摘 要
與其它聲波元件相比較，彎曲平板波元件具較高的質量靈敏度、低傳播速度與較低的操作頻率等優點，所以特別適合應用於液態量測的環境；然而，傳統彎曲平板波元件通常具高插入損失及低製程良率。
為降低彎曲平板波元件插入損失及提升製程良率，本論文採用一種具1.5 μm矽溝槽反射閘極結構、高機電耦合係數之氧化鋅壓電薄膜及5 μm二氧化矽薄膜之彎曲平板波元件。探討反射閘極結構之數量與佈局位置對於降低插入損失及品質因子之影響。主要製程技術是運用體型微加工技術，且主要製程步驟包含六次薄膜沉積與五次黃光微影製程。
於最佳化氧化鋅之製程參數條件下(基板溫度200℃，射頻功率200 W，氣體流量比75%)，本論文成功開發出一種具高C軸取向之機電耦合係數為31.33%之氧化鋅壓電薄膜，且X光繞射角34.282o非常接近標準氧化鋅之X光繞射角之值34.422o。經由控制感測薄膜(ZnO/Au/Cr/SiO2/Si3N4)厚度於6.5 μm之下，元件製程良率可以提升且具較低的操作頻率(6.286 MHz)及高質量感測靈敏度(-113.63 cm2/g)。除此之外，搭配4對矽溝槽反射閘極結構與37.5 μm之元件佈局位置可有效降低插入損失(-40.854 dB)，且具有高品質因子(206)。

關鍵字：彎曲平板波；矽溝槽反射閘極結構；機電耦合係數；氧化鋅；體型微加工技術

Abstract
Compared with the other micro acoustic wave devices, the flexural plate-wave (FPW) device is more suitable for being used in liquid-sensing applications due to its higher mass sensitivity, lower phase velocity and lower operation frequency. However, conventional FPW devices usually present a high insertion loss and low fabrication yield.
To reduce the insertion loss and enhance the fabrication yield of FPW device, a 1.5 μm-thick silicon-trench reflective grating structure (RGS), a high electromechanical coupling coefficient ZnO thin-film and a 5 μm-thick silicon oxide membrane substrate are adopted in this research. The influences of the amount of silicon trench and the distance between inter-digital transducer (IDT) and RGS on the insertion loss and quality factor of FPW device are investigated. The main fabrication technology adopted in the study is bulk micromachining technology and the main fabrication steps include six thin-film deposition and five photolithography processes.
Under the optimized conditions of the sputtering deposition processes (200℃ substrate temperature, 200 W radio-frequency power and 75% gas flow ratio), a high C-axis (002) orientation ZnO piezoelectric thin-film with 31.33% electromechanical coupling coefficient can be demonstrated. The peak of XRD intensity of the standard ZnO film occurs at diffraction angle 2θ = 34.422°, which matches well with our results (2θ = 34.282°). By controlling the thickness of ZnO/Au/Cr/SiO2/Si3N4 sensing membrane less than 6.5 μm-thick, the fabrication yield of FPW device can be improved and a low operation frequency (6.286 MHz) and high mass sensitivity (-113.63 cm2 / g) can be achieved. In addition, as the implemented FPW device with four silicon trenches RGS and 37.5 μm distance between IDT and RGS, a low insertion loss (-40.854 dB) and very high quality factor (Q=206) can be obtained.

Keywords：flexural plate-wave; silicon-trench reflective grating structure; electromechanical coupling coefficient; ZnO; bulk micromachining technology

