超音波觸覺為一種觸覺反饋技術，利用高強度超音波的聚焦刺激人體皮膚以形成觸覺，其具有高解析度與非接觸式等優點，適合與VR/AR技術或3C產品結合。
目前超音波觸覺技術可透過傳統傳感器組成的模組來實現，然而現有模組因傳感器體積大，不易與可攜式產品結合，因此本研究提出使用壓電式微型超音波傳感器(pMUT)取代傳統傳感器，不僅可以大幅縮小整體尺寸，且pMUT相較電容式微型超音波傳感器(cMUT)最大優勢在於不需要直流偏壓即可驅動，功耗相對較低，適合與可攜式產品結合。
本研究透過圓盤分析模型與有限元素模型進行模擬，以設計響應頻率為40kHz時pMUT之尺寸，結構部分選用鋯鈦酸鉛(PZT)作為pMUT之壓電層，並嘗試射頻濺鍍法、脈衝雷射沉積法及溶膠凝膠法三種製備方法，透過調整退火參數製備出具有良好結晶情形及壓電特性的PZT，再將此PZT薄膜應用於整個pMUT製程中，以絕緣層上覆矽(SOI)作為基板與pMUT結構層，依序沉積下電極、PZT、上電極，最後進行背蝕刻形成空腔。
本研究製備出的pMUT經雷射都卜勒振動儀(LDV)分析其響應頻率，接近目標頻率40kHz，對單顆pMUT輸入脈衝驅動訊號，藉由高頻麥克風量測到0.227Pa的聲壓，透過陣列模擬可以輸出足以產生觸覺之聲壓，證明此pMUT未來有機會應用於超音波觸覺技術中。

Ultrasound haptics is a contactless tactile feedback method that create tactile sensation by focusing high-intensity ultrasound on human skin. This technique could be a great candidate to provide tangible feedback for virtual/augmented/mix reality and 3D hologram because of its capability to generate tactile feelings in designate locations.
Recently, ultrasound haptics have been realized using phased array composed of commercial ultrasonic transducers. However, existing air-coupled ultrasound transducers are too bulky to integrate with consumer electronics like monitors or cell phones which limits the feasibility of applying ultrasonic haptic feedback in daily life. Therefore, in this study, a piezoelectric micromachined ultrasonic transducer (pMUT) with small size and low power consumption is proposed to replace the traditional transducer.
The resonance frequency of proposed pMUT was 40kHz, and the radius of the it was designed by circular plate model and finite element model. The stacking sequence of proposed pMUT was bottom electrode, piezoelectric layer, and top electrode on a SOI wafer. To achieve better performance, PZT was selected as piezoelectric layer, and three different fabrication methods including RF sputtering, pulsed laser deposition and sol-gel deposition were compared to find the optimal fabrication process. The cavity of the pMUT was formed by releasing a circular membrane with deep reactive ion etching.
Finally, the resonance frequency of the pMUT was 32.9kHz which closed to the simulation result and the acoustic pressure of single pMUT was 0.227Pa at 70Vp-p. Although the measured results shows that the developed pMUT could not reach required acoustic pressure in a reasonable array dimension, this thesis has successfully demonstrated a pMUT platform including optimized design procedures, characterization techniques, and fabrication process.

[1] T. Iwamoto, D. Akaho, and H. Shinoda, "High resolution tactile display using acoustic radiation pressure," in SICE Annual Conference 2004, August 4, 2004 - August 6, 2004, Sapporo, Japan, 2004: Society of Instrument and Control Engineers (SICE), pp. 2105-2110.
[2] T. Iwamoto, T. Maeda, and H. Shinoda, "Focused ultrasound for tactile feeling display," in Proc. 2001 ICAT, 2001, pp. 121-126.
[3] I. Rakkolainen, E. Freeman, A. Sand, R. Raisamo, and S. Brewster, "A Survey of Mid-Air Ultrasound Haptics and Its Applications," (in eng), IEEE Trans Haptics, vol. Pp, Aug 24 2020.
