本研究利用TSMC 0.35m 2P4M CMOS-MEMS標準製程開發電容式超聲波換能器(Capacitive Micromachined Ultrasonic Transducers, CMUTs)，電容式超聲波的特性為擁有較佳的接收靈敏度且易與CMOS-MEMS電路作整合。本研究主要結合雙電極、凹槽以及陣列式設計，雙電極設計可以利用偏壓的調整使得結構的電容間隙縮小以提升訊號；凹槽設計除了能降低薄膜剛性，使所需要的偏壓降低外，也可增加平均薄膜的位移，因此提升訊號強度；最後陣列式設計則是為了提升發送超聲波時的壓力以及接收超聲波時的訊號。
量測的結果顯示，在利用72個薄膜陣列所組成的雙電極電容式超聲波元件，其接收端在放大20dB後擁有460mV的電壓峰對峰值，其中心頻落在2MHz，比例頻寬為120%。在發送方面，元件未吸附前可產生約43.9kPa的超聲波壓力，中心頻在4.07MHz，比例頻寬為261%；當元件薄膜吸附在底電極後也擁有約4kPa的超聲波發送壓力，中心頻在8.07MHz，比例頻寬為85.8%。由於製程因素未將雙電極的特性表現出來，未來將改善製程及元件設計，相信可達到單一晶片上自發自收且整合電路之效能，以應用於生醫的檢測及造影成像。

[1] C.-M. Lin, ”Implementation of a human follicles assessment by ultrasound techniques,” Master thesis, Institute of Biomedical Engineering, National Cheng Kung University, Jun. 2008.

[2] K. T. Dussik, “Uber die moglichkeit hochfrequente mechanische schwingungen als diagnostisches hilfsmittel zu verwerten”, Z Neurol Psychiat, vol. 174, no. 1, pp. 153-168, Dec. 1942.

[3] I. Donald, J. Macvicar, and T. G. Brown, “Investigation of abdominal masses by pulsed ultrasound,” The Lancet, vol. 271, no. 7032, pp. 1188-1195, June 1958.

[4] D. G. McDonald and G. R. Leopold, “Ultrasound B-scanning in the differentiation of Baker’s cyst and thrombophlebitis,” Br J Radiol, vol. 45, no. 538, pp. 729-732, Oct. 1972.

[5] A.-S. Ergun, G.-G. Yaralioglu, and B.-T. Khuri-Yakub, “Capacitive micromachined ultrasonic transducers: theory and technology,” Journal of Aerospace Engineering, vol. 16, no. 2, pp. 76-84, April 2003.

[6] R. O. Guldiken, “Dual-electrode capacitive micromachined ultrasonic transducer for medical ultrasound applications,” Ph.D. thesis, Georgia Institute of Technology, Dec. 2008.

[7] S. Olcum, F. Yalcin Yamaner, A. Bozkurt, and A. Atalar, “Deep-collapse operation of capacitive micromachined ultrasonic transducers,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 58, no. 11, pp. 2475-2483, Nov. 2011.

[8] K.-K. Park, Ö. Oralkan, and B.-T. Khuri-Yakub, “A Comparison Between Conventional and Collapse-Mode Capacitive Micromachined Ultrasonic Transducers in 10-MHz 1-D Arrays,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 60, no. 6, pp. 1245-1255, Jun. 2013.

[9] P. K. Tang, P. H. Wang, M. L. Li and Michael S.-C. Lu, “Design and characterization of the immersion-type capacitive ultrasonic sensors fabricated in a CMOS process,” J. Micromechanics and Microengineering, vol. 21, no. 2, pp. 2475-2483 , Feb. 2011.

[10] Y.-S. Tien, P.-C. Ku, F.-Y. Lin, P.-C. Li, L.-H. Lu, P.-L. Kuo, and W.-C. Tian, “A low voltage CMOS-based capacitive micromachined ultrasonic sensors development”, 2012 IEEE Sensors Conference, Taipei, Taiwan, pp. 1810-1813. Oct. 2012.

[11] W.-C. Chen, M.-H. Li, Y.-C. Liu, W. Fang, and S.-S. Li,"A fully-differential CMOS-MEMS DETF oxide resonator with Q > 4,800 and positive TCF," IEEE Electron Device Letters, vol. 33, no. 5, pp. 721-723, May 2012.

[12] M. Shin, J.-S. Krause, P. DeBitetto, and R.-D. White, “Acoustic Doppler velocity measurement system using capacitive micromachined ultrasound transducer array technology,” Journal of the Acoustical Society of America, vol. 134, no. 2, pp.1011-1020, Aug. 2013.

[13] P. Osterberg, H. Yie, X. Cai, J. White, and S. Senturia, “Self-consistent simulation and modeling of electrostatically deformed diagrams,” 1994 IEEE Micro Electro Mechanical Systems, pp. 28-32, Jan. 1994.

[14] D. M. Schneider, J. Malibach, and E. Obermeir, “A new analytical solution for the load-deflection of square membranes,” Journal of Microelectromechanical System, vol. 4, no. 4, pp. 238-241, Dec. 1995.

[15] M. Rahman, J. Hernandez, S. Chowdhury, “An improved analytical method to design CMUTs with square diaphragms,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 60, no. 4, pp.834-845, Apr. 2013.

[16] A. Lohfink and P.-C. Eccardt, “Linear and nonlinear equivalent circuit modeling of CMUTs,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 52, no. 12, pp.2163-2172, Dec. 2005.

[17] M. Greenspaan, “Piston radiator: Some extensions of the theory,” Journal of the Acoustical Society of America, vol. 65, no. 3, pp.608-621, Mar. 1979.

[18] H. Köymen, A. Atalar, E. Aydoğdu, C. Kocabaş, H.-K. Oğuz, S. Olçum, A. Ozgurluk, A. Unlügedik, “An improved lumped element nonlinear circuit model for a circular CMUT cell,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 59, no. 8, pp.1791-1799, Aug. 2012.

[19] L.-L. Beranek, Acoustical Measurements, Acoustical Society of America, 1988.

[20] C.-B. Doody, X.-Y. Cheng, C.-A. Rich, D.-F. Lemmerhirt, and R.-D. White, “Modeling and characterization of CMOS-fabricated capacitive micromachined ultrasound transducer,” Journal of Microelectromechanical Systems, vol. 20, no. 1, pp.104-118, Feb. 2011.