Packaged Flexible Planar Copper Foil Fractional-Order ‘0.61–0.87’ Capacitors: Series/Parallel Combinations

Abstract

The fabrication of packaged, flexible, and planar fractional-order capacitors (FOCs) using copper foil electrodes and thin films of PVDF polymer nanocomposite dielectric is presented in this paper. An extensive comparison of FOC properties is made by using two separate conductive fillers, i.e., graphene nanosheets (GNS) and reduced graphene oxide (rGO). Similar fractional-order is observed at a particular filler loading in both types of FOCs; however, differences in the pseudocapacitance values and width of the constant phase (CP) zone exists. Fractional order α (alpha) is reported to vary in the range 0.61–0.87 in impedance measurements made on individual samples of rGO/PVDF and GNS/PVDF FOCs and series/parallel connections of two identical-order FOCs. For series/parallel connection of arbitrary-order FOCs, α varies from 0.61 to 0.83. Phase angle variation ranges from − 56.2° to − 79° for standalone pure FOC samples, whereas, for series/parallel connection of identical or arbitrary order FOCs, phase ranges from − 54.94° to − 77.75°. Phase ripple varies between ± 1.1° and ± 4.8°, and a maximum CP zone of 4 decades (1 kHz to 10 MHz) for the fabricated samples is reported. Industrial manufacturing of large-value capacitors demands materials to be flexible to enable rolling of large-area electrodes into a miniature device. FOCs fabricated in this work match the design specifications of commercial standard thin film capacitors and show high-value capacitances as well as flexibility of materials and structure.