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標題: | 利用聚對二甲苯製作電容式超音波換能器之研究 Fabrication of parylene based capacitive ultrasound transducers |
作者: | I-Chen Lai 賴怡辰 |
指導教授: | 施文彬(Wen-Pin Shih) |
關鍵字: | 電容式超音波換能器,聚對二甲苯,靜電力,微機電製程, capacitive micromachined ultrasound transducers (CMUT),parylene,electrostatic force,MEMS, |
出版年 : | 2013 |
學位: | 碩士 |
摘要: | 本論文利用聚對二甲苯製作電容式超音波換能器(CMUT),並探討圓形CMUT之機械與電特性。超音波換能器在醫療檢測應用上占重要位置且被廣泛運用。其中,電容式超音波換能器擁有微小、高敏感度、低成本、高阻抗匹配及高頻寬優點,為新型探頭發展技術 並有相當數量的研究發表。本論文首先分析圓形CMUT之振動行為,利用運動時位能變化推導位移公式並探討元件半徑及各薄膜上質點位移的關係。接著利用之前所推導出之位移公式推導出其機械阻抗。因CMUT為機電換能器,本論文亦分析其電特性,並推導其等效電路。Chapter 3介紹聚對二甲苯CMUT之結構設計,並用有限元素法針對所設計之結構與其共振頻做更進一步之分析,並決定CMUT尺寸。另外,CMUT之製程須利用黃光微影製程,第三章亦介紹本研究CMUT之光罩設計。本研究之光罩設計包括CMUT陣列、單顆CMUT、測試用懸臂樑。Chapter 4介紹聚對二甲苯CMUT之製作過程。本研究之CMUT利用黃光微影製程定義各層圖形、利用蒸鍍法(e-beam)沉積金屬電極、利用光阻當犧牲層製作CMUT的空腔、利用聚對二甲苯沉積法沉積CMUT薄膜、並利用反應離子蝕刻系統(RIE)去除多餘之聚對二甲苯。Chapter 4亦介紹CMUT製程之後的封裝過程。封裝過程包括塗佈銀膠於電極階梯部分已去除蒸鍍法所造成之階梯效應,並利用電線將電訊號連接出來,最後在沉積一層聚對二甲苯薄膜,使CMUT之空腔為真空狀態,如此一來可增加換能器之敏感度。Chapter 5針對所設計之聚對二甲苯CMUT進行量測與分析。首先,量測CMUT在不同偏壓下電容值並確認CMUT之電訊號可由外接電壓控制。接著使用雷射共軛焦顯微鏡量測薄膜在不同偏壓下之位移,並確認CMUT之薄膜可隨外接電壓產生位移。最後,在真空下利用網路分析儀量測CMUT在不同頻率下之阻抗,並推測本研究之CMUT的共振頻率在2.65 MHz ~ 2.85 MHz。 In this thesis parylene based capacitive ultrasound transducers was fabricated the electrical and mechanical characteristic of capacitive micromachined ultrasound transducer (CMUT) was analyzed. Ultrasound transducer plays a critical role and is widely used in current clinical applications. Capacitive micromachined ultrasound transducer is a newly developing technology in detector region and considerable number of study has been published. CMUT has lots of advantages such as micro scale dimension, high sensitivity, low fabrication expense, matching impedance to liquid and gas medium, and wide bandwidth. In this thesis, vibration characteristic of circular CMUT was analyzed. We derived the displacement equation of CMUT and analyzed the relationship between device radius, displacement and vibration frequency. We also used the displacement equation to derive the mechanical impedance of CMUT. Because CMUT is a mechanical versus electrical transducer, we also analyzed the CMUT’s electrical characteristic and derived the electrical equivalent circuit of CMUT. Then, the structure of parylene based CMUT was proposed. Relationship between CMUT’s structure and resonant frequency was analyzed, and dimension of CMUT was determined. CMUT was fabricated utilizing MEMS process, and patterns of each layer were defined using lithography process. There were CMUT array, single CMUT elements, testkey beams designed in each mask. The fabrication process of parylene based CMUT was proposed and tested. We used lithography technology to define the patterns of each layer. Electrodes were deposited using e-beam evaporation. CMUT’s cavity was defined by using photoresist as sacrificial material. Parylene was chosen as the vibration membrane of device. Redundant parylene was removed by RIE system. In packaging process, silver conductive grease was smeared on the step part of electrode pad to prevent the step-cover effect caused by e-beam evaporation process. Signal from electrodes was connected out by wires. To keep the cavity of CMUT in vacuum situation, the CMUT device was coated with another layer of parylene. Keeping cavity in vacuum environment could increase the sensitivity of CMUT. The fabricated CMUT was measured and analyzed. The capacitance of CMUT was measured with different DC bias voltages to demonstrate that the electrical signal could be controlled by controlling applied voltage. Membrane displacement of CMUT under different bias voltages was measured using confocal laser scanning microscopy. Finally, we tried to find out the resonant frequency of CMUT by deriving the impedance of device at different frequencies. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/62383 |
全文授權: | 有償授權 |
顯示於系所單位: | 機械工程學系 |
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