一般而言，平行板電容器是由兩導體作為電極板，並將兩電極隔開一距離所形成的結構，因此，增加電容值最直接的方法即為增加電極之表面積。為了增加電極之表面積，本實驗利用兩平行互繞之阿基米德螺線作為平行板電容之設計，以達到在固定區域內具有最大長度之電極。於電極材料選擇上，利用垂直配向之多壁奈米碳管良好導電性、化學穩定性佳及高數密度等特點，並結合二氧化鈦奈米結構，利用其高介電係數之特性使電容值獲得提升。本實驗之奈米碳管使用熱化學氣相沉積法成長於Eagle 2000玻璃基板上，隨後利用有機金屬化學氣相沉積法將二氧化鈦奈米結構直接披覆於奈米碳管表面。本研究以不同奈米碳管之高度為參數，分別對單純奈米碳管及披覆二氧化鈦後之元件進行阻抗成份之特性分析。研究結果顯示，電容值會隨著奈米碳管高度的增加而增加，且經二氧化鈦奈米結構披覆過後電容值亦獲得提升。而其電容之量測值較理論值為小，其原因除了兩電極之間距過大而造成電容之體積效能較差之外，電極間之電場不均勻分佈，進而造成電荷密度降低，導致電容值下降。整體而言，此阿基米德螺線形奈米碳管電容結構之設計，可經由填入不同介電質而改變其電容值，以提供不同應用之可能。

In general, a parallel capacitor consists of two conductive plates which are separated by a distance. Therefore, the direct method to enhance the capacitance is to increase the surface area of electrodes. In this research, two Archimedean spirals were designed as the pattern of the capacitor electrodes that can utilize the surface area effectively. For electrode material, vertically aligned carbon nanotubes (VACNTs) were considered as a good option due to its properties such as good conductivity, chemical stability and high number density. Besides, titanium dioxide (TiO2) nanostructures coated onto carbon nanotubes (CNTs) were used to improve the capacitance because of the high dielectric constant of TiO2. In this study, the patterned VACNTs were grown on the Eagle 2000 substrate by thermal chemical vapor deposition method, and then the TiO2 nanostructure was coated on the surface of the CNTs using metal organic chemical deposition method. In addition, the impedance characteristics of different capacitor devices were analyzed individually. The TiO2 coverage layer could actually enhance the capacitance. The practical capacitance values were lower than those theoretical values because the distance between the electrodes is too large which leads to a poor volume efficiency. Moreover, the non-uniform electric field distribution between two electrodes causes the lower charge density and the decreasing of capacitance. In conclusion, this CNT-based capacitor structure can provide an approach to insert various dielectric materials to change the capacitance, and can apply to different applications.

[1] M. Milanovic, G. Stojanovic, L. M. Nikolic, M. Radovanovic, B. Skoric, and A. Miletic, "Electrical and structural characterisation of nanostructured titania coatings deposited on interdigitated electrode system," Mater. Chem. Phys., vol. 130, pp. 769-774, 2011.
[2] M. Kitsara, D. Goustouridis, S. Chatzandroulis, M. Chatzichristidi, I. Raptis, T. Ganetsos, R. Igreja, and C. J. Dias, "Single chip interdigitated electrode capacitive chemical sensor arrays," Sensor Actuat. B-Chem., vol. 127, pp. 186-192, 2007.
[3] S. Iijima, “Helical microtubules of graphitic carbon,” Nature, vol. 354, pp. 56-58, 1991.
[4] S. Wijewardane, "Potential applicability of CNT and CNT/composites to implement ASEC concept: A review article," Sol. Energy, vol. 83, pp. 1379-1389, 2009.
[5] M. B. Jakubinek, M. B. Johnson, M. A. White, C. Jayasinghe, G. Li, W. Cho, M. J. Schulz, and V. Shanov, "Thermal and electrical conductivity of array-spun multi-walled carbon nanotube yarns," Carbon, vol. 50, pp. 244-248, 2012.
[6] E. Dervishi, Z. Li, Y. Xu, V. Saini, A. R. Biris, D. Lupu, and A. S. Biris, "Carbon nanotubes: Synthesis, properties, and applications," Particul. Sci. Technol., vol. 27, pp. 107-125, 2009.
[7] A. Cao, H. Zhu, X. Zhang, X. Li, D. Ruan, C. Xu, B. Wei, J. Liang, and D. Wu, "Hydrogen storage of dense-aligned carbon nanotubes," Chem. Phys. Lett., vol. 342, pp. 510-514, 2001.
[8] H. Ko and V. V. Tsukruk, "Liquid-Crystalline Processing of Highly Oriented Carbon Nanotube Arrays for Thin-Film Transistors," Nano Lett., vol. 6, pp. 1443-1448, 2006.
