Cross-scale Raman thermometry: Bridging equilibrium-to-non-equilibrium thermal dynamics from micro-devices to single-molecule junctions

Unprecedented heat flux densities arising from the relentless miniaturization and stacked packaging of micro/nano-electronics in the post-Moore’s Law era create a critical thermal bottleneck. While precise measurement of localized and interlayer temperatures in complex architectures is imperative, conventional metrology remains limited by the diffraction limit and invasiveness, failing to reach the sub-nanometer scale. Raman thermometry, a premier non-contact tool, addresses this challenge by probing phonon dynamics across length scales. This review establishes a comprehensive framework for cross-scale Raman thermometry, bridging equilibrium dynamics (micro-devices) to non-equilibrium energy statistics (single-molecule junctions). We first elucidate the fundamental principles of Raman thermometry, including intensity ratios, peak shifts, and linewidth broadening. We then trace the technological evolution from far-field micro-Raman mapping of hotspots to near-field techniques, surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS), that achieve deep nanoscale resolution. We emphasize the single-molecule frontier, where the classical definition of temperature breaks down, giving way to non-equilibrium energy statistics governed by quantum fluctuations. Finally, we address the inherent challenges of overcoming intrinsic performance limits and multi-physics decoupling, and envision an artificial intelligence (AI)-empowered paradigm for high-fidelity thermal characterization and inverse design in future electronics.