本研究聚焦於製作和分析包括方形、圓形和五邊形的氮化鋁薄膜體聲波諧振器（FBAR）元件，並對其性能進行詳細比較和探討。這些元件皆採用背向空腔結構，以射頻磁控濺鍍法沉積氮化鋁薄膜作為壓電層，上下電極分別選用白金和鋁。首先，通過驗證氮化鋁薄膜的製程參數，確保其具有高品質的 C 軸優選取向和良好的機電耦合性能。接著，通過光罩設計改變上下電極的幾何形狀，製作不同形狀的 FBAR 元件，並分別測量和分析其頻率響應特性。
實驗結果顯示，方形 FBAR 元件在機電耦合係數（keff 2）、Q 值和 FOM 值方面表現最佳。方形元件的機電耦合係數達到 7.56%，Q 值和 FOM 值分別為 157.22 和 11.89，顯示其能量傳輸效率最高。然而，方形元件在主諧振頻率周圍存在一定的雜訊。圓形FBAR 元件的 Q 值和 FOM 值最低，分別為 81.1 和 4.36，但其製程良率和抗雜散模態的能力較強。五邊形 FBAR 元件則在雜散模態抑制方面表現良好，Q 值和 FOM 值分別為 128.64 和 9。
綜合而言，方形 FBAR 元件具優異的機電耦合性能和能量傳輸效率；圓形 FBAR元件具備高穩定性和抗雜訊性能；五邊形 FBAR 元件則在雜散模態抑制方面具備優勢。這些發現為未來 FBAR 元件的設計和製造提供了重要的理論和實驗支持。

The objective of this study is to examine the fabrication and analysis of aluminum nitride (AlN) thin-film bulk acoustic resonator (FBAR) devices with electrode shapes of square, circular, and pentagonal configurations, and with three distinct areas. Radio frequency (RF) magnetron sputtering was employed to deposit the AlN thin films with a thickness of 0.8 um. Subsequently, the S-parameters were measured using a network analyzer, and an equivalent circuit based on the MBVD model was then established.
The 22,500 μm² FBAR exhibited resonant characteristics, whereas no such characteristics were observed in the smaller FBARs, including the 8,100 μm² and 4,900 μm² models. The observed resonant characteristics of the three shapes exhibited a resonant frequency within the range of 4.4 GHz to 4.6 GHz, with an insertion loss of approximately 11.4 dB to 11.7 dB. Therefore the shapes of the FBAR electrodes have a negligible impact on the resonant frequency and insertion loss. However, the square FBAR device demonstrated the most optimal performance, exhibiting the highest electromechanical coupling coefficient (7.56%) and Q-factor (157.22).
It is probably that the benefits of the pentagonal configuration may only become evident in smaller electrode areas.However, the resonant characteristics of smallarea FBARs were not discernible due to the presence of considerable losses.

[1] 林威宇, "利用質量負載效應實現二階 FBAR 射頻濾波器之研究," 2022.
[2] X.-H. Xu, H.-S. Wu, C.-J. Zhang, and Z.-H. Jin, "Morphological properties of AlN piezoelectric thin films deposited by DC reactive magnetron sputtering," Thin solid films, vol. 388, no. 1-2, pp. 62-67, 2001.
[3] 董宴忻, "上電極面積大小及形狀對 FBAR 元件雜散模態的影響與分析," 2023.
[4] Y. Liu, Y. Cai, Y. Zhang, A. Tovstopyat, S. Liu, and C. Sun, "Materials, design, and characteristics of bulk acoustic wave resonator: A review," Micromachines, vol. 11, no. 7, p. 630, 2020.
[5] Z. Zhang, Y. Lu, W. Pang, D. Zhang, and H. Zhang, "A high performance C-band FBAR filter," in 2013 Asia-Pacific Microwave Conference Proceedings (APMC), 2013: IEEE, pp. 923-926.
[6] N. Ashraf, Y. Mesbah, A. Emad, and H. Mostafa, "Enabling the 5g: Modelling and design of high q film bulk acoustic wave resonator (fbar) for high frequency applications," in 2020 IEEE International Symposium on Circuits and Systems (ISCAS), 2020: IEEE, pp. 1-4.