[4] T. Iwamoto, M. Tatezono, and H. Shinoda, "Non-contact method for producing tactile sensation using airborne ultrasound," in 6th International Conference on Haptics: Perception, Devices and Scenarios, EuroHaptics 2008, June 10, 2008 - June 13, 2008, Madrid, Spain, 2008, vol. 5024 LNCS: Springer Verlag, pp. 504-513.
[5] T. Hoshi, T. Iwamoto, and H. Shinoda, "Non-contact tactile sensation synthesized by ultrasound transducers," in 3rd Joint EuroHaptics Conference and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems, World Haptics 2009, March 18, 2009 - March 20, 2009, Salt Lake City, UT, United states, 2009: IEEE Computer Society, pp. 256-260.
[6] T. Carter, S. A. Seah, B. Long, B. Drinkwater, and S. Subramanian, "UltraHaptics: Multi-point mid-air haptic feedback for touch surfaces," in 26th Annual ACM Symposium on User Interface Software and Technology, UIST 2013, October 8, 2013 - October 11, 2013, St. Andrews, United kingdom, 2013: Association for Computing Machinery, pp. 505-514.
[7] L. Corenthy et al., "Touchless tactile displays for digital signage: mid-air haptics meets large screens," in 2018 CHI Conference on Human Factors in Computing Systems, CHI EA 2018, April 21, 2018 - April 26, 2018, Montreal, QC, Canada, 2018, vol. 2018-April: Association for Computing Machinery, p. ACM SIGCHI.
[8] S. Rumelin, T. Gabler, and J. Bellenbaum, "Clicks are in the air: How to support the interaction with floating objects through ultrasonic feedback," in 9th ACM International Conference on Automotive User Interfaces and Interactive Vehicular Applications, AutomotiveUI 2017, September 24, 2017 - September 27, 2017, Oldenburg, Germany, 2017: Association for Computing Machinery, pp. 103-108.
[9] C. Kervegant, F. Raymond, D. Graeff, and J. Castet, "Touch hologram in mid-air," in ACM SIGGRAPH 2017 Emerging Technologies - International Conference on Computer Graphics and Interactive Techniques, SIGGRAPH 2017, July 30, 2017 - August 3, 2017, Los Angeles, CA, United states, 2017: Association for Computing Machinery, p. ACM Special Interest Group on Computer Graphics and Interactive Techniques (SIGGRAPH).
[10] Y. A. Pishchalnikov, O. Sapozhnikov, and T. Sinilo, "Increase in the efficiency of the shear wave generation in gelatin due to the nonlinear absorption of a focused ultrasonic beam," Acoustical Physics, vol. 48, no. 2, pp. 214-219, 2002.
[11] C. Hedberg and H. Gazisaeidi, "Variation of High Power Air Transducer " in Proceedings of Symposium on Ultrasonic Electronics, 2006, vol. 27: Institute for Ultrasonic Elecronics, pp. 199-200.
[12] M. Ito, D. Wakuda, S. Inoue, Y. Makino, and H. Shinoda, "High spatial resolution midair tactile display using 70 kHz ultrasound," in 10th International Conference on Haptics: Perception, Devices, Control, and Applications, EuroHaptics 2016, July 4, 2016 - July 7, 2016, London, United kingdom, 2016, vol. 9774: Springer Verlag, pp. 57-67.
[13] R. Kapoor, S. Ramasamy, A. Gardi, R. Van Schyndel, and R. Sabatini, "Acoustic sensors for air and surface navigation applications," Sensors (Switzerland), vol. 18, no. 2, 2018.
[14] L. R. Manfredi et al., "The Effect of Surface Wave Propagation on Neural Responses to Vibration in Primate Glabrous Skin," (in English), PLoS One, Article vol. 7, no. 2, p. 10, Feb 2012, Art no. e31203.
