All-nanosheet ultrathin capacitors assembled layer-by-layer via solution-based processes

All-nanosheet ultrathin capacitors of Ru_0.95O₂ ^0.2-/Ca₂Nb₃O₁₀ ^-/Ru _0.95O₂ ^0.2- were successfully assembled through facile room-temperature solution-based processes. As a bottom electrode, conductive Ru_0.95O₂ ^0.2- nanosheets were first assembled on a quartz glass substrate through a sequential adsorption process with polycations. On top of the Ru_0.95O₂ ^0.2- nanosheet film, Ca₂Nb₃O₁₀ ^- nanosheets were deposited by the Langmuir-Blodgett technique to serve as a dielectric layer. Deposition parameters were optimized for each process to construct a densely packed multilayer structure. The multilayer buildup process was monitored by various characterizations such as atomic force microscopy (AFM), ultraviolet-visible absorption spectra, and X-ray diffraction data, which provided compelling evidence for regular growth of Ru_0.95O ₂ ^0.2- and Ca₂Nb₃O₁₀ ^- nanosheet films with the designed multilayer structures. Finally, an array of circular films (50 μm ?) of Ru_0.95O₂ ^0.2- nanosheets was fabricated as top electrodes on the as-deposited nanosheet films by combining the standard photolithography and sequential adsorption processes. Microscopic observations by AFM and cross-sectional transmission electron microscopy, as well as nanoscopic elemental analysis, visualized the sandwich metal-insulator-metal structure of Ru _0.95O₂ ^0.2-/Ca₂Nb₃O ₁₀ ^-/Ru_0.95O₂ ^0.2- with a total thickness less than 30 nm. Electrical measurements indicate that the system really works as an ultrathin capacitor, achieving a capacitance density of ∼27.5 μF cm^-2, which is far superior to currently available commercial capacitor devices. This work demonstrates the great potential of functional oxide nanosheets as components for nanoelectronics, thus contributing to the development of next-generation high-performance electronic devices.