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Cheng Chi1 Dezhao LI1 Baoling Huang1

1, The Hong Kong University of Science and Technology, Hong Kong, , Hong Kong

High-performance on-chip micro-supercapacitors (MSCs) provide a promising solution to integrated energy storage for portable and wearable electronics. For on-chip integration, it is required that the adopted materials and fabrication techniques for MSCs should be fully compatible with standard IC fabrication process. Meanwhile, wafer scale fabrication of high performance on-chip MSCs remains a great challenge. In this work, we report a promising all-solid-state on-chip MSCs using IC-compatible 3D Ni/Si nano-forest electrodes fabricated using standard microfabrication process together with (PVDF-HFP)/LiBOB/TiO2 solid polymer electrolyte. The MSC electrodes were interdigital structures comprising of nickel-coated n-type silicon beams with monolithically integrated silicon nanowire forest. Unlike many previous studies adopting liquid or gel electrolytes, we developed an all-solid-state polymer electrolyte PVDF-HFP/LiBOB/TiO2 with a high ionic conductivity up to 10-4 S cm-1 to address the compatibility, leakage and encapsulation issues caused by liquid or gel electrolytes. The developed interdigital all-solid-state on-chip MSCs exhibited a highly stable double layer capacitive behavior with a high areal capacitance of 900 μF cm-2 at a scan rate of 20 mV s-1. The devices also demonstrated excellent cyclic stability, over 95% capacitance retention after 10000 cycles at a scan rate of 200 mV s-1. Furthermore, the fabricated on-chip solid-state MSCs showed a high integration density with a minimum interspace below 3 μm and foot-print area less than 0.3 mm2. It is expected that this solid-state 3D silicon nano-forest based on-chip device could be useful in many applications requiring on-chip energy storage.

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