Analysis of ballistic thermal resistance in FinFETs considering Joule heating effects

The continued miniaturization of integrated circuits has significantly increased power density in heterostructure transistors, creating localized hotspots that degrade device performance. Conventional Fourier's Law (FL) models are limited, particularly when device dimensions approach the phonon mean free path. To address this, we employ the Discrete Ordinates Method (DOM) to solve the non-gray Boltzmann Transport Equation (BTE), enabling precise thermal analysis in FinFETs. Our study underscores the need to incorporate ballistic phonon effects for accurate hotspot temperature predictions under self-heating conditions. Specifically, BTE based temperature estimates are up to 10 % higher than FL based predictions, underscoring the importance of capturing phonon ballistic transport. In heterostructure transistors, substrate-based heat dissipation remains the primary cooling route. Our research demonstrates that diamond substrates can reduce total thermal resistance by approximately 25 % compared to germanium, yet they exhibit higher interfacial thermal resistance relative to silicon carbide and germanium. This work elucidates how substrate thickness, heat-source size, and substrate material critically influence ballistic thermal resistance, thus offering valuable theoretical guidance for optimizing FinFETs design and enhancing thermal management.