Towards High Energy Density 3D-integrated Lithium-ion Micro-batteries
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Towards High Energy Density 3D-integrated Lithium-ion Micro-batteries J.F.M. Oudenhoven1, L. Baggetto1, R.A.H. Niessen2, H.C.M. Knoops1,3, M.E. Donders1,3, T. van Dongen2, M.H.J.M. de Croon1, W.M.M. Kessels1 and P.H.L. Notten1,2 1
Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands Philips Research Eindhoven, High Tech Campus 4, 5656 AE Eindhoven, The Netherlands 3 Materials Innovation Institute M2i, P.O. Box 5008, 2600 GA Delft, The Netherlands 2
ABSTRACT To investigate the feasibility of a 3D integrated all-solid-state micro-battery, the deposition of several battery materials was investigated. Deposition techniques where used that are in principle able to deposit step conformally in 3D structures: ALD was used to create a conductive Pt current collector, and LPCVD was applied for the deposition of poly-silicon anodes and LiCoO2 cathodes. The layers, initially deposited on planar substrates, showed the expected physical and electrochemical behavior and are in principle suitable for solid state micro-batteries. INTRODUCTION Micro-electronic devices play an ever increasing role in our everyday life. Power supply and power storage form nowadays one of the major design constraints for these devices. Thin film micro-batteries can be employed to facilitate the size reduction of these devices, but their capacity is still relatively low. To enhance the power and charge capacity of these batteries, the volume of the substrate can be more efficiently utilized by depositing thin film batteries on 3D structured substrates yielding a higher charge and power capacity with the same footprint area (Figure 1) [1].
Cathode
Si-substrate
Solid Electrolyte Anode
Figure 1. Proposed 3D integrated micro-battery.
Barrier layer Current collector
A three dimensional substrate can be created in silicon using anisotropic reactive ion etching (RIE) [2]. This is a relatively mature technique that is frequently applied in silicon integrated device technology. By etching pores, trenches or pillars the surface area can be enhanced and the geometry can be optimized for mechanical stability or deposition requirements. To produce the active layers of 3D thin film batteries, various deposition approaches are proposed. Physical vapor deposition (PVD) has already been applied for planar battery materials [3] and will suffice for small aspect ratio structures as has been shown for electronic barrier layers [4]. When, however, a larger surface area enhancement is desired and higher aspect ratio structures are used, PVD techniques are unable to deposit films with sufficient step conformality. Therefore chemical vapor deposition (CVD) techniques and atomic layer deposition (ALD) are interesting alternatives. Although a few publications have been issued in which CVD was used for the deposition of a LiCoO2 battery cathode [5-7], the generally available documentation for the production of battery materials using ALD and CVD is very limited. Therefore the deposition of battery layers on planar structures ne
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