Bridging Finite Element and Molecular Dynamics for Non-Fourier Thermal Transport Near Nanoscale Hot Spot

Abstract: Nanoscale hot spots forming tens of nanometers beneath the gate in advanced FinFET and HEMT devices drive heat transport into a non-Fourier regime, challenging conventional (Fourier-based) finite-element (FEM) analyses and complicating future thermal-aware chip design. Molecular dynamics (MD) naturally captures ballistic transport and phonon nonequilibrium, but has not been applied to hot-spot problems due to computational cost. Here, we perform the first MD simulations of hot-spot heat transfer across ballistic-diffusive regimes and benchmark them against FEM. We find that FEM using bulk thermal conductivity $κ0$ significantly underestimates hot-spot temperature, even when the channel thickness is ~10 times the phonon mean free path, indicating persistent non-Fourier effects. We introduce a size-dependent "best" conductivity, $κ{\mathrm{best}}$, using which FEM can reproduce MD hot-spot temperatures with high fidelity. We further decompose the MD-extracted thermal resistance into: (i) diffusive spreading, (ii) cross-plane ballistic, (iii) heat-carrier selective heating, and (iv) residual 3D ballistic-spreading resistances, and quantify each contribution. The resulting framework offers a practical route to embed non-Fourier physics into FEM for hot-spot prediction, reliability assessment, and thermally aware design of next-generation transistors.