[7] P. Joshi, L. Bhalotiya, S. Jaiswal, V. Butram, M. Hasamnis, and S. Upadhyay, "Design and modelling of thin film bulk acoustic resonator (FBAR) for RF application," Materials Today: Proceedings, vol. 73, pp. 50-53, 2023.
[8] A. Link, E. Schmidhammer, H. Heinze, M. Mayer, B. Bader, and R. Weigel, "Appropriate methods to suppress spurious FBAR modes in volume production," in 2006 IEEE MTT-S International Microwave Symposium Digest, 2006: IEEE, pp. 394-397.
[9] S. Taniguchi, T. Yokoyama, M. Iwaki, T. Nishihara, M. Ueda, and Y. Satoh, "7E-1 An air-gap type FBAR filter fabricated using a thin sacrificed layer on a flat substrate," in 2007 IEEE Ultrasonics Symposium Proceedings, 2007: IEEE, pp. 600-603.
[10] Y. Q. Fu et al., "Advances in piezoelectric thin films for acoustic biosensors, acoustofluidics and lab-on-chip applications," Progress in Materials Science, vol. 89, pp. 31-91, 2017.
[11] H. Cheng, Y. Sun, and P. Hing, "Microstructure evolution of AlN films deposited under various pressures by RF reactive sputtering," Surface and coatings technology, vol. 166, no. 2-3, pp. 231-236, 2003.
[12] C. Fei et al., "AlN piezoelectric thin films for energy harvesting and acoustic devices," Nano Energy, vol. 51, pp. 146-161, 2018.
[13] A. Ababneh, U. Schmid, J. Hernando, J. Sánchez-Rojas, and H. Seidel, "The influence of sputter deposition parameters on piezoelectric and mechanical properties of AlN thin films," Materials Science and Engineering: B, vol. 172, no. 3, pp. 253-258, 2010.
[14] J. H. Jung, Y. H. Lee, J. H. Lee, and H. C. Choi, "Vibration mode analysis of RF film bulk acoustic wave resonator using finite element method," in 2001 IEEE Ultrasonics Symposium. Proceedings. An International Symposium (Cat. No. 01CH37263), 2001, vol. 1: IEEE, pp. 847-850.
[15] R. Ruby, J. Larson, C. Feng, and S. Fazzio, "The effect of perimeter geometry on FBAR resonator electrical performance," in IEEE MTT-S International Microwave Symposium Digest, 2005., 2005: IEEE, pp. 217-220.
[16] J. F. Rosenbaum, "Bulk acoustic wave theory and devices," (No Title), 1988.
[17] P. Dineva et al., Piezoelectric materials. Springer, 2014.
[18] R. Gerhard, "The Beginnings of Piezoelectricity: A Study in Mundane Physics," Physics Today, vol. 60, no. 12, pp. 60-61, 2007, doi: 10.1063/1.2825075.
[19] L. Qin, Q. Chen, H. Cheng, and Q.-M. Wang, "Analytical study of dual-mode thin film bulk acoustic resonators (FBARs) based on ZnO and AlN films with tilted c-axis orientation," IEEE transactions on ultrasonics, ferroelectrics, and frequency control, vol. 57, no. 8, pp. 1840-1853, 2010.
[20] R. G. Polcawich and J. S. Pulskamp, "Additive processes for piezoelectric materials: Piezoelectric MEMS," in MEMS materials and Processes Handbook: Springer, 2011, pp. 273-353.
[21] K.-W. Tay, C.-L. Huang, and L. Wu, "Influence of piezoelectric film and electrode materials on film bulk acoustic-wave resonator characteristics," Japanese journal of applied physics, vol. 43, no. 3R, p. 1122, 2004.
[22] A. Khan, Z. Abas, H. S. Kim, and I.-K. Oh, "Piezoelectric thin films: an integrated review of transducers and energy harvesting," Smart Materials and Structures, vol. 25, no. 5, p. 053002, 2016.
[23] C. C. Ruppel, "Acoustic wave filter technology–a review," IEEE transactions on ultrasonics, ferroelectrics, and frequency control, vol. 64, no. 9, pp. 1390-1400, 2017.
[24] S. Mahon and R. Aigner, "Bulk acoustic wave devices–why, how, and where they are going," in CS Mantech Conference, 2007, pp. 15-18.
