High-performance solid-state on-chip supercapacitors based on Si nanowires coated with ruthenium oxide via atomic layer deposition

Solid-state on-chip supercapacitors based on ruthenium oxide coated silicon nanowires were fabricated using a process that is compatible with silicon integrated circuit processing. Ordered arrays of silicon nanowires were fabricated using metal-assisted anodic etching (MME). Atomic layer deposition (ALD) was used to form a uniform coating of ruthenium oxide on high-aspect-ratio silicon nanowires at a moderate temperature of 290 degrees C. Coated nanowire electrodes were studied using cyclic voltammetry and charge-discharge tests in a neutral Na2SO4 electrolyte, and a specific capacitance of 19 mFcm(-2) was achieved at 5 mVs(-1). Solid state nanowire capacitors were then fabricated with symmetric face to face nanowire arrays separated by a polymer-based electrolyte. This device exhibited a specific capacitance as high as 6.5 mFcm(-2) at 2 mVs(-1). The full device was tested over 10000 cycles under galvanostatic charge discharge at 0.4 mAcm(-2), and showed a retention of 92% of the specific capacitance. The specific capacitance was found to scale with the total nanowire surface area, as controlled by controlling the aspect ratios of the wires. The solid state nanowire-based device also achieved high specific energies without sacrificing power performance. (C) 2016 Elsevier B.V. All rights reserved.