基于3D体硅技术的高性能碳基微型电容器研究

Co-planar micro-supercapacitor (MSC), as a kind of newly developed energy storage devices, has attracted increasing interests owing to its ultrahigh power density and high level of integration with other on-chip devices. Plenty of research has been conducted to improve electrochemical performances of MSCs and maximum power density of more than 1000 W/cm3 was achieved. However, the interface area between electrode and electrolyte is limited to the upper surface of the substrate, only occupying a small part of its total volume. Therefore, energy densities and specific capacitances of MSCs do not present superior advantages when compared with traditional sandwich structured supercapacitors. To optimize the electrochemical performance of MSCs, a 3-dimensional (3D) bulk-silicon electrode design is proposed. In aim to improve space utilization ratio of substrate, the silicon wafer is etching through for forming the 3D bulk silicon electrodes. In this way, contact interface areas between electrodes and electrolytes are obviously increased and it is expected that energy densities and specific capacitances of MSCs can be enhanced. In addition, low-density vertical-aligned carbon nanotube (VACNT) array is synthesized onto the surface of 3D electrodes, acting as a nanostructured matrix. The VACNT array is expected to effectively improve conductivity of 3D bulk silicon electrodes due to its straight physical morphology and outstanding electrical property. Moreover, this VACNT array has a low-density arrangement and uniform interspacing which could offers a promising structural support for further deposition of advanced material with higher specific capacitance. Through these approaches, it is expected that the energy density can be improved from 10 mWh/cm3 of common planar MSCs to 50 mWh/cm3 of 3D bulk-silicon electrodes based MSCs.

平面微型电容器作为一种新型储能器件，凭借极高的功率密度和与良好的集成性引起了广泛的关注。近年来，对平面电容器性能的研究取得了显著的进展，电极的功率密度最高可以超过1000W/cm3。然而，相对于器件整体尺寸而言，由于衬底占较大比重，电极与电解液的接触面积只在衬底上表面的特定区域，导致整个器件的有效利用面积十分有限。相比于传统三明治结构的电容器来说，平面微型电容器的能量密度并不显著，大多在10mWh/cm3这个范围内。本项目提出了一种对硅基衬底进行整片刻蚀来制造体硅3D结构微型电容器的设计。依靠对衬底纵向空间的完全利用，极大地提升电极与电解液的有效接触面积。此外，通过在体硅3D电极上生长低密度的垂直碳纳米管阵列，一方面改善3D体硅电极的导电性，另一方面为进一步沉积具有高比电容密度的活性材料提供良好的纳米结构基底。预期将微型电容器的能量密度提升到50mWh/cm3以上。

平面电容器作为一种新型储能器件，并凭借高功率密度以及良好的集成度引起了广泛的研究，并有望成为小型化电子器件发展的基石。然而，在实际应用中，由于衬底不充分利用导致整个器件的有效利用面积十分有限，进而造成平面微型电容器的能量密度并不显著。本项目采用深硅刻蚀工艺（DRIE）制备3D体硅电极结构，在保证器件尺寸不变的情况下，利用电极的纵向维度来增加电极与电解液的有效接触面积和活性材料负载。并通过活性材料的包覆，改善电极的导电性和粗糙度，增加电容器件的比电容和能量密度。基于3D梳齿电极结构，Si/C/MnO2电容器件达到了2.62 μWh cm-2的能量密度和117.82 μW cm-2的功率密度。高导电性、高深宽比结构的3D Si/C/CNT@TiC电容器展示了8倍的电容提升，并在10000次充放电测试后，仍保持98%以上的电化学性能。这源于高长径比的CNT结构引入的高导电路径和大比表面积。为了进一步利用3D梳齿的结构优势，我们利用DIRE进行3D硅基多孔叉指电极的制备。与非多孔电极相比，多孔电极的离子扩散电阻减少了43%，结构表面积增大了50%。最终，将3D多孔微电容器的比电容提升0.3-1.3倍。此外，通过将电容器件集成到芯片上，不仅可以作为滤波器，实现纹波系数为1.5%的稳定电压输出。而且可以实现紫外监控，通过微纳制造的自供电电容器件驱动白光LED达60 s以上。这些结果不仅展示出基于3D体硅技术的微型电容器在能量存储方面的巨大潜力，还显示出MSC和芯片集成的广泛应用前景。

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