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Fabrication and characterization of thickness mode piezoelectric micromachined ultrasonic transducer (Tm-pMUT) based on PMN-PZT

Title
Fabrication and characterization of thickness mode piezoelectric micromachined ultrasonic transducer (Tm-pMUT) based on PMN-PZT
Translated Title
PMN-PZT 압전 단결정 및 미세가공기술을 이용한 두께진동모드 초음파 트랜스듀서 어레이 제작 및 성능평가
Authors
Kang, Woo Jin
DGIST Authors
Kang, Woo Jin; Choi, Hong Soo; Hwang, Jae Youn
Advisor(s)
Choi, Hong Soo
Co-Advisor(s)
Hwang, Jae Youn
Issue Date
2016
Available Date
2016-02-12
Degree Date
2016. 2
Type
Thesis
Keywords
PiezoelectricMEMSPMN-PZTUltrasoundPiezoelectric micromachined ultrasonic transducer (pMUT)
Abstract
In this study, the lead magnesium niobate–lead zirconate titanate (PMN-PZT) single crystal based thickness mode piezoelectric micromachined ultrasonic transducer (Tm-pMUT) array was fabricated using microelectromechanical systems (MEMS) process. The PMN-PZT single crystal was grown by solid-state single crystal growth (SSCG) method. The inductively coupled plasma (ICP) etching was used to make a PMN-PZT based Tm-pMUT array. The ICP etching characteristics of PMN-PZT single crystal were investigated in a BCl3/Cl2/Ar gas mixture environment. The ICP etching parameters were RF power, chamber pressure, bias power, gas mixing ratio. The RF power was varied from 200 W to 1000 W. The bias power was controlled from 50 W to 450 W, and the gas flow rate was fixed as 20 sccm. The PMN-PZT surface was analyzed using X-ray photoelectron spectroscopy (XPS) to investigate the etching mechanism. The result showed that the BCl3/Cl2/Ar plasma increased etch selectivity ratio without decreasing etch rate of PMN-PZT single crystal and the physical etching was dominant. The sidewall angles was increased along the increase of the bias power. The optimized ICP etching conditions were BCl3/Cl2/Ar= 5/2/3 (10/4/6 sccm), 800 W RF power, 350 W bias power, 2 mTorr chamber pressure. The optimized ICP etching conditions gave a 107.6 nm/min etch rate and 4.22 etch selectivity ratio. Those optimized ICP conditions were used to fabricate the PMN-PZT based Tm-pMUT array. The PMN-PZT based Tm-pMUT array has 8 annular elements. The thickness of PMN-PZT single crystal was 300 m. The average resonance frequency and anti-resonance frequency were 2.66 (± 0.04) and 3.18 (± 0.03) MHz, respectively. The measured effective electromechanical coupling coefficient (keff2) was 30.05 %. These resonance frequency has high potential for ultrasound imaging applications. ⓒ 2016 DGIST
Table Of Contents
1. Introduction 8 -- 1.1 Background knowledge 10 -- 1.1.1 Dielectric material 10 -- 1.1.2 Piezoelectric materials 12 -- 1.2 Comparison between the material properHnd PZT ceramics 19 -- 1.3 Necessity of PMN-PZT ICP etching 20 -- 1.4 Annular array transducer 22 -- 1.5 The equivalent circuit of a piezoelectric vibrator 23 -- 1.6 Related research work 25 -- 1.6.1 Bulk piezoelectric transducer 25 -- 1.6.2 Membrane type piezoelectric micromachined ultrasonic transducer (pMUT) 26 -- 2. Design and Fabrications of PMN-PZT based Tm-pMUT array 27 -- 2.1 Fabrication of the PMN-PZT single crystal 27 -- 2.1.1 Grown PMN-PZT single crystal by using SSCG method 27 -- 2.1.2 Hysteresis loop of PMN-PZT single crystal 29 -- 2.2 Design of the PMN-PZT based Tm-pMUT array 31 -- 2.3 Optimization of inductively coupled plasma (ICP) etching conditions for PMN-PZT based Tm-pMUT array 33 -- 2.4 Fabrication Process of the PMN-PZT based Tm-pMUT array 36 -- 3. Experiment 41 -- 3.1 Impedance analysis of the PMN-PZT based Tm-pMUT array 41 -- 4. Results and Discussions 43 -- 4.1 PMN-PZT ICP etching results 43 -- 4.1.1 The etch rate and etch selectivity ratio results of PMN-PZT/Ni 43 -- 4.1.2 Effect of bias power on the sidewall angle of PMN-PZT single crystal 53 -- 4.1.3 The X-ray photoelectron spectroscopy (XPS) analysis results of PMN-PZT single crystal 54 -- 4.1.4 Discussion of PMN-PZT ICP etching 61 -- 4.2 Electrical characterization of the PMN-PZT based Tm-pMUT array 62 -- 4.2.1 Impedance analyzing of the kerfed type PMN-PZT based Tm-pMUT array 62 -- 4.2.2 Impedance analyzing of the kerfless type PMN-PZT based Tm-pMUT array 65 -- 4.2.3 Discussion on electrical characteristics of PMN-PZT based Tm-pMUT array 68 -- 5. Conclusions 69 -- REFERENCES 71
URI
http://dgist.dcollection.net/jsp/common/DcLoOrgPer.jsp?sItemId=000002229789
http://hdl.handle.net/20.500.11750/1422
DOI
10.22677/thesis.2229789
Degree
Master
Department
Robotics Engineering
University
DGIST
Files:
Collection:
Robotics EngineeringThesesMaster


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