(Invited) Wafer Level Fabrication Process of High Performance Micro-Supercapacitors (2016)

Nowadays, miniaturized power sources are key devices for providing autonomy to smart and connected sensors. To reach this goal, the current trend is to fabricate micro-storage unit such as microbatteries (MB) or microsupercapacitors (MSC) at the wafer level. According to the limited surface of such device, the metrics should be reported as normalized to the footprint area (mF, µWh and mW per cm 2 ). With such metrics, the average energy density of most of MSC 1,2 (Onions like carbon, graphene) is found to be close to 1 µWh/cm 2 which is not enough to get autonomous miniaturized and connected sensors. Within this study, two different approaches will be reported to significantly improve the performances of MSC. One attractive way to improve the areal energy density of MSC is to enhance the material mass loading while keeping low the footprint area. To meet this requirement 3 , on chip fabrication of 3D MSC is proposed. Wafer level fabrication process on high area enlargement factor 3D scaffold (AEF # 50) is achieved. Step conformal deposition of MnO 2 thin film (electrophoretic deposition) on this 3D template is performed and the MSC are tested either in aqueous electrolyte (0.5M Na 2 SO 4 ) or in EMI-TFSI aprotic ionic liquids (AILs). The areal energy density of the proposed micro-device is close to 10 µWh/cm 2 while maintaining high areal power density of 10 mW/cm 2 . Carbon derived carbide (CDC) based MSC is the second followed way to propose on chip high performance device. The fine-tuned chlorination of TiC thin films deposited and patterned as interdigitated planar electrodes is performed in the framework of this study 4 . CDC based MSC were directly fabricated on silicon wafer. The corresponding areal energy density is around 1 µWh/cm 2 for aqueous based device (1M H 2 SO 4 ) and higher than 20 µWh/cm 2 for MSC tested in organic electrolyte (2M EMI-BF 4 in ACN). The power density is measured to be close to 100 mW/cm 2 . Finally, MSC based on vanadium nitride 5 thin films grown either by sputtering technique (for planar MSC) or by atomic layer deposition technology (for 3D MSC) will be reported. The objective of these studies is to clearly find the suitable technology allowing to propose the fabrication of high areal energy density, small footprint area MSC and to move toward solid state configuration. References 1. El-Kady, M. F. &amp; Kaner, R. B. Scalable fabrication of high-power graphene micro-supercapacitors for flexible and on-chip energy storage. Nat. Commun. 4, 1475 (2013). 2. Pech, D. et al. Ultrahigh-power micrometre-sized supercapacitors based on onion-like carbon. Nat. Nanotechnol. 5, 651–654 (2010). 3. Eustache, E., Douard, C., Retoux, R., Lethien, C. &amp; Brousse, T. MnO 2 Thin Films on 3D Scaffold: Microsupercapacitor Electrodes Competing with ‘bulk’ Carbon Electrodes. Adv. Energy Mater. 5, 1–8 (2015). 4. Huang, P. et al. On-chip and freestanding elastic carbon films for micro-supercapacitors. Science. 351, 691–695 (2016). 5. Lucio-Porto, R. et al. VN thin films as electrode materials for electrochemical capacitors. Electrochim. Acta 141, 203–211 (2014). Acknowledgments: The authors want to thank the French network of the electrochemical energy storage (RS2E) for this support. The French RENATECH network is greatly acknowledged.