Step-conformal deposition of TiO2 and MnO2 electrodes on advanced silicon microstructures for 3D Li-ion microbatteries and micro-supercapacitors
Résumé
To get autonomous smart microsystem, a miniaturized power source should be integrated. As the device is surface limited, the energy and power performances of commercially available planar microbatteries and micro-supercapacitors are not sufficient to reach this goal. To improve their performances while keeping constant the footprint area of such devices, a 3D topology is proposed. The silicon micropillars and microtubes fabricated by a top down approach allows to reach a high area enlargement factor (AEF). Energy density can be increased by one or two orders of magnitude compared to standard planar micro-devices, thus providing improved autonomy to the powered microsytems. Step conformal deposition of platinum (current collector) and TiO2 (negative electrode of the Li-ion microbattery) are performed on the 3D structures by Atomic Layer Deposition facility. With a 3D scaffold having an AEF close to 25 combined with a 150 nm thick TiO2, a surface capacity of 0.2 mAh/cm2 at C/10 is reported. A micro-supercapacitor electrode based on a thin manganese dioxide film is conformably grown by pulsed electrodeposition on the 3D topologies. A MnO2 film (275 nm thick) reaches 250 mF/cm? at 5 mV/s. The surface capacitance is drastically enhanced compared to a standard 2D electrode with a comparable thickness. This study shows promising AEF leading to high energy density while keeping enough spacing in the microstuctrures array to allow the deposition of the overlying layers.
