CMOS-MEMS超音波感測器之設計與製作｜國立清華大學博碩士論文庫

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研究生：	陳孟輝 MENG-HUI CHEN
論文名稱：	CMOS-MEMS超音波感測器之設計與製作 Design and fabrication of CMOS-MEMS ultrasonic sensors
指導教授：	盧向成 Lu, Shiang-Cheng
口試委員:
學位類別：	碩士 Master
系所名稱：	電機資訊學院 - 電子工程研究所 Institute of Electronics Engineering
論文出版年：	2007
畢業學年度：	95
語文別：	英文
論文頁數：	53
中文關鍵詞：	微機電系統、電容式感測、薄膜
外文關鍵詞：	MEMS, Capacitive sensing, Membrane
相關次數：	點閱：4 下載：0
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我們在這篇論文呈現出以CMOS微加工技術製造在空氣中的電容式感測超音波。因為在空氣中，電容的聲波阻抗(結構阻抗)對於傳輸超音波能量所需要考慮的阻抗匹配來說十分重要，所以薄膜的結構設計是成功量測的主要關鍵，利用CoventorWare軟體，結構的阻抗和震盪位移都可以模擬得來。製作薄膜採用後微加工技術，先做金屬的濕蝕刻，後再做反應性離子蝕刻，完成後的薄膜為一直徑65μm的圓盤，由四根橫樑支撐，上下電極形成的感測電容為35fF。在電容偏壓為10伏特下，感測到的訊號為3.25μV，計算後薄膜受到的正向力為0.69nNt，或是0.1394Pa。

We presents a CMOS micromachined capacitive sensor for detection of acoustic pressure transmitted through the air in this thesis. Due to the membrane mechanical impedance (acoustic impedance) is important in impedance match during the transition of ultrasonic energy from air into the membrane, the simulation and design of the membrane structure becomes crucial of successful sensing. By using CoventorWare software, the membrane impedance and harmonic vibrations is simulated. The post micromachining steps of the membrane performed at chip level start with a sacrificial metal etch, followed by a dielectric reactive ion etch. The fabricated device has a suspended plate of 65 μm in diameter with four support beams, producing an initial sensing capacitance of 35 fF. The measured sensor output is 3.25 μV at an electrode bias of 10 V while the corresponding acoustic force and pressure acting on the sensor are 0.69 nN and 0.1394 Pa, respectively.

Abstract    I
Acknowledgement    III
Contents    IV
List of Figures    V
List of Table    VII
Chapter1    1
1.1 Motivation    1
1.2 Literature survey    2
1.3 Organization of this thesis    5
Chapter2    6
2.1 Introduction of the CMUT structure    7
2.2 Theory for parallel capacitor    8
2.2.1 Membrane collapse voltage    8
2.2.2 Spring softening    14
2.2.3 Membrane vibration and its equivalent circuit    15
2.3 Simulation of mechanical impedance and spring constant    19
2.4 Design and simulation of the sensing circuit    32
Chapter 3    37
3.1Post-CMOS Micromachining Process    37
3.2 Sensing circuit measurement    41
3.3 Acoustic Wave Measurement    43
Chapter4    49
Reference    51

List of Figures
Figure 1 Photograph of spring, 3-D rendered ultrasound    3
Figure 2 Photograph of Palmaz-Schatz stent, deployed, 3-D rendered ultrasound    4
Figure 3 (a) Top view of the 64-element CMUT ring array. (b) Magnified view of individual element. [3]    4
Figure 4  A conceptual drawing of an integrated intravascular ultrasound imaging system. [3]    5
Figure 9 Partial electrical equivalent circuit of the membrane.    16
Figure 10 Electrical equivalent circuit of membrane    17
Figure 11 Electrical equivalent circuit of membrane.    17
Figure 12 Electrical equivalent circuit of membrane when Zm<<Za    18
Figure 13 The simplified process file.    19
Figure 14 The CoventorWar simulation process    21
Figure 15 The simulation result of membrane 3D model.    22
Figure 16 The cross section diagram of the membrane.    23
Figure 17 Simulation result of membrane natural frequency    26
Figure 18 The membrane 1 harmonic response.    27
Figure 19 Harmonic response of membrane 2.    28
Figure 20 Harmonic response membrane 3.    29
Figure 21 Harmonic response of membrane 4.    30
Figure 22 The sketch of the membrane mechanical impedance.    31
Figure 23 Magnified plot of the mechanical impedance.    31
Figure 24 The schematic of the sensing circuit.    33
Figure 25 The frequency response of the sensing circuit.    35
Figure 26 Layout of the sensing circuit.    36
Figure 27 The process flow of the post CMOS process.    39
Figure 28 The membrane structure after post-CMOS micromachining process.    40
Figure 29 The white light interferometer measurement.    40
Figure 30 Measured result of the first pole shift.    42
Figure 31 The frequency response of the sensing circuit.    42
Figure 33 The face to face set up.    46
Figure 34 The output spectrum measurement at a resolution bandwidth of 1 Hz.    46
Figure 35 The sensor output by gradually increasing the dc voltage on the electrode to 300 V.    47
Figure 36 The output decreases for Vgs values increasing from 0.1 V to 0.7 V.    47
Figure 37 The output signal increase linearly with respect to the emitter driving voltage.    48

