OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 16766To link to this article :

The fabrication of miniaturized electrochemical energy storage systems is essential for the development of future electronic devices for Internet of Thing applications. This paper aims at reviewing the current micro-supercapacitor technologies and at defining the guidelines to produce high performance micro-devices with special focuses onto the 3D designs as well as the fabrication of solid state miniaturized devices to solve the packaging issue.

Nowadays, millimeter scale power sources are key devices for providing autonomy to smart, connected and miniaturized sensors. However, until now, planar solid state microbatteries do not yet exhibit a sufficient surface energy density. In that context, architectured 3D (3 dimensional) microbatteries appear therefore to be a good solution to improve the material mass loading while keeping small the footprint area. Beside the design itself of the 3D microbaterry, one important technological barrier to address is the conformal deposition of thin films (lithiated or not) on 3D structures. For that purpose, Atomic Layer Deposition (ALD) technology is a powerful technique that enable conformal coatings of thin film on complex substrate. In this paper, an original, robust and highly efficient 3D scaffold is proposed to significantly improve the geometrical surface of miniaturized 3D microbattery.Four functional layers composing the 3D lithium ion microbattery stacking has been Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))

Unveiling the charge storage mechanism of vanadium nitride to defy the limits of on-chip micro-supercapacitors.

International audienc

Smart integrated miniaturized microsystems require harvesting and storage power sources in order to be autonomous. From the energy point of view, commercially available lithium-ion microbatteries with planar topology do not have suffi cient performance to address the challenging autonomy of microsystems. In aiming for this goal, new concepts based on 3D topologies have been published [ 1 ] in last ten years. By developing a 3D topology, the surface area, and thus the capacity, of the device is increased. The fabrication of high-surfacecapacity devices at the microscale is performed by 1) nano-/micro-structuring a substrate and 2) making a conformal deposition of an electrochemically active thin fi lm on the 3D topology. To achieve conformal deposition on steps and other 3D features, electrodeposition (ED) or highvacuum atomic layer deposition (ALD) are required. The gain obtained with the 3D topology is referred to as the ratio between the 3D and 2D surface areas, and it is known as the area enlargement factor (AEF). The energy density is drastically increased in the 3D topology compared to the planar topology. The power density is also enhanced because the thickness of the 3D deposited material is kept relatively low; the diffusion length of the lithium ions inside the electrode material is reduced, leading to an increase in the charge/discharge rate of the 3D microstorage device.Interdigitated 3D lithium-ion microbatteries based on carbon micro-electromechanical system (C-MEMS) technology with a surface capacity close to 125 µA h cm -2 have been reported [ 2,3 ] by Dunn and co-workers. The micromachining of silicon or glass substrates has been performed by the Peled group [ 4,5 ] in order to fabricate a liquid-based 3D lithium-ion microbattery. Microcontainers fi lled with the battery materials have reached 1 mA h cm -2 under 2 V; the exacerbated surface capacity is clearly enhanced due to the 3D topology. Recently, an interdigitated lithium-ion microbattery based on porous electrodes has been reported with power and energy capabilities greatly enhanced by the 3D porous network. [ 6 ] Simon and co-workers [ 7 ] have developed a nano-architectured aluminum-based 3D metallic current-collector; on top of the 3D nanostructure, a thin layer of anatase TiO 2 polymorph was deposited by ALD. An AEF of 10 is exhibited between the measured 2D and 3D surface capacity. An interesting concept using top-down and bottom-up approaches has been published by Gerasopoulos et al. [ 8 ] using low-aspectratio gold micropillars decorated with biological nano-objects (tobacco mosaic virus, TMV); an enhancement of the surface capacity of a V 2 O 5 thin fi lm deposited by ALD was demonstrated using this novel structure. Previously, Gerasopoulos [ 9 ] et al. reported the ALD of TiO 2 onto biological scaffolds composed of TMV. The TMV nanostructures had been covered beforehand by a nickel conductive layer. The bio-templating approach [ 10 ] has also been used by Kim et al. to fabricate a TiO 2 3D nanonetwork based on peptide assembly; a h...

The development of high voltage spinel LiMn 1.5 Ni 0.5 O 4 (LMNO) sputtered thin films on functional current collector was reported within the framework of this study. We have first solved the technological issue due to the PtSi phase which originates from the interdiffusion between silicon wafer and chromium/platinum current collector to form PtSi phase under annealing treatment. By substituting the Cr layer with a very dense and pinhole free Al 2 O 3 thin film deposited by ALD acting as a barrier diffusion between the silicon substrate and the LMNO layer, the synthesis process (sputtered thin films annealed under air at 700°C) has been validated. In the second part of this study, the behavior of the sputtered LMNO thin films as a function of the deposition pressure and the film thickness has been investigated. The deposition pressure has been found to play a key role on the Mn−Ni cations ordering in spinel-like structures (P4 3 32 ordered vs Fd3̅ m disordered spinel) and consequently on the electrochemical performance. We have thus shown that LMNO thin films deposited at 10 −2 mbar and annealed at 700°C deliver a normalized capacity of 65 μAh•cm −2 •μm −1 with good capacity retention upon cycling thanks to its disordered spinel structure. Moreover, the Coulombic efficiency has been shown to be highly dependent on the film thickness for high voltage LMNO thin film electrodes. To the best of the authors' knowledge, this work is one of the most complete study combining structural and electrochemical characterizations of the LMNO thin film obtained by sputtering deposition on Si/Al 2 O 3 /Pt functional current collectors.

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