Macroporous silicon for high-capacitance devices using metal electrodes.

Didac Vega,Jordi Reina,Ángel Rodríguez,Ferran Martí,Ramón Pavón

doi:10.1186/1556-276x-9-473

Didac Vega, Jordi Reina + Show 3 more

Open Access

https://doi.org/10.1186/1556-276x-9-473

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Abstract

In this paper, high-capacity energy storage devices based on macroporous silicon are demonstrated. Small footprint devices with large specific capacitances up to 100 nF/mm2, and an absolute capacitance above 15 μF, have been successfully fabricated using standard microelectronics and MEMS techniques. The fabricated devices are suitable for high-density system integration. The use of 3-D silicon structures allows achieving a large surface to volume ratio. The macroporous silicon structures are fabricated by electrochemical etching of silicon. This technique allows creating large structures of tubes with either straight or modulated radial profiles in depth. Furthermore, a very large aspect ratio is possible with this fabrication method. Macroporous silicon grown this way permits well-controlled structure definition with excellent repeatability and surface quality. Additionally, structure geometry can be accurately controlled to meet designer specifications. Macroporous silicon is used as one of the electrodes over which a silicon dioxide insulating layer is grown. Several insulator thicknesses have been tested. The second capacitor electrode is a solid nickel filling of the pores prepared by electroplating in a low-temperature industry standard process. The use of high-conductivity materials allows reaching small equivalent series resistance near 1 Ω. Thanks to these improvements, the presented devices are capable of operating up to 10 kHz.PACS84.32.Tt; 81.15.Pq; 81.05.Rm

Highlights

The fast-growing portable and embedded device market has imposed increasing concerns in energy storage
Several macroporous silicon membranes were prepared using the EE technique for the pore fabrication and local KOH etching for the membrane opening
Macroporous silicon fabricated using the EE technique has good geometry uniformity and is very repeatable. This has been confirmed with scanning electron microscopy (SEM) analysis of some samples, resulting in pore diameters within a few nanometres and lengths about a few microns off of the desired values

Summary

Introduction

The fast-growing portable and embedded device market has imposed increasing concerns in energy storage. After taking into account the devices’ interfaces to the outer world, the designer faces severe constraints to fit energy storage elements such as batteries, inductors and capacitors and meet the desired weight, size, shape and performance goals for the intended application. This is especially important for the consumer market, which demands highperformance computing for long operating periods but keeping size and weight to a minimum. Primary energy sources have usually been batteries [1].

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