High‐Density Energy Storage in Si‐Integrated Dielectric Multilayers Through Interfacial Polarization and ML‐Guided Structural Optimization

Epitaxial dielectric thin films have attracted considerable attention for better energy storage performance than bulks and polymers, yet their reported recoverable energy density ( W rec ) commonly excludes the substrate, which limits its relevance to practical device‐level energy storage. Here, we develop a Si‐integrated BZT//S‐BZT multilayer capacitor to address this issue and simultaneously enhance polarization and breakdown strength ( E b ). By directly integrating the oxide multilayer on Si‐based substrates, the contribution of the substrate to the effective device volume is substantially reduced, enabling a realistic energy density ( W rec‐real ) of 105.51 J/cm 3 , exceeding that of the overwhelming majority of comparable systems. The BZT and S‐BZT sublayers exhibit small lattice mismatch but pronounced dielectric contrast, which induces strong interfacial polarization ( P inter ) without introducing interfacial structural perturbation. Landau–Ginzburg–Devonshire theory and phase‐field simulations consistently verify the interface‐induced polarization enhancement and agree well with the experimental observations. To further improve E b , machine learning was employed to establish the relationship between the multilayer structural parameters and E b and to identify the optimal starting‐layer thickness. Experimental results closely reproduce the predicted trend, leading to an optimized Big‐Mac‐ n architecture with a high W rec of 131.21 J/cm 3 and an E b of 6.5 MV/cm. The multilayer also exhibits excellent fatigue, frequency, and temperature stability, together with ultrafast discharge capability. This work establishes a data‐driven interface‐engineering strategy for reliable, Si‐integrated dielectric energy‐storage capacitors.