High Performance Micro-Supercapacitors Integrated on Both Silicon Chips and Flexible Polyimide Substrate
Authors: Brousse Kevin , Nguyen Son , Pinaud Sebastien , Lethien Christophe , Soulantica Katerina , Chaudret Bruno , Respaud Marc , Taberna Pierre-Louis , Simon Patrice 
Published: February 2020

Modern microelectronic systems, such as electronic papers, smart clothes, sensors or biomedical devices, demand new energy storage devices to achieve their tasks (1, 2). While batteries suffer from limited power capabilities and cyclability, owing to the faradic mechanisms involved during energy delivery and harvesting, electrochemical double layer supercapacitors (or so called EDLCs) can handle fast charge and discharge over 1,000,000 cycles (3). Indeed, EDLCs store energy via reversible adsorption of ions from an electrolyte at the surface of high-surface-area carbons, or by fast redox reactions occurring at the surface of metal oxide or polymer electrodes (4). However, standard electrode preparation, consisting in mixing the active material with a polymer binder, is not compatible with micro-fabrication processes. Therefore, high performance micro-supercapacitors have to be prepared using non wet processing routes. In this work, nanoporous carbide-derived carbon (CDC) films were integrated onto silicon chips by removing under chlorine atmosphere the metallic atoms of a thin film titanium carbide (TiC) precursor sputtered on silicon wafers (5). The TiC precursor could be patterned through reactive ion etching, thus leading to interdigitated on-chip CDC-based micro-supercapacitors after partial chlorination. The as-prepared devices provided capacitance values up to 410 F.cm-3 (205 mF.cm-2) in 1M H2SO4 with more than 50% of the initial capacitance preserved for 0.9 s discharge time (6). Full chlorination could lead, in certain conditions, to self-supported CDC films of several mm², which were transferred on PET. The flexible CDC electrode delivered 240 mF.cm-2 in sulfuric acid (6).
A second strategy consisted in the preparation of flexible micro-supercapacitors via laser-writing of commercial RuO2 on polyimide substrate. Indeed, laser-writing provides facile and scalable engineering with low cost (7), as less than 1 mg.cm-2 of active material are needed in micro-electrodes. Thus, RuO2 interdigitated electrodes were obtained from laser-writing of a precursor mixture of commercial RuO2.xH2O powder and HAuCl4.3H2O salt, spin-coated onto KaptonTM. Laser-writing led to current collector-free and mechanically stable flexible interdigitated RuO2 electrodes. Capacitance values of ~ 30 mF.cm-2 were recorded at 20 mV.s-1 in 1M H2SO4 for the flexible device. This work open the way for the design of high performance micro-devices at large scale.
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