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Impedance modeling of silica nanoparticle metal insulator metal capacitors

Abstract:

In this study, we have fabricated metal-insulator-metal (MIM) capacitors where the insulator layer is made of 255 nm diameter silica nanospheres. The MIM devices have been characterized and modeled by electrochemical impedance spectroscopy (EIS) and charge-discharge transients. Fitting the results with modified Randles models agreed well with three constant phase elements, three leakage resistors, and a Warburg element. According to the results of the fitting of the charge-discharge measurements and of the modified Randles model, values of real capacitances up to thousand times larger than the theoretical capacitance of a similar capacitor with a continuous layer dielectric are found. These unexpected high capacitances seemed to be related to the ability of the nanospheres to trap electric charges due to surface hydroxyl groups that are originated by the adsorption of water molecules, thereby indicating that the environmental humidity plays a role. This has been ascertained by measurements at several temperatures above the ambient and the resulting capacitance decreases as temperatures increases. Furthermore, active and reactive parts of the complex power have been measured showing capacitive or resistive behavior depending on the frequency. These results suggest that this novel MIM device based on nanospheres may be a new baseline technology for supercapacitor technology.