目 錄
摘 要…… I
Abstract… II
致 謝…… IV
目 錄…… V
圖 次…… VIII
表 次…… X
第一章 緒論 1
1-1 前言與研究動機 1
1-2 文獻回顧 2
1-2-1 剪應力(Thickness shear mode, TSM)振盪器 3
1-2-2 表面聲波(Surface acoustic wave, SAW)感測器 3
1-2-3 剪力水平板波(Shear horizontal acoustic plate mode, SH-APM)感測器 5
1-2-4 彎曲平板波(Flexural plate wave, FPW)感測器 6
第二章 FPW元件之材料分析與理論 11
2-1 壓電效應於FPW元件之應用 11
2-1-1 壓電效應 11
2-1-2 壓電材料 13
2-2 氧化鋅壓電薄膜晶格結構與特性 14
2-3 氧化鋅壓電薄膜沉積方法與薄膜沉積原理 16
2-3-1 氧化鋅壓電薄膜沉積方式選擇 16
2-3-2 氧化鋅壓電薄膜沉積原理 16
2-4 反應性射頻磁控濺鍍原理 17
2-5 X 光繞射(X-Ray Diffraction, XRD)分析 18
2-6 金屬指叉轉換器之等效電路分析 21
2-7 反射閘極結構理論 25
2-7-1 反射閘極週期 27
2-7-2 反射閘極對數之原理 27
2-7-3 反射閘極與IDT之間距離之關係 27
2-8 元件量測技術 29
2-9 掃描式電子顯微鏡分析 30
2-10 元件質量靈敏度之理論推導 31
第三章 具矽溝槽反射閘極結構設計之FPW元件 32
設計與實驗方法 32
3-1 具矽溝槽反射閘極結構設計之FPW感測元件設計 32
3-1-1 FPW元件之光罩佈局設計 32
3-1-2 具矽溝槽反射閘極結構之FPW元件之光罩佈局設計規範 35
3-2 具矽溝槽反射閘極結構之FPW元件製作 37
3-2-1 具矽溝槽反射閘極結構之FPW元件製作流程 37
3-2-2 具矽溝槽反射閘極結構之FPW元件製作方法 38
第四章 結果與討論 44
4-1 氧化鋅壓電薄膜之材料特性分析 44
4-1-1 氣體流量比對氧化鋅壓電薄膜之影響 46
4-1-2 射頻濺鍍功率對氧化鋅壓電薄膜之影響 47
4-1-3 基板溫度對氧化鋅壓電薄膜之影響 48
4-2 具矽溝槽反射閘極結構之彎曲平板波元件開發 49
4-2-1 離軸心之距離對機電耦合係數(K2)之影響 50
4-2-2 具矽溝槽反射閘極結構之FPW元件特性量測結果與分析 51
4-2-3 FPW感測器固態負載下之量測結果與分析 55
第五章 結論與未來展望 62
5-1 結論 62
5-2 未來展望 63
參考文獻.. 65

