Highly N-doped Silicon Nanowires as a Possible Alternative to Carbon for On-chip Electrochemical Capacitors

Abstract

Highly n-doped silicon nanowires (SiNWs) have been grown by a chemical vapor deposition process and have been investigated as possible electrodes for electrochemical capacitors (ECs) micro-devices. Their performances have been compared to existing literature on the field, which shows the use of SiNWs fabricated via different techniques, SiC coated SiNWs and porous silicon layers. The double layer capacitance of n-doped silicon wafer is ≈6 µF cm⁻² in standard organic electrolyte, and this value can be increased by nanostructuration of SiNWs up to 440 µF cm⁻² by tuning deposition parameters. Similar values are found in the literature. Symmetrical microdevices based on two identical SiNWs electrodes can be operated in organic based electrolytes within a 1.2 V voltage window. The devices show excellent cycling efficiency over more than 2000 cycles, with capacitance value of 51 µF cm⁻² and an energy density of 10 nWh cm⁻² (37 µJ cm⁻²). The increase of specific surface area by different techniques may drastically boost these values in the near future.