On-Chip Integrated Solid-State Micro-Supercapacitor

Following the trend of electronic device miniaturization, on-chip integrated solid-state micro-supercapcaitors (MS) were fabricated based on vertically aligned carbon nanofibers (VACNFs) as electrode materials and polymeric gel electrolyte as the solid electrolyte. The VACNFs were grown at 390 °C and 550 °C temperature on interdigitated micro-patterns, where the dimensions of the digits were kept the same but the gap between the digits varied from 10-100 μm. A maximum capacitance of 1 mF/cm2 and 0.53mF/cm2 (combined footprint area of digits and gaps) were measured for devices with CNFs grown at 390 °C and 20 μm gap, for 550 °C and 10 μm gap, respectively. These capacitances are an order of magnitude higher than the one for solid dielectric based silicon trenches capacitors. The low temperature MS show an inverse capacitance relation with the gap size whereas high temperature shows random behavior. High characteristic frequencies at 45° phase angle are 114 Hz for 100 μm gap and 142 Hz 30 μm gap for 390 °C and 550 °C temperatures. A model for the interdigitated capacitors was developed and the results showed that by eliminating the current collector resistances the characteristic frequencies can be increased to 965 Hz and 866 Hz from 67 Hz and 127 Hz for 10 μm gap patterns for 390 °C and 550 °C temperatures. The entire fabrication was done using CMOS compatible processes thus enabling integration directly on active CMOS chip.