[15] W. Frier et al., "Using spatiotemporal modulation to draw tactile patterns in mid-air," in 11th International Conference on Haptics: Science, Technology, and Applications, EuroHaptics 2018, June 13, 2018 - June 16, 2018, Pisa, Italy, 2018, vol. 10893 LNCS: Springer Verlag, pp. 270-281.
[16] T. Romanus, S. Frish, M. Maksymenko, W. Frier, L. Corenthy, and O. Georgiou, "Mid-air haptic bio-holograms in mixed reality," in 2019 IEEE International Symposium on Mixed and Augmented Reality Adjunct (ISMAR-Adjunct), 2019: IEEE, pp. 348-352.
[17] M. Marchal, G. Gallagher, A. Lécuyer, and C. Pacchierotti, "Can Stiffness Sensations be Rendered in Virtual Reality Using Mid-air Ultrasound Haptic Technologies?," in International Conference on Human Haptic Sensing and Touch Enabled Computer Applications, 2020: Springer, pp. 297-306.
[18] P. Gijsenbergh et al., "Characterization of polymer-based piezoelectric micromachined ultrasound transducers for short-range gesture recognition applications," Journal of Micromechanics and Microengineering, vol. 29, no. 7, p. 074001, 2019.
[19] R. Atif et al., "Solution Blow Spinning of Polyvinylidene Fluoride Based Fibers for Energy Harvesting Applications: A Review," Polymers, vol. 12, no. 6, p. 1304, 2020.
[20] A. Jbaily and R. W. Yeung, "Piezoelectric devices for ocean energy: a brief survey," Journal of Ocean Engineering and Marine Energy, vol. 1, no. 1, pp. 101-118, 2015.
[21] N. Soin, S. Anand, and T. Shah, "Energy harvesting and storage textiles," in Handbook of Technical Textiles: Elsevier, 2016, pp. 357-396.
[22] S. J. Rupitsch, Piezoelectric sensors and actuators. Springer, 2019.
[23] Y. Qiu et al., "Piezoelectric micromachined ultrasound transducer (PMUT) arrays for integrated sensing, actuation and imaging," Sensors, vol. 15, no. 4, pp. 8020-8041, 2015.
[24] F. Akasheh, J. D. Fraser, S. Bose, and A. Bandyopadhyay, "Piezoelectric micromachined ultrasonic transducers: Modeling the influence of structural parameters on device performance," IEEE transactions on ultrasonics, ferroelectrics, and frequency control, vol. 52, no. 3, pp. 455-468, 2005.
[25] F. Akasheh, T. Myers, J. D. Fraser, S. Bose, and A. Bandyopadhyay, "Development of piezoelectric micromachined ultrasonic transducers," Sensors and Actuators A: Physical, vol. 111, no. 2-3, pp. 275-287, 2004.
[26] G.-L. Luo, Y. Kusano, M. N. Roberto, and D. A. Horsley, "High-Pressure Output 40 kHz Air-Coupled Piezoelectric Micromachined Ultrasonic Transducers," in 32nd IEEE International Conference on Micro Electro Mechanical Systems, MEMS 2019, January 27, 2019 - January 31, 2019, Seoul, Korea, Republic of, 2019, vol. 2019-January: Institute of Electrical and Electronics Engineers Inc., pp. 787-790.
[27] A. Halbach et al., "Display Compatible PMUT Array for Mid-Air Haptic Feedback," in 20th International Conference on Solid-State Sensors, Actuators and Microsystems and Eurosensors XXXIII, TRANSDUCERS 2019 and EUROSENSORS XXXIII, June 23, 2019 - June 27, 2019, Berlin, Germany, 2019: Institute of Electrical and Electronics Engineers Inc., pp. 158-161.
[28] A. Hajati, "Ultra Wide-Bandwidth Micro Energy Harvester," Massachusetts Institute of Technology, 2010.
[29] F. Martin, P. Muralt, M.-A. Dubois, and A. Pezous, "Thickness dependence of the properties of highly c-axis textured AlN thin films," Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, vol. 22, no. 2, pp. 361-365, 2004.