參考文獻
[1] 微機電系統技術與應用，行政院國家科學委員會精密儀器發展中心出版，2003。
[2] D. S. Ballantine and D. Stephen, “Acoustic wave sensor: theory, design, and physico-chemical applications,” San Diego, Academic Press, Inc., 1997.
[3] R. W. Cernosek, “An overview of acoustic wave devices for chemical & biological sensing, biological detection, and materials characterization,” Solid-State Sensor Lecture, Auburn University, Auburn, AL, 2002.
[4] L. Rayleigh, “On waves propagated along the plane surface of an elastic solid,” Proc. London Math. Soc. vol. 17, pp. 4, 1885.
[5] 李其源，蝕刻晶片厚度即時監控之新穎方法，國立台灣大學機械工程研究所博士論文，2004。
[6] 吳德春，薄膜式表面聲波元件之製作與分析，中原大學電子工程學系碩士論文，2002。
[7] D. W. Galipeau, P. R. Story, K. A. Vetelino and R. D. Mileham, “Surface acoustic wave microsensors and applications,” Smart Mater. Struct., vol. 6, pp. 658-667, 1997.
[8] A. Pohl, “A review of wireless SAW sensors,” IEEE Trans. Ultras. Ferr. Freq. Contr., vol. 47, pp. 317-332, 2000.
[9] B. Drafts, “Acoustic wave technology sensors,” IEEE Transaction On Microwave Theory and Techniques, vol. 49, no. 4, 2001.
[10] M. I. Rocha-Gaso, C. M. Iborra, A. M. Baides and A. A. Vives, “Surface generated acoustic wave biosensors for the detection of pathogens,“ Sensors, vol. 9, pp. 5740-5769, 2009.
[11] M. J. Velekoop, “Acoustic wave sensors and their technology,” Ultrasonics, vol. 36, pp. 7-14, 1998.
[12] M. E. Motamedi and R. M. White, “Acoustic sensor in semiconductor sensor,” John Wiely & Sons, Inc., New York, 1994.
[13] M. S. Weinberg, B. T. Cunningham and C. W. Clapp, “Modeling flexural plate wave device,” J. Microelectromech. Syst., vol. 9, no. 3, pp. 370- 379, 2000.
[14] Q. X. Su, P. Kirby, E. Komuro, M. Imura, Q. Zhang and R. Whatmore, “Thin film bulk acoustic resonators and filters using ZnO and Lead Zirconium Titanate thin films,” IEEE Transactions on microwave theory and techniques, vol. 49, no. 4, pp. 769-778, 2001.
[15] T. Nishihara, T. Yokoyama, T. Miyashita and Y. Satoh, “High performance and miniature thin film bulk acoustic wave filters for 5 GHz,” IEEE Ultrasonics Symposium, vol. 1, pp. 969-972, 2002.
[16] 鄒一德，透明氧化鋅之薄膜電晶體技術開發研究，國立交通大學光電工程系顯示科技研究所碩士論文，2006。
[17] 王瑞琪，新穎氧化鋅奈米材料的成長與光電性質，國立成功大學材料科學及工程研究所博士論文，2006。
[18] 林素霞，氧化鋅薄膜的特性改良及應用之研究，國立成功大學材料科學及工程研究所博士論文，2003。
[19] Y. Yoshino, T. Makino, Y. Katayama and T. Hata, “Optimization of zinc oxide thin film for surface acoustic wave filters by ratio frequency sputtering,” Vacuum, vol. 59, pp. 538-545, 2000.
[20] B. T. khuri-Yakub, J. G. Smits and T. Barbee, “Reactive magnetron sputtering of ZnO,” J. Appl. Phys., vol. 52, issue 7, pp. 4772-4774, 1981.
[21] 郭益男，以反應濺鍍法製備氧化鋅薄膜與摻雜鋁之研究，國立中山大學材料科學與工程研究所碩士論文，2004。
[22] 蔡來福，以電漿輔助化學氣相沉積法室溫成長氧化鋅薄膜之研究，國立中央大學光電科學研究所碩士論文，2002。
[23] 歐天凡，沉積條件對氮化鋁薄膜壓電係數及機電耦合係數之影響，國立中山大學電機工程研究所碩士論文，2004。
[24] H. Zhang and E. S. Kim, “Micromachined acoustic resonant mass sensor,” IEEE Microelectromechanical Systems, vol. 14, pp. 699-706, 2005.
[25] L. A. Zepeda-Ruiz and D. J. Srolovitz, “Effects of ion beams on the early stages of MgO growth,” J. Appl. Phys., vol. 91, pp. 10169-10181, 2002.
[26] T. Ohwaki, T. Yoshida, S. Hashimoto, H. Hosokawa, Y. Mitsushima and Y. Taga, “Preferred orientation in Ti films sputter-deposited on SiO2 glass: The role of water chemisorption on the substrate,” Jpn. J. Appl. Phys., vol. 36, pp. L154-L157, 1997.
[27] E. J. Bienk, H. Jensen and G. Sorensen, “The influence of the reactive gas flow on the properties of AlN sputter-deposited films,” Mater. Sci. and Eng. A, vol. 140, pp. 696-701, 1991.
[28] 汪建民主編，材料分析，中國材料科學學會。
[29] W.R. Smith, H.M. Gerard, J.H. Collins, T.M. Reeder and H.J. Shaw, “Analysis of interdigital surface wave transducers by use of equivalent circuit model,” IEEE Trans. Microwave Theory and Techniques, vol. MTT-17, no. 11, pp. 856-864, 1969.
[30] 林俊甫，雙埠表面聲波濾波器的模擬與量測，國立成功大學機械工程學研究所碩士論文，2003。
[31] S. G. Joshi, B. D. Zaitsev and I. E. Kuznetsova, “Reflection of plate acoustic waves produced by a periodic array of mechanical load strips or grooves,” IEEE Trans. Ultras. Ferr. Freq. Contr., vol. 49, no. 12, pp. 1730-1734, 2000.
[32] C. Y. Huang, J. H. Sun and T. T. Wu, “A two-port ZnO/silicon Lamb wave resonator using phononic crystals,” Appl. Phys. Lett., vol. 97, issue 3, 2010.
[33] 吳朗，表面生波SAW化學感測器，Chemistry (The Chinese CHEM.SOC, Taipei), pp. 279-286, 2001。
[34] R. H. Tancrell and M. G. Holland, “Acoustic surface wave filters,“ Proc. IEEE, pp. 393-409, 1971.
[35] C. R. Aita, A. J. Purdes, K. L. Lad and P.D. Funkenbusch, “The effect of O2 on reactively sputtered zinc oxide,” J. Appl. Phys., vol. 51, issue 10, pp. 5533-5536, 1980.
[36] C. R. Aita, R. J. Lad and T. C. Tisone, “The effect of rf power on reactively sputtered zinc oxide,” J. Appl. Phys., vol. 51, issue 12, pp. 6405-6410, 1980.
[37] J. B. Lee, H. J. Kim and S. G. Kim, “Deposition of ZnO thin films by magnetron sputtering for a film bulk acoustic resonator,” Thin Solid Film, vol. 423, pp. 262, 2003.