[9] Y. M. Chen, J. H. Cai, Y. S. Huang, K. Y. Lee, and D. S. Tsai, "Preparation and characterization of iridium dioxide-carbon nanotube nanocomposites for supercapacitors," Nanotechnology, vol. 22, pp. 115706-1-115706-7, 2011.
[10] R. Bhatia, V. Prasad, and R. Menon, "Probing the inter-tube transport in aligned and random multiwall carbon nanotubes," J. Appl. Phys., vol. 109, pp. 053713-1-053713-5, 2011.
[11] T. Ikuno, H. Furuta, T. Yamamoto, S. Takahashi, M. Kamizono, S. I. Honda, M. Katayama, T. Hirao, and K. Oura, "Structural characterization of randomly and vertically oriented carbon nanotube films grown by chemical vapour deposition," Surf. Interface Anal., vol. 35, pp. 15-18, 2003.
[12] W. Li, C. Liang, J. Qiu, W. Zhou, H. Han, Z. Wei, G. Sun, and Q. Xin, "Carbon nanotubes as support for cathode catalyst of a direct methanol fuel cell," Carbon, vol. 40, pp. 791-794, 2002.
[13] C. Chen, W. Chen, and Y. Zhang, "Synthesis of carbon nano-tubes by pulsed laser ablation at normal pressure in metal nano-sol," Physica E., vol. 28, pp. 121-127, 2005.
[14] C.-M. Chen, Y.-M. Dai, J. G. Huang, and J.-M. Jehng, "Intermetallic catalyst for carbon nanotubes (CNTs) growth by thermal chemical vapor deposition method," Carbon, vol. 44, pp. 1808-1820, 2006.
[15] T. Dikonimos Makris, L. Giorgi, R. Giorgi, N. Lisi, and E. Salernitano, "CNT growth on alumina supported nickel catalyst by thermal CVD," Diam. Relat. Mater., vol. 14, pp. 815-819, 2005.
[16] C. Li, E. T. Thostenson, and T.-W. Chou, "Sensors and actuators based on carbon nanotubes and their composites: A review," Compos. Sci. Technol., vol. 68, pp. 1227-1249, 2008.
[17] R. Shah, X. Zhang, and S. Talapatra, "Electrochemical double layer capacitor electrodes using aligned carbon nanotubes grown directly on metals," Nanotechnology, vol. 20, pp. 395202-1-395202-5, 2009.
[18] C. Liu, K. S. Kim, J. Baek, Y. Cho, S. Han, S. W. Kim, N. K. Min, Y. Choi, J. U. Kim, and C. J. Lee, "Improved field emission properties of double-walled carbon nanotubes decorated with Ru nanoparticles," Carbon, vol. 47, pp. 1158-1164, 2009.
[19] D. V. Bavykin, J. M. Friedrich, and F. C. Walsh, "Protonated titanates and TiO2 nanostructured materials: Synthesis, properties, and applications," Adv. Mater., vol. 18, pp. 2807-2824, 2006.
[20] M. K. Bera, C. Mahata, and C. K. Maiti, "Reliability of ultra-thin titanium dioxide (TiO2) films on strained-Si," Thin Solid Films, vol. 517, pp. 27-30, 2008.
[21] S. K. Kim, W. D. Kim, K. M. Kim, C. S. Hwang, and J. Jeong, "High dielectric constant TiO2 thin films on a Ru electrode grown at 250°C by atomic-layer deposition," Appl. Phys. Lett., vol. 85, pp. 4112-4114, 2004.
[22] B. Hudec, K. Hu?ekova, A. Tarre, J. H. Han, S. Han, A. Rosova, W. Lee, A. Kasikov, S. J. Song, J. Aarik, C. S. Hwang, and K. Frohlich, "Electrical properties of TiO2-based MIM capacitors deposited by TiCl4 and TTIP based atomic layer deposition processes," Microelectron. Eng., vol. 88, pp. 1514-1516, 2011.
[23] K. Prasad, D. V. Pinjari, A. B. Pandit, and S. T. Mhaske, "Phase transformation of nanostructured titanium dioxide from anatase-to-rutile via combined ultrasound assisted sol–gel technique," Ultrason. Sonochem., vol. 17, pp. 409-415, 2010.
[24] Y. Djaoued, S. Badilescu, P. V. Ashrit, D. Bersani, P. P. Lottici, and J. Robichaud, "Study of anatase to rutile phase transition in nanocrystalline titania films," J. Sol-gel Sci. Techn., vol. 24, pp. 255-264, 2002.
[25] F. Alvarez-Ramirez and Y. Ruiz-Morales, "Ab Initio Molecular Dynamics Calculations of the Phase Transformation Mechanism for the Formation of TiO2 Titanate-Type Nanosheets from Anatase," Chem. Mater., vol. 19, pp. 2947-2959, 2007.
