Electrical characteristics of double stacked Ppy-PVA supercapacitor for powering biomedical MEMS devices

Abstract

This paper discusses planar and double stacked supercapacitors with interwoven electrodes. Here, we study surface charge densities and capacitance performances of planar and sandwiched double stacked interdigital electrodes MEMS supercapacitors, and compare the improvement in electrical parameters between the two designs. The double stacked supercapacitor was constructed of polypyrrole (Ppy) coated nickel electrode as current collector and polyvinyl alcohol (PVA) as solid state electrolyte. Double stacked supercapacitor has the advantage of having increased charging capacity while maintaining equal layout area compared to the planar design. The extra charging capacity comes from the stacking of two mirrored planar supercapacitor via flip-chip processes. Another significant advantage of this technique is the completed supercapacitor cells are readily ‘flip chip’ packaged at wafer level, thus protecting the die from damage during back end processes. The planar and double stacked supercapacitor designs were simulated using Coventorware 2008 for capacitance performance analysis and COMSOL ver. 4.2 for electrical performance verification. It is observed that capacitance increases linearly with increasing number of cell, due to charge interactions among adjacent cells. In terms of electrical performance, maximum current response of 1.6 A/m was achieved. Double stacked supercapacitor has same layout, only slightly thicker compared to the planar structure due to double stacking, but with much superior charging capacity.