List of Tables
Table 1 Simulation performance of the sensing circuit.    35
Table 2 Measured result of the first pole shift.    42

                                

[1] D.T. Yeh, O¨ mer Oralkan, I. O. Wygant, M.O’Donnell, and B.T. Khuri-Yakub, “3-D Ultrasound Imaging Using Forward Viewing CMUT Ring Arrays for intravascular and Intracardiac Applications,” in Proc.IEEE Ultrason. Symp.,pp.783-786, 2005
[2] Y. Wang, D. Stephens, and M. O’Donnell, “Initial results from a forward viewing ring-annular ultrasound array for intravascular imaging,” in Proc. IEEE Ultrason. Symp., vol. 1, Oct. 2003, pp. 212–215.
[3] U. Demirci, A. S. Ergun, O¨ . Oralkan, M. Karaman, and B. T. Khuri- Yakub, “Forward-viewing CMUT arrays for medical imaging.” IEEE Trans. Ultrason., Ferroelect., Freq. Contr., vol. 51, no. 7, pp. 887–895, July 2004.
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[5] O¨ . Oralkan, A. S. Ergun, J. A. Johnson, U. Demirci, M. Karaman, K. Kaviani, T. H. Lee, and B. T. Khuri-Yakub, “Capacitive micromachined ultrasonic transducers: Next-generation arrays for acoustic imaging?” IEEE Trans. Ultrason., Ferroelect., Freq. Contr., vol. 49, no. 11, pp. 1596–1610, Nov. 2002.
[6] B. Bayram, E. Hæggstr¨om, G. G. Yaralioglu, and B. T. Khuri-Yakub, “A new regime for operating capacitive micromachined ultrasonic transducers,” IEEE Trans. Ultrason., Ferroelect., Freq. Contr., vol. 50, no. 9, pp. 1184–1190, Sept. 2003.
[7] X. Jin, I. Ladabaum, and B. T. Khuri-Yakub, “The Microfabrication of CapacitiveUltrasonic Transducers”, Journal of microelectromechanical systems, vol. 7, no. 3, pp. 295-302, 1998.
[8] M. I. Haller and B. T. Khuri-Yakub, “A surface micromachined electrostaticultrasonic air transducer,” IEEE Trans. Ultrason., Ferroelect.,Freq. Contr., vol. 43, no. 1, pp. 1–6, 1996.
[9] X.C. Jin, B.T. Ehuri-Yakub, F.L. Degertekin, I. Ladabaum, and S. Calmes, “Micromachined capacitive ultrasonic immersion transducer for medical imaging,” Engineering in Medicine and Biology Society, 1998. Proceedings of the 20th Annual International Conference of the IEEE Volume 2, 29 Oct.-1 Nov. 1998 Page(s):779 - 782 vol.2 Digital Object Identifier 10.1109/IEMBS.1998.745545
[10] Ergun, A.S.; Cheng, C.-H.; Demirci, U.; Khuri-Yakub, B.T.,” Fabrication and characterization of 1-dimensional and 2-dimensional Capacitive Micromachined Ultrasonic Transducer (CMUT) arrays for 2-dimensional and volumetric ultrasonic imaging,” Oceans '02 MTS/IEEE Volume 4, 29-31 Oct. 2002 Page(s):2361-2367, vol.4.
[11] B. G. Streetman, S.Banerjee, Solid State Electronic Devices,5th ed., chap. 6, Prentice Hall, 2000.

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