[26] Y. Hu, H. L. Tsai, and C. L. Huang, "Effect of brookite phase on the anatase-rutile transition in titania nanoparticles," J. Eur. Ceram. Soc., vol. 23, pp. 691-696, 2003.
[27] L. Moreno-Hagelsieb, B. Foultier, G. Laurent, R. Pampin, J. Remacle, J. P. Raskin, and D. Flandre, "Electrical detection of DNA hybridization: Three extraction techniques based on interdigitated Al/Al2O3 capacitors," Biosens. Bioelectron., vol. 22, pp. 2199-2207, 2007.
[28] J. K. Luo, M. Lin, Y. Q. Fu, L. Wang, A. J. Flewitt, S. M. Spearing, N. A. Fleck, and W. I. Milne, "MEMS based digital variable capacitors with a high-k dielectric insulator," Sensor actuat. A-Phys., vol. 132, pp. 139-146, 2006.
[29] M. Hosseini, G. Zhu, and Y. A. Peter, "A new formulation of fringing capacitance and its application to the control of parallel-plate electrostatic micro actuators," Analog. Integr. Circ. S., vol. 53, pp. 119-128, 2007.
[30] A. Bansal, B. C. Paul, and K. Roy, "Modeling and optimization of fringe capacitance of nanoscale DGMOS devices," IEEE T. Electron. Dev., vol. 52, pp. 256-262, 2005.
[31] W. Li, H. Zhang, C. Wang, Y. Zhang, L. Xu, K. Zhu, and S. Xie, "Raman characterization of aligned carbon nanotubes produced by thermal decomposition of hydrocarbon vapor," Appl. Phys. Lett., vol. 70, pp. 2684-2686, 1997.
[32] Q. Wu, L. Yu, Y. Ma, Y. Liao, R. Fang, L. Zhang, X. Chen, and K. Wang, "Raman investigation of amorphous carbon in diamond film treated by laser," J. Appl. Phys., vol. 93, pp. 94-100, 2003.
[33] M. S. Dresselhaus, G. Dresselhaus, R. Saito, and A. Jorio, "Raman spectroscopy of carbon nanotubes," Phys. Rep., vol. 409, pp. 47-99, 2005.
[34] L. M. Malard, M. A. Pimenta, G. Dresselhaus, and M. S. Dresselhaus, “Raman spectroscopy in graphene,” Phys. Rep., vol. 473, pp. 51-87, 2009.
[35] C. A. Chen, K. Y. Chen, Y. S. Huang, D. S. Tsai, K. K. Tiong, and F. Z. Chien, "X-ray diffraction and Raman scattering study of thermal-induced phase transformation in vertically aligned TiO2 nanocrystals grown on sapphire (100) via metal organic vapor deposition," J. Cryst. Growth, vol. 310, pp. 3663-3667, 2008.
[36] M. J. ??epanovi?, M. Gruji?-Broj?in, Z. D. Doh?evi?-Mitrovi?, and Z. V. Popovi?, "Characterization of anatase TiO2 nanopowder by variable-temperature Raman spectroscopy," Sci. Sinter., vol. 41, pp. 67-73, 2009.
[37] J. Y. Kim, H. S. Jung, J. H. No, J. R. Kim, and K. S. Hong, "Influence of anatase-rutile phase transformation on dielectric properties of sol-gel derived TiO2 thin films," J. Electroceram., vol. 16, pp. 447-451, 2006.
[38] J. W. Kim, P. Pasupathy, S. Zhang, and D. P. Neikirk, "Measurement of liquid complex dielectric constants using non-contact sensors," Sensors, 2009 IEEE, 2009, pp. 2017-2020.
[39] W. Laureyn, D. Nelis, P. Van Gerwen, K. Baert, L. Hermans, R. Magnee, J. J. Pireaux, and G. Maes, "Nanoscaled interdigitated titanium electrodes for impedimetric biosensing," Sensor Actuat. B-Chem., vol. 68, pp. 360-370, 2000.
[40] R. S. Chen, C. A. Chen, W. C. Wang, H. Y. Tsai, and Y. S. Huang, "Transport properties in single-crystalline rutile TiO2 nanorods," Appl. Phys. Lett., vol. 99, 2011.
[41] Y.-R. Huang, J.-R. Huang, Y.-M. Chen, Y.-S. Huang, G. Keiser, S.-L. Lee, and K.-Y. Lee, "Design and fabrication of a carbon-nanotube-based capacitor patterned on an Archimedean spiral," Solid State Commun., vol. 151, pp. 1022-1024, 2011.
[42] S. O. Kasap, "Principles of electronic materials and devices," 3rd ed., McGraw-Hill, New York, 2006.
[43] N. H. Langton and E. E. Gunn, "The electric field of a dielectric heating work circuit," J. Br. Inst. Radio. Eng., vol. 16, pp. 414-424, 1956.