We have successfully fabricated a 3D super-capacitor, which can be integrated with MEMS in a wafer level, using Si trenches (aspect ratio = 53) and ultra-conformal supercritical fluid deposition (SCFD) of Cu/SiO2 layers. Taking advantage of large inner surface area of the trenches, the 3D capacitor exhibited 70 times larger capacitance than a planar one having the same projected area, and low leakage current density (<;3.8×10-5 A/cm2) at an electric field of 1.5-2.4 MV/cm. This achievement is brought about by ultra-conformal and void-free coating of a SiO2 layer, having a dielectric constant equivalent to the film by conventional deposition method, and ultra-conformal deposition of Cu on oxide surface, both of which are significant achievements for SCFD. Metal-insulator-metal structure is also feasible using a similar process technology, which will allow us monolithic integration of a power storage element, a power generator and sensors in a single MEMS chip for the purpose of battery-free sensor nodes in sensor network.
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