribution

The authors develop a semi-analytical series expansion approach that is significantly faster and more accurate than previous numerical methods, providing explicit thermal conductivity expressions.

Findings

Method is over three orders of magnitude faster than prior approaches.

Provides a simple analytical expression for thermal conductivity as a function of film thickness.

Enables more accurate modeling of heat conduction in thin films.

Abstract

Cross-plane heat transport in thin films with thickness comparable to the phonon mean free paths is of both fundamental and practical interest. However, physical insight is difficult to obtain for the cross-plane geometry due to the challenge of solving the Boltzmann equation in a finite domain. Here, we present a semi-analytical series expansion method to solve the transient, frequency-dependent Boltzmann transport equation that is valid from the diffusive to ballistic transport regimes and rigorously includes frequency-dependence of phonon properties. Further, our method is more than three orders of magnitude faster than prior numerical methods and provides a simple analytical expression for the thermal conductivity as a function of film thickness. Our result enables a more accurate understanding of heat conduction in thin films.