This paper describes ultrathin tantalum-based high-volumetric-density power capacitors with low leakage properties for 1-10-MHz frequency applications. Nanodielectrics with low-defect density were grown on nanoporous tantalum anodes using the self-limiting anodization process. The fundamental mechanisms that govern the film growth and quality were investigated to provide anodization process guidelines. Conducting polymer nanoparticles were used as the cathodes. Complete filling of conducting polymer was achieved by the optimization of conducting polymer application process. Energy dispersive spectroscopy and structural SEM studies were performed to investigate the morphology and structure of the tantalum pentoxide films. The fabricated capacitor showed 0.6-0.8 μF /mm2 of capacitance density in the 1-10-MHz range, in substrate-compatible ultrathin (<75μm) form factors. This is the highest volumetric density reported for such thin-film capacitors in a megahertz frequency range.