• Grigoras, Kestutis
• Yli-Rantala, Elina
• Ahopelto, Jouni
• Keskinen, Jari
• Prunnila, Mika
• Välimäki, Hannu
• Gronberg, Leif
• Laakso, Sampo
• Kauranen, Pertti

Abstract

Today's supercapacitor energy storages are typicallydiscrete devices aimed for printed boards and powerapplications. The development of autonomous sensornetworks and wearable electronics and the miniaturizationof mobile devices would benefit substantially fromsolutions in which the energy storage is integrated withthe active device. Nanostructures based on porous silicon(PS) provide a route towards integration due to the veryhigh inherent surface area to volume ratio andcompatibility with microelectronics fabricationprocesses. Unfortunately, pristine PS has limitedwettability and poor chemical stability in electrolytesand the high resistance of the PS matrix severely limitsthe power efficiency. In this work, we demonstrate thatexcellent wettability and electro-chemical properties inaqueous and organic electrolytes can be obtained bycoating the PS matrix with an ultra-thin layer oftitanium nitride by atomic layer deposition. Our approachleads to very high specific capacitance (15 F cm-3),energy density (1.3 mWh cm-3), power density (up to 214 Wcm-3) and excellent stability (more than 13,000 cycles).Furthermore, we show that the PS-TiN nanomaterial can beintegrated inside a silicon chip monolithically bycombining MEMS and nanofabrication techniques. This leadsto realization of in-chip supercapacitor, i.e., it opensa new way to exploit the otherwise inactive volume of asilicon chip to store energy.

Topics

• porous
• density
• impedance spectroscopy
• surface
• energy density
• nitride
• chemical stability
• Silicon
• titanium
• tin
• atomic layer deposition