[30] M.-H. Zhao, Z.-L. Wang, and S. X. Mao, "Piezoelectric characterization of individual zinc oxide nanobelt probed by piezoresponse force microscope," Nano Letters, vol. 4, no. 4, pp. 587-590, 2004.
[31] M. Vacca et al., "Electric clock for NanoMagnet logic circuits," in Field-Coupled Nanocomputing: Springer, 2014, pp. 73-110.
[32] M. Cueff et al., "Influence of the crystallographic orientation of Pb (Zr, Ti) O 3 films on the transverse piezoelectric coefficient d 31," in 2011 IEEE International Ultrasonics Symposium, 2011: IEEE, pp. 1948-1951.
[33] S. Pramanik, B. Pingguan-Murphy, and N. A. Osman, "Developments of immobilized surface modified piezoelectric crystal biosensors for advanced applications," Int. J. Electrochem. Sci, vol. 8, pp. 8863-8892, 2013.
[34] K. Smyth and S.-G. Kim, "Experiment and simulation validated analytical equivalent circuit model for piezoelectric micromachined ultrasonic transducers," IEEE transactions on ultrasonics, ferroelectrics, and frequency control, vol. 62, no. 4, pp. 744-765, 2015.
[35] K. Smyth, S. Bathurst, F. Sammoura, and S.-G. Kim, "Analytic solution for N-electrode actuated piezoelectric disk with application to piezoelectric micromachined ultrasonic transducers," IEEE transactions on ultrasonics, ferroelectrics, and frequency control, vol. 60, no. 8, pp. 1756-1767, 2013.
[36] G. Shilpa, K. Sreelakshmi, and M. Ananthaprasad, "PZT thin film deposition techniques, properties and its application in ultrasonic MEMS sensors: A review," in IOP Conference Series: Materials Science and Engineering, 2016, vol. 149, no. 1: IOP Publishing, p. 012190.
[37] M. Hughes, "What Is RF Sputtering?," 2016.
[38] D. B. Chrisey and G. K. Hubler, "Pulsed laser deposition of thin films," 1994.
[39] C.-Q. Ye, "Sol-Gel Processes of Functional Powders and Films," Chem. React. Inorg. Chem, pp. 31-50, 2018.
[40] M. Birkholz, Thin film analysis by X-ray scattering. John Wiley & Sons, 2006.
[41] D. Hall, M. Cain, M. Stewart, T. C. f. M. M. National Physical Lab., and Technology, "Ferroelectric hysteresis measurement & analysis," in Minutes of the NPL CAM7 IAG Meeting, 1998.
[42] K. Akhtar, S. A. Khan, S. B. Khan, and A. M. Asiri, "Scanning electron microscopy: Principle and applications in nanomaterials characterization," in Handbook of materials characterization: Springer, 2018, pp. 113-145.
[43] A. Borowiak et al., "Pulsed laser deposition of epitaxial ferroelectric Pb (Zr, Ti) O3 films on silicon substrates," Thin Solid Films, vol. 520, no. 14, pp. 4604-4607, 2012.
[44] A. Chaipanich, "Effect of PZT particle size on dielectric and piezoelectric properties of PZT–cement composites," Current Applied Physics, vol. 7, no. 5, pp. 574-577, 2007.
[45] J. L. Cao et al., "Effects of thermal annealing on the structure of ferroelectric thin films," Journal of the American Ceramic Society, vol. 89, no. 4, pp. 1321-1325, 2006.
[46] A. Ababneh et al., "Electrical and morphological characterization of platinum thin-films with various adhesion layers for high temperature applications," Microsystem Technologies, vol. 23, no. 3, pp. 703-709, 2017.
[47] C. H. Huang et al., "Design, modelling, and characterization of display compatible pMUT device," 2018 19th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE), 2018, pp. 1-4.
[48] C. Chare et al., "Polymer-based piezoelectric ultrasound transducer arrays on glass demonstrating mid-air applications," 2020 IEEE International Ultrasonics Symposium (IUS), 2020, pp. 1-4.