[25] H. Campanella, Acoustic wave and electromechanical resonators: concept to key applications. Artech House, 2010.
[26] C. P. Wen, "Coplanar waveguide: A surface strip transmission line suitable for nonreciprocal gyromagnetic device applications," IEEE Transactions on Microwave Theory and Techniques, vol. 17, no. 12, pp. 1087-1090, 1969.
[27] T. Chao, Introduction to semiconductor manufacturing technology. Prentice Hall New Jersey, 2000.
[28] N. Nor, Y. Jing, and N. Khalid, "Characteristics of film bulk acoustic wave resonator using different electrode materials," in AIP Conference Proceedings, 2021, vol. 2347, no. 1: AIP Publishing.
[29] M. Hara, J. Kuypers, T. Abe, and M. Esashi, "Surface micromachined AlN thin film 2 GHz resonator for CMOS integration," Sensors and Actuators A: Physical, vol. 117, no. 2, pp. 211-216, 2005.
[30] M.-A. Dubois and P. Muralt, "Properties of aluminum nitride thin films for piezoelectric transducers and microwave filter applications," Applied Physics Letters, vol. 74, no. 20, pp. 3032-3034, 1999.
[31] M. D. Terzieva, "Overview of bulk acoustic wave technology and its applications," Electrotechnica & Electronica (E+ E), vol. 51, 2016.
[32] N. Nor et al., "The influence of design parameters on the performance of FBAR in 15–19 GHz," in AIP conference proceedings, 2018, vol. 2045, no. 1: AIP Publishing.
[33] D. A. Feld, R. Parker, R. Ruby, P. Bradley, and S. Dong, "After 60 years: A new formula for computing quality factor is warranted," in 2008 IEEE Ultrasonics Symposium, 2008: IEEE, pp. 431-436.
[34] I. S. Uzunov, M. D. Terzieva, B. M. Nikolova, and D. G. Gaydazhiev, "Extraction of modified butterworth—Van Dyke model of FBAR based on FEM analysis," in 2017 XXVI international scientific conference electronics (ET), 2017: IEEE, pp. 1-4.
[35] C.-M. Yang, K. Uehara, S.-K. Kim, S. Kameda, H. Nakase, and K. Tsubouchi, "Highly c-axis-oriented AlN film using MOCVD for 5GHz-band FBAR filter," in IEEE Symposium on Ultrasonics, 2003, 2003, vol. 1: IEEE, pp. 170-173.
[36] Y. Zhang and D. Chen, Multilayer integrated film bulk acoustic resonators. Springer Science & Business Media, 2012.
[37] Q. Su, P. Kirby, E. Komuro, and R. Whatmore, "Edge supported ZnO thin film bulk acoustic wave resonators and filter design," in Proceedings of the 2000 IEEE/EIA International Frequency Control Symposium and Exhibition (Cat. No. 00CH37052), 2000: IEEE, pp. 434-440.
[38] Y. Kumar, J. Singh, G. Kumari, R. Singh, and J. Akhtar, "Effect of shapes and electrode material on figure of merit (FOM) of BAW resonator," in AIP Conference Proceedings, 2016, vol. 1724, no. 1: AIP Publishing.
[39] G. Iriarte, J. Rodriguez, and F. Calle, "Effect of substrate–target distance and sputtering pressure in the synthesis of AlN thin films," Microsystem technologies, vol. 17, pp. 381-386, 2011.
[40] M. Arif, M. Sauer, A. Foelske-Schmitz, and C. Eisenmenger-Sittner, "Characterization of aluminum and titanium nitride films prepared by reactive sputtering under different poisoning conditions of target," Journal of Vacuum Science & Technology A, vol. 35, no. 6, 2017.
[41] K. Biswas and S. Kal, "Etch characteristics of KOH, TMAH and dual doped TMAH for bulk micromachining of silicon," Microelectronics journal, vol. 37, no. 6, pp. 519-525, 2006.
[42] F. Engelmark, G. Fucntes, I. Katardjiev, A. Harsta, U. Smith, and S. Berg, "Synthesis of highly oriented piezoelectric AlN films by reactive sputter deposition," Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, vol. 18, no. 4, pp. 1609